Oil Alert For Older Cars

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In order to comply with federal requirements that key emissions control components on new cars such as catalytic converters work (and can be warranted to work)  for at least 120,000 miles (previously, it was 100,000 miles) automakers have been pushing for reductions in an oil additive known as zinc dialkyl dithio phosphate (ZDDP), which contains phosphorous (as well as zinc and manganese).

The problem for late model cars is that the phosphorous in ZDDP has been linked with premature catalytic converter failure – or at least, premature loss of converter efficiency.

But the problem for older cars (generally, stuff built before the early-mid 1980s) with flat tappet (vs. roller-type) camshafts is that oils with low ZDDP levels may accelerate wear and even cause premature failure, of flat tappet camshafts. In a nutshell, the ZDDP additives cushion the high pressure point between the lifter crown and the camshaft lobe, acting as an anti-friction, anti-wear barrier. The stuff is especially critical in just-rebuilt engines, during the initial break-in period.

Levels of ZDDP in commonly available mainstream motor oils – including big-name brands and high dollar synthetics – have been dropping since the new emissions longevity requirements became effective with the 2004 model year, almost eight years ago now. Unfortunately, many owners of older cars with flat tappet camshafts are unaware of the changing formulations – and the threat low-ZDDP (and even possibly no ZDDP) oils may represent.

The situation is analogous to the early 1970s, when lead (a lubricant and octane enhancer) began to disappear from gasoline. Engines that had been designed to burn leaded fuel – especially high-performance engines run at high RPMs – suffered premature valve recession caused by the use of unleaded fuel.

So, what to do about the disappearance of  ZDDP?

The first thing is to determine whether your vehicle is equipped with a flat tappet camshaft. If it’s an American-brand car or truck older than model year 1980 and the engine is a V-8 or V-6 (or inline six) the odds are virtually 100 percent certain that you have an engine with a flat tappet camshaft.

By the latter half of the ’80s and into the 1990s, roller-style camshafts were becoming the norm – and if you have a car from that era or newer, you are probably safe using currently available oil formulations.  But it’s important to be sure. You won’t find information on the type of camshaft your vehicle has in your owner’s manual. You’ll need to consult a technical service manual – or ask someone who is knowledgeable. The service manager at  a dealership for your make/model of car ought to know – or should be able to find out.

What to use?

There are still a few oils on the market that have adequate (pre-2004)  levels of ZDDP. These include Shell Rotella T – a conventional (mineral-based) oil that was originally formulated for diesel engines. Rotella T still contains 1,200 parts per million ZDDP, according to Shell – which is as much as five times the amount found in other oils. Don’t sweat it that Rotella was/is marketed “for diesels.” It’s also an excellent choice for older, non-emissions controlled engines with flat tappet cams that need their ZDDP. Rotella’s also modestly priced and readily available at most any auto parts store. Shell also markets a synthetic version of Rotella that offers even more protection – as well as longevity and a 5W-40 viscosity for those who operate their vehicles in colder climates. Standard Rotella comes in a heavier 15W-40 blend.

Another choice – in a full synthetic – is Amsoil which carries a line of oils with ZDDP in popular viscosities such as 10W-40 and heavier 20W-50.  Redline oil  is also still fine for