The Diesel Dilemma

Print Friendly, PDF & Email

Diesel-powered cars could be the ticket – as far as giving us very high-mileage cars (50-plus MPGs) with excellent power/performance and without the liabilities of hybrids – including the additional expense/complexity of having two powerplants (a gas engine and an electric motor)  in the same vehicle – or the compromised economy/performance of hybrids at highway speeds.diesel lead

But, as my week in the just-launched 2014 Chevy Cruze diesel made all-too-plain, the government is making it very hard to make a case for diesel-powered cars.

I’ll explain.

The Cruze I test drove (read the review here) comes with two features that many potential buyers may not like. Unfortunately, they are not optional. If you buy the car, you’re stuck with them – just like Claymores in the dashboard (air bags), always-on headlights (Daytime Running Lamps) and other such things force-fed to the American car buyer.diesel particulate pic

The first of these features is a particulate (soot) trap built into the exhaust system. It must be periodically “regenerated.” Very high heat (from driving the car) is used to burn off accumulated soot, thereby preventing it from pouring out of the tailpipe. This is the chief reason why modern diesel cars don’t smoke – unlike the diesel-powered infamies of the past. This is wonderful. Except for one thing. If you don’t drive the car long enough or fast enough (20-30 minutes continuously at speeds of 30 MPH or more) the “regeneration” cycle won’t work as designed. The accumulated soot isn’t burned off. Instead, it builds up inside the system. Which makes the system unhappy. And that makes the car’s computer – which controls everything – unhappy. In turn, you will soon be unhappy. Because the car’s computer will flash a “trouble code” (a dashboard warning light will appear) and it will then limit how fast the car can be driven – until you take it in to Mr. Goodwrench to get that Great GM Feeling.particulate warning pic

If you do a lot of highway driving, you may never have this problem. But people who only use the car to commute, who do mostly stop-and-go driving, may be in for an unwelcome surprise. I wrote a column a few weeks ago (see here) about the DC ambulance that went kaput by the side of the road – with a dying patient inside – as a result of the vehicle’s computer getting pissy because the “regeneration” cycle never had a chance to do its thing – the ambulance being used infrequently and mostly driven for short distances at lower speeds. That was a Ford. Be advised the “regeneration” thing is by no means just a GM thing. It is becoming a universal thing – because it is the only thing that keeps particulate emissions in line with what the EPA demands. You can agree or not that curbing soot to nil is a good thing. The question is whether it’s smart to be so strict if the only way to do it is to make diesel-powered cars vulnerable to random unplanned pit stops. Because buyers aren’t going to like that. And once word gets out, they may not buy diesel-powered cars. Which kind of makes the whole exercise pointless. Unless the point of the exercise is to strangle diesel-powered cars in the crib, before they get a chance to win hearts and minds – and achieve widespread consumer acceptance.Cruze diesel fluid

The next diesel “feature” is potentially much more of a consumer turn-off: Urea injection.

You’ve no doubt heard about catalytic converters. All gas-powered cars have these devices. They catalytically (chemically) convert exhaust gasses from obnoxious and harmful to not-obnoxious and harmless – which is why the better part of any modern car’s exhaust stream (upwards of 95 percent) is composed of water vapor and carbon dioxide, both compounds having no ill effect on the quality of the air we breathe. Well, urea injection in diesel engines works on a similar principle. By spraying a shot of urea –  basically, horse pee – into the hot exhaust stream, the exhaust gas is chemically changed to more benign compounds. But unlike the gas-engined car’s catalytic converter – which requires no periodic maintenance – a diesel-powered car’s urea injection system requires regular topping-off of the urea tank. In the Cruze, there’s a filler neck in the trunk. The tank holds about five gallons of the stuff – which is typical.Cruze urea

So, what’s the problem?

First, there’s the additional cost of the urea – Chevy calls its version Diesel Exhaust Fluid; Mercedes-Benz calls it AdBlue – which ranges from around $7 a gallon at Wal-Mart to two or three times that at the dealership. The number of times you’ll have to top-off will vary depending on how many miles you drive – and how you drive (faster or slower) but the general rule is reportedly about once every 10,000 miles or so. Which means – if you drive the average 10,000 miles a year – you’ll be spending an additional $40-$50 annually (that’s the lowball, at Wal-Mart prices) for urea. Over say ten years, it’s a couple hundred bucks. No big deal, perhaps. But, annoying. And it also eats into the economic argument for buying a diesel, if the premise is buying it to save money.Cruze diesel gauge

However, the more serious issue with the urea injection is what happens if you allow the tank to run dry. In the case of the Cruze (and also Mercedes diesels and I’m pretty sure any diesel-powered new car with urea injection) the car’s computer will first limit the car’s maximum speed to 65 MPH. If ignored, the max drops to 55. Eventually, the car cannot be driven faster than 4 MPH – parking lot velocity – until it is taken (towed, probably) to the dealership for what will no doubt prove to be expensive service. The computer may also do this drill if it decides it doesn’t like the low-cost urea you bought at Wal-Mart. In which case, you will have no real choice but to buy the “official” product at the dealer – where it often costs $20 or more per gallon.Cruze close-up

Both these “features” add to the cost (and hassle) of owning a diesel car, as opposed to an otherwise-comparable gas-engined car. As a general rule, car buyers don’t like hassles – and car buyers interested in more economical cars (i.e., diesels) generally don’t like extra costs.

Adding salt to the wound is the unfortunate fact that diesel fuel now costs more than regular unleaded gasoline. Typically, 20-40 cents more per gallon, which is no small difference. diesel 2At .20 cents more per gallon per fill-up (assuming a 15 gallon tank) that’s an extra $3 per fill-up. If you fill up four times a month, that’s $12 extra per month – an additional $144 annually. Over ten years, that’s an additional $1,440 – not chump change.

This might not be a problem if the diesel-powered car made up for it by delivering stupendously superior fuel economy. But, alas, modern passenger car diesels – rendered less efficient by things like low sulfur diesel fuel, particulate traps and urea injection – are not all that much more economical than a growing number of gas engines, some of them available in the same car. The Chevy Cruze, for example, can be ordered with a 1.4 liter “Eco” gas engine that rates 28 MPG in city driving and 42 on the highway – vs. the optional diesel engine, which rates 33 city and 46 highway. The diesel’s mileage is better, but not stupendously so. Especially when you factor in the diesel’s  much higher buy-in cost ($24,855 vs. $19,835). The cost disparity is similar when you shop other cars, for example, the gas-burning version of the VW Jetta  ($15,545 for the base model with 2.0 gas engine and 24 city/34 highway) vs. $22,990 for the TDI diesel version ( 30 city, 42 highway).   diesel Jetta

Spending an extra $5k-plus to get an extra 6 or so MPG is not what I’d call a strong selling point.

Now, modern turbo-diesels do have the advantage of being potent performers, with push-you-back-in-your seat torque that really gets the car moving. But if the car stops moving because the particulate filter’s clogged – or the urea tank ran dry – none of that is going to matter.

Throw it in the Woods?  


  1. I have a 2006 Jetta TDI purchased new. I’m now pushing 208,000 miles on it. While advocates of diesel equipped vehicles like to claim a diesel “will run forever” they fail to address the other parts that comprise a diesel automobile/truck.

    In the last 10,000 miles I’ve had to replace calipers, coil springs, struts, shocks, wheel bearings, seat belts, lube and adjust the 5-speed, brake rotors front and rear, brake pads and other parts too minor to mention. Yes, much of what I mention is normal maintenance. But just remember as one proclaims how wonderful a diesel is, never forget the other parts/systems of the car are no different than a gasser. When they start shitting the bed, en masse, it may be time to think “new” or “new-used” car. Maybe.

  2. I live in Minnesota where temperatures often dip well below zero .. What happens to the urea solution and the sensors at -28 F ?

  3. I drive a 2006 MB E Class CDI. I now have 223,000 miles on it, almost all highway. I still get 37-38 mpg on the highway. The car has been regularly serviced at an MB dealership. The urea came in with the 2007 model year as “BlueTec”. California laws had a lot to do with it. The dealer charges $120 (+/-) for the urea refill, which is every 10,000 or 13,000 miles, I am not sure which is correct. Diesel is not a good option for stop and go urban-cycle driving, but it is great for highway driving, assuming your engine is turbocharged. In regard to the low-sulfur diesel, I put 4-6 ounces of Marvel Mystery Oil in every time I fill up. Transmission fluid will also work.

  4. I agree as far as the article goes, but I’ll add this: If you do nothing but short trips with your car (so regen cycles don’t happen or don’t complete), then you picked the wrong technology for your transportation. You shouldn’t be in a diesel car.

    And, however annoying the urea-injection technology, it sure is better than what it replaced, EGR that would plug up your intake manifold and make your car drive like a dog. If your car is artificially limiting your top speed because you don’t fill the urea tank, well the remedy is obvious – fill the tank!

    My 2013 Passat TDI is a MUCH better car than my 1997 Passat TDI although I really liked the latter too. Yeah, it’s annoying that government mandates ULSD, but it’s a bit like seatbelts. I wear seatbelts because I see the utility of wearing them – and in spite of the fact government mandates wearing them, which tends to reduce my incentive to wear them. But I still wear them.

  5. There has long been an easy way to make diesel exhaust clean – easy for a stationary engine, that is. You just run the exhaust through a sort of septic tank filled with earth that you change every so often. But for some reason people might be reluctant to lug one of those around in or behind a car…

  6. I had a German made 5 speed ’79 Rabbit diesel that gave 50 MPG and had adequate power in hilly Western Pennsylvania. The ex got it through a divorce, so I never knew how long it ran, but it was a wonderful little car, especially since it replaced my ’66 Riviera with a 425 that screamed going 55 MPH. I couldn’t give it more than 1/3 throttle from a stop without laying tire.

    I have a friend who was in Germany about 5 years ago and rented a VW Golf that gave 65 MPG (not KPG), he said. He was highly irritated that they were prohibited by Big Brother from being imported.

  7. Things like this remind my of my 87 corvette and the day I pulled out the old anemic 350 out and dropped a 383 in.

    The car had 3 catalytic converters. A primary and 2 smaller passive secondaries. The primary was hollowed out long ago. The two secondaries I was not aware of however. That is, until my headers got red hot about a minute after starting the new engine and with a loud bang, the platinum honeycomb material got crapped out of the exhaust.

    Cleaned the rest out with a screw driver. I like to think she was actively rejecting environmentalism.

  8. My 1983 Jetta turbo diesel got 60 mpg on the highway. A few years ago I looked at the new equivalent on a VW lot. It was heavier, larger displacement, cost twice as much, and the highway rating was in the 40s. Pathetic. I grew up driving turbocharged diesels, including a couple of stints running Cat-powered tractor-trailers all over the country. I’ve always preferred diesels because as long as you gave them fuel and air, they would never miss a beat. But now it looks like my ’95 Dodge Cummins pickup might be the last diesel I own, except for farm and lawn equipment. Oh well, at least they’ve finally figured out how to make a gas-burner run for more than 10 seconds without surging and stalling.

    • Ditto, Roland –

      Anyone old enough to remember the ’80s remembers 50-plus MPG diesel-powered cars that did not have the advantages (in particular, overdrive transmissions) that are universal today.

      It’s outrageous that the best these modern diesels can manage is no better than (and often worse than) diesel-powered cars routinely delivered 25-plus years ago.

      Now, of course, it’s also true that the older diesels were slow – by modern standards – but if the object of the exercise is economy… .

      A car that needs say 12-15 seconds to get to 60 is absolutely viable for everyday A to B driving. And if the reward was 60 MPG, I’m betting a lot of people would be fine with that level of performance.

      • Yes Eric, I’m sad to say that A to B is all I want from a car these days. I used to be a car nut but now for me it is just an appliance. With all the idiotic rules that only give drivers more reasons to become indignant, the less time I spend on the government roads the better. My first VW was a ’78 diesel Rabbit. I added a turbocharger, but the performance still was underwhelming. The Jetta was much better; nice looking and a fun little car to drive. What was it, something like 67 horsepower? But I would gladly pay $20k for one today.

        • Crikey!

          I applaud – from afar – his determination to do this swap; it’ll be interesting to see how it all pans out.
          One thing left out of the story, though, is what the retail cost of that Ecoboost engine and peripherals is. I’d guess at least $5k for the engine itself, plus probably another $2k for peripherals (not counting the transmission). Might be a lot more than that – assuming new parts, of course.

          I may be wrong about the cost – maybe it’s less – but either way, I’d like to know because it’s very relevant insofar as whether this project is realistic only if you’re rich or in a position to get free stuff from a major car company.

            • Yikes!

              That’s about what I figured…

              I wonder how much the engine controller (computer) adds?

              When all is said and done, I’m guessing it’d cost the average guy around $9,000 to buy/install this engine in his vehicle – not counting the transmission.

              Meanwhile, look at this:


              Long block 302 V-8, 340 hp. $3,769. Still needs a manifold, carb and ignition – also alternator, starter, water pump and so on. Figure another $2k or so for all that stuff.

              Let’s call it $6k.

              You’d get almost 100 more hp – and probably twice the torque – for $2-3K less. And if you wanted more power, my guess is that a simple $200 cam swap would get 400-plus hp out of this engine.

              Drop-in install. Numerous transmission choices, both automatic and manual – also direct-fit. No filthy computer needed. Basic electronics.

              That’s what I’d do if it were my car – and me paying the bills for the parts!

          • I thought the exercise was light weight and fuel economy with modern power and convenience?

            ‘put a 302 in it’ is so over done anyway.

            • I dunno… certainly, with a properly tuned FI system and ignition, that 302 would provide as much convenience (i.e,, driveability) and certainly more power for a lot less money.

              Over done?

              I guess that depends on your point of view.

              I see no good reason to spend significantly more money to get less performance (with more hassles, both in terms of the install and also in terms of maintaining the thing).

              Sure, he’ll have something different. I guess that’s worth something.

              Just not to me!

    • Haha, I know that feel. I like to mock people driving newer “economy” cars when I drive my nash metropolitan. It gets 35mpg, has a compression ratio of something like 7:1, has some style (at least compared to modern econoboxes), and is over 50 years old. And to me, that means they are getting screwed.

      • Hey Phil –

        One of the little projects I’d love to undertake would be to find an old VW Beetle and upgrade it with a stand-alone TBI system and a five speed (overdrive) transaxle in place of the stock 4-speed non-overdrive transaxle. These two upgrades would make the old Beetle “modern” in terms of driveability – easy starts in all weather, etc. – as well as probably capable of 50 MPG or more.

        And it could probably be done for less than $8,000 – including the car itself.

        • an amusing transplant I did some years back.. used to run a shop that did far too many VW cars…. took back a core 40 Hp upright (Typ 1) engine needing heads done… an easy and cheap fix for me at the time. Left it sitting in the rehab row for a while. Opportunity came to purchase a European Typ 3 chassis, a Ghia body 2 door, pancake 1500 engine, VERY dead. It sat for a while. Needed something cheap to drive… had the heads off the old 40 Hp Typ 1, redid to basic specs, reassembled, then dropped that into the Typ 3 Euro Ghia body. Not exactly a stoplight racer, but it would cruise at 70 MPH all day long and deliver 42 mpg. The tall final drive gears on the Ghia made the difference. Sort of like a long legged overdrive. Not fast out of the hole by any means, but the whole thing functioned quite well. Tossed in a spare 12 gallon fuel tank, giving a range of about 800 miles…. handy during the phoney fuel crunches of the 1970’s. The ultimate cheap to run car, though, was an ancient (1959, I think it was ) Mercedes Type 104 190 D four door. Ran well, delivered 45 mpg at highway speeds, comfortable, rock solid, handled amazingly well. Put a 35 gallon tank from a scrapped schoolbus into the boot, wired a Lucal electric fuel pump to transfer from the bus tank into the car’s main tank, made it from Vancouver BC to Los Angles and back during the Second Phoney Fuel Crunch… for safety, I did buy ten bucks of diesel at a truck stop in southern Oregon on the return, but don’t think I NEEDED that to get home to BC. We had all the fuel we wanted north of 49th, though.

        • Eric,

          Installing EFI on a air cooled VW engine would be cool. It has been done on a Corvair. In fact, someone is selling a kit for that. It costs about 1300 bucks for the kit. Add maybe another 700 for the extras. So it can be done for 2000 dollars. They use trottle body injection parts from a Chevy setup. They report a somewhat more powerful car.

          The main benefit is that the Corvair runs much more smoothly. It is easier to start. In other words, it is about drivability. I have to admit, I much prefer EFI to carburation.

  9. Eric,

    Inquiring minds might like to know…… if urea is horse piss, and they charge for it…..,..

    Could a frugal person collect the fluid by products of a six pack of beer use it for the urea tank? Would it need processing, like boiling it to concentrate it?

    I could see an opportunity someday. Say someone is stranded due to the empty urea tank….. some guy could be an unlikely hero by taking a strategic piss……..

  10. Interestingly enough, in 2005, Toyota and Ford were primed to go gung-ho with new diesel engine development. The powertrain engineers were excited about the new micro-burst injectors that pulsed 4 or 5 bursts of fuel instead of one blast. Smooth flame-front meant the diesel detonation rattle was diminished and the acceleration matched a good gasoline engine.

    I’ve always suspected that someone at government motors (either one of the bail-out queens) twisted some arms to get some time to “catch-up”.

    Naturally the eco-goons at the EPA were more than happy to write regulations to virtually eliminate passenger car diesels.

    The higher diesel price also reflects the massive military demand for fuel. They have money to burn (tax dollars are free), and more is printed every year.

    I’ve seen old diesels run on a variety of odd substances, including raw (unrefined) filtered crude oil. The light crude oil had a bit more butane in it than I thought wise, but ran a bulldozer just fine.

    • On that last point, I was wondering what would happen if you ran one of these modern diesel cars on petrol or paraffin (gasoline or kerosene, to you), if those are cheaper than “proper” diesel fuel? That is, not only how well/efficiently/cost effectively/responsively to the accelerator etc. would it run, but what wear and tear or safety issues or whatever would come up over time from it hitting the modern fuel systems and so on?

      • Hi PM,

        I can’t say as regards mechanical issues, but I know for certain that using other-than-ULSD in one of these vehicles will cause problems with the emissions systems and, in these vehicles, that entails more than just running around with the “check engine” light on. If you continue to drive with the “check engine” light on (a fault registered with the emissions system) after a certain mileage interval, the car’s computer will put the engine into “limp home” (reduced speed) mode until the vehicle is serviced and the system re-set.

        Of course, you’ll also have voided your factory warranty – and any repairs will be on you.

        • I suppose that goes for biodiesel, too… I wonder just what those systems are measuring? After all, petrol and paraffin are plain vanilla hydrocarbons like diesel fuel, just different molecular sizes.

      • Main issue with running the “lighter” fuels, as petrol and paraffin, is that they are solvents, not oils. Diesel fuel, along with “stove oil”, kerosene, jet fuel, are all light oils, the lubrication properties are essential for the survival of the fuel systems with their amazingly tight tolerances. The risk of galling, premature wear, etc, on the fuel metering systems is too high with the solvent fuels you mention. However, since most of the modern engines work at much higher fuel pressures, the use of much heavier oils for fuel is possible. I’ve been blending up to about ten percent waste oil (well filtered) into the fuel tank and can’t ever tell the difference in operation. I also will blend in, when available, lots of vegetable oils (also filtered) and even automatic trans fluid (used, filtered). Rotten petrol, being quite heavy, is also fair game, perhaps up to about 20%, but I’ll often toss in a gallon of used drain oil along with a few gallons of ancient petrol (salvaged from old cars, sitting, and heading off to the knacker, so must drain the fluids anyway). The old mechanical injectio Mercedes cars will eat almost anything, I’m a bit more skittish over what I feed my Powerstroke. Prefiltering is a must, and I have installed Racor 500 series fuel filter with the 2 micron paper element…… the fuel always looks black from the high lamp-black content of the old diesel engine drain oil, but still burns clean. I figure each gallon of drain oil burned up in this manner not only saves me four plus dollars (fuel not purchased) but also saves me the trouble of transporting it for giveaway disposal. I still have one early (1977) Mercedes 300 D, which I plan on holding on to for the Ship Hit the Span scenario…. it will burn nearly anything I put to it. Super low miles on the engine assures a remaining service life of at least 200K………


    Particulate filters are everywhere, particularly the left-leaning two-legged variety. They can be obtained cheaply from EPA office desks and completely free of charge when found chained to a tree or obtained from a “caaaahbn” rally.

    They’re a fully sustainable resource and are grown in large farms such as WWF, Greenpeace and Friends of the Earth.

    Fitting is no problem. Just stuff the filter FIRMLY onto the exhaust pipe. Front or back doesn’t matter, but from the back is preferable.

    They should last quite a while in operation and global taxes in their maintenance will be greatly reduced, since once fitted, they require no electricity or oxygen.

  12. Am vacationing in Chicago this week. Thanks to the clovers here gas is actually more expensive than diesel. Like 20 cents more expensive for unleaded!

  13. Diesels are more costly at the beginning, and include numerous little inconveniences throughout their service lives. Their massive engines are heavier, and make a vehicle more ponderous, too.

    In return, one gets more torque, better mpg, and (allegedly) longer engine life.

    The high heat regeneration, and urea exhaust fluid really don’t change the basic equation much at all. Personally, I don’t care for diesels, and wouldn’t buy one even if they didn’t have the two problems you mention……except……..

    Diesel fuel can be stored for much, much longer before it becomes unusable. Perhaps that doesn’t seem like a big deal. In my view of the future, it seems like a Very Big Deal. That’s why my next vehicle probably will be be a diesel. And I won’t mind stocking up on some extra exhaust fluid. Betcha that stuff can be stored for a long time too. 🙂

      • I love my three wire (fuel shutoff, glow plugs, starter) diesel 🙂 In a pinch I can go without any of those wires, though it’s a bit hard on the injection pump on shutdown.

      • eric, it really depends on what you do with diesel. Cruising down the road at significant expense in buying the vehicle, nope. Pulling a trailer or just hauling heavy loads in a pickup, yep, worth it for those who’ll be doing this regularly. And then there is the increase in the cooling systems, a/c, hydraulic(power steering)system(and this can be used for many PTO type spin offs such as winches, producing 120 V AC power with inverters and various other power accessories. One reason why diesels are so popular in the SW is their ability to not be affected nearly as much by heat as gasoline engines. You really think I care how much fuel(not anything to sweat over)my diesel pickup uses while I’m doing business, shopping or just stopping for fuel and drinks? I have responsibilities to my dogs, maybe cats, and human cargo to keep them cool and go to great lengths to do so for livestock not to mention those whiny humans. Everything, and I mean everything is bigger, hence better, than gasoline trucks. I know a few early 90’s GM gasoline(350’s, not the latter 5.7L) pickups that have over 500,000 M and still doing fine. Bar that, I’ll take the diesel. I’m just talking experience. And to michael.white, thank god for mechanical injection pumps. Just let me stop on the side of a good hill and I can go no matter what, starter or no, electricity or no(Need something in the range of 12 V’s but not a hot battery in any way). Clutch it, let it roll and then Gas It, I mean Loud Pedal It.

  14. So I guess the only feature left to tie on to would be the extra 100,000 miles that the diesel will last vs. the gas engine.

    This also relates back to your earlier post recommending buying a used car rather than a new one. A 3 – 4 year old car with 60-odd thousand miles on it should cost a good 40% less than a new one and if it will last those additional miles then might be an unbeatable combination.

    Keep up the good work, buddy.

    • Hi Scott,

      It will be interesting to find out whether these “next generation” turbo-diesels will be as long lived as older (pre-particulate filter/pre-urea injection) diesels have proved to be.

  15. I mostly agree with you, Eric, on this point. But let me add a little info to provide perspective.

    Ultra Low Sulfur Diesel (ULSD) – Sulfur is a naturally occurring element in diesel fuel. Previous diesel was already “low sulfur” and now all of it in the first world is “ultra low sulfur.” This reduces the amount of ash produced by diesel combustion and seems to be the primary reason why all diesels today are putting out much less soot, even the old ones. Problem is, it costs a lot of money to remove sulfur from diesel so it adds a lot to the price per gallon (seems to be about $0.20-0.40/gal). Also, sulfur is a lubricant so the engine parts may wear faster and not be as efficient, though this is only speculation since the technology is relatively new. Also, ULSD is not as available in third world countries. It’s somewhat prevalent in Mexico, but you have to look for it. Other areas, such as Africa and South America, may not have much at all.

    Diesel Prticulate Filter (DPF) – As mentioned, this is a physical filter that captures the ash/soot, a.k.a. “particulates,” from the exhaust. This must periodically be “regenerated” which means basically burning off the ash from the filter by very high temps. To do so, the exhaust system must be up to a certain temperature and then a small amount of diesel fuel is injected directly into the exhaust system which then combusts and raises the temp high enough to regenerate the filter. Depending on how you drive, the required temps can be reached, according to what I’ve read, in as little as five minutes, and is unlikely to be a common problem. It’s obviously a potential issue, as evidenced by your example with the ambulance. However, there are warning systems built in that detect the need for a regen cycle and will warn the driver of the need. The more problematic issues are the complexities and inefficiencies introduced. This is a whole new system, much more complicated than a catalytic converter, that would be prone to sensor failures, plugging up, etc. and it seems that this would introduce exhaust restriction, harming efficiency, and the obvious issue of injecting diesel into the exhaust, which means it is wasted as far as providing power to move the car. Thus despite general increases in diesel mileage, the mpg would likely be higher if this DPF system was not present. Not to mention the fact that all of this adds to the cost of a diesel car and takes up space. So while the concern of the DPF getting plugged and having to be repaired by the dealer may be small, these other issues are going to affect all owners.

    Diesel Exhaust Fluid (DEF) – Urea is basically piss, horse piss or human piss makes no difference. DEF is mostly urea. This piss is stored in a separate tank in the vehicle and must be filled separately. It is injected into the exhaust and chemically neutralizes the nitrous oxides (NOx) in the exhaust. Most vehicles I’ve seen have a tank that will last, on average, 10,000 miles between fill ups. They also have a warning light to inform the driver of the low urea tank about 1,000 miles before you run out, at least on a German made diesel. How much urea is needed depends on the size of the engine, but on my larger VW Touareg, it’ll cost me about $35 to fill it up, and you can find the DEF at any parts store, WalMart, and most gas stations that sell diesel, especially truck stops. I expect that it will come down in price as manufacturing processes improve. To me, it is onerous, but not much more than having to refill windshield washer fluid, and no worse thsn changing the oil, which costs about the same. The biggest problem I see is, yet again, the added weight, expense, and complexity of this system. I’ve got a whole new set of sensors, any one of which can fail, and an additional tank taking up space (beneath my spare tire, in my case). It’s another expense paid for by the consumer without any measurable benefit to him.

    Of these technologies, only ULSD is truly mandated by the Uncle. What IS mandated is a particularly low output of particulates and of NOx. These technologies were the first solution developed to meet these standards. They first hit the market around 2007-08, and were advertised as “clean diesel technology,” which while true, is a marketing misdirection. They should have been “government diesel penalty technology” instead. I imagine someone will figure out a way to bypass these systems rather than fix them in the future, which will be highly illegal since you’re circumventing emissions equipment, and we all know emissions compliance is much more important for the government to enforce than things like obeying constitutional limits on government power (which, incidentally, doesn’t include environmental protection).

    Of note, the new Mazda Skyactiv-D Diesel engine apparently doesn’t need DPF and DEF. It works by being the world’s lowest compression diesel engine. There’s apparently a lot of other tech involved, and its about 5 years newer than the DPF/DEF approach, but it saves cost and weight. I don’t know if it is as reliable as normal, high pressure diesels, or if it is much more complicated. I also dont know how much efficiency is lost with low pressure diesels. However, it meets emissions restrictions without complicated exhaust treatment systems. I’m sure the government hates that. The new Mazda 6 has this option, and the impending Mazda 3 next year will have a smaller displacement one. I’m guessing the SUVs will get a version, too, pretty soon.

    Don’t let the diesel emissions crap turn you off of considering one, but if its a real worry, look at a pre-2007 diesel vehicle or keep an eye on the Mazda-like diesels that will be popping up soon.

    • My A3 TDI doesn’t require DEF either. The larger VW/Audi engines use it. And you are correct, many of the rules come from California, not the federal government. I really can’t figure out why manufacturers don’t just tell CA to pound sand, or just have a dealer-add on kit for cars sold in Los Angles. I have no intention of driving to California, yet becuase the potential is there I have to live by their rules.

      The real crime is all this exhaust treatment means diesel engines put out less particulate and soot than gasoline engines, and what little soot does come out the pipe is much finer than the old days. This means it’s much more likely to pass through your lung’s natural filters and settle in.

    • Of note, the new Mazda Skyactiv-D Diesel engine apparently doesn’t need DPF and DEF. It works by being the world’s lowest compression diesel engine. There’s apparently a lot of other tech involved, and its about 5 years newer than the DPF/DEF approach, but it saves cost and weight. I don’t know if it is as reliable as normal, high pressure diesels, or if it is much more complicated. I also dont know how much efficiency is lost with low pressure diesels.

      In general, that technology is even older, simpler and more reliable than that of the diesel engine. The problems were start up time, lower efficiency (roughly, proportional to the lower compression, but better than its alternatives in its early days), and difficulty operating at other than low r.p.m. (and therefore, low power for the engine size and weight). The last is easy to fix with a diesel style injection near top dead centre (practical with modern injector pumps), and at a guess you might fix the first with a spark assist.

    • Helen, I watched No Country For Old Men yesterday and the most reliable truck in it was a ’70 Chevy 3/4 T 4WD. I wanted it all over again.

  16. How long before we start seeing devices like the old O2 sensor simulator that are designed to fool the computer into thinking the urea injection system is functioning properly?

    • I sure wouldn’t incite anyone to break the law except as an experiment, but I’d skip the O2 sensor and go for the MAP or MAF open loop idea instead. I’ve never owned a diesel before but I can kind of interpolate on gasoline engineering a bit. The idea that the O2 sensor (closed loop) is only used once the catalytic converter (engine warm up temps) is up to high enough temperatures. In the beginning stages (cold enginer or open loop) the MAP (manifold absolute pressure) or MAF (manifold air flow) sensor in the the intake manifold is used to gauge how much fuel to add based on intake pressure. Obviously the idea is that closed loop gives much MPG on a gasoline engine when running with the O2 sensor because its monitoring the complete combustion in a integrated loop (zero positional error in mixturing).

      What I imagine is that since old Diesels didn’t have O2 sensors because there wasn’t a catalytic converter that means that the old Diesels probably were using an equivalent of MAP or MAF open loop table lookup always to determine how much fuel to add? If this is true then if you want to get a new Diesel to act like an old Diesel Engine you need to replace the feedback end and all the useless sensors of the urea and 02 sensor with a simple open loop MAP fuel ratio. Its pretty easy to reprogram a cars computer to do whatever you want actually, I could do it for $20.00 guaranteed.

      The neat thing with diesel is that it has no spark plugs so there is no need to advance and retard timing like a gasoline engine so the control of a open loop mode would be that much simpler. All you have to do is read the absolute pressure in the manifold. Calculate by table lookup how much proportional fuel to inject and PWM (pulse width modulate) the injector valve (timed pulse jet turned all on or all off intervals) to get the right fuel interval. It would be actually refreshingly easy and fun for a beginner HS project, for a engineer, or for a self motivated and self learned person to do.

      If you’re interested let me know and I can give you some hints the best way to do it. Heck you might even sell it but I don’t know the legality of it. I’m thinking it might be possible to sell it as a limp kit to diagnose the functionality of the engine without the main computer involved. Also, I do know that if you purposefully ran said car down the road you’d probably be felonous and I can’t incite you do that. But as an educational experience or for a diagnostic limp mode engine test it would probably be ok if you know what I mean. Beings some people would run it that way for extended theoretical testing in their garage they’d be crazy to keep all the other stuff in the loop and probably want would want a way to keep the emission parts clean and stored (sensors, urea, O2 sensor, and catalytic converter). A catalytic converter sitting in the garage in prisitne condition could really be helpful to another guy with say another engine who needed those pristine parts to pass emission years later. I mean like in factory condition. Like I said keep the whole thing as an experiment but don’t break the law as that is bad news and so at least keep your diesel burning simple and pure with whatever legal loopholes it can breath its intake manifold through when performing your theoretical garage tune up experiments.

      • Most likely the MAP and MAF sensors are still there BTW as I’d imagine that the diesel having an O2 sensor has the same problem as a gasoline engine that it starts in open loop when the catalytic converter is still cold. So one shouldn’t even have to add these sensors and the wires to the computer ports would still be there. One probably replace the whole car computer with a 8 bit microcontroller that had A/D (analog to digital converters). Diesel like i said should be the easiest of all engines to bypass the main computer code close loop mode as there is no complicated timing and ingition problems. Many people fret and worry about electronics but its still the easiest part of the engine actually. I’d rather work as a sparkie any day versus a wrenchie greasy who has to lift a motor. Please my intellensia brethren the electronics is beneath you on all this sill stuff and nothing to fear for someones of your intellects.

        Hot Rod

        • Sorry if my mispellings and missing verbs and other canonical use of words is derelict. Hopefully you can still get the message minus my free spirit in writing in near perfect prose to convey it.

      • Most gasoline cars have at least two O2 sensors. One before the CAT in the exhaust manifold and one AFTER the CAT. The one before the cat is used for closed loop feedback. Over time its feedback is also used to trim the fuel tables used for open loop modes. The purpose of the O2 sensor after the cat is purely to test the cat to make sure it is working properly and/or fink on – oops, I mean inform the owner if the cat is not working by turning on the check engine light and setting relevant codes.


Please enter your comment!
Please enter your name here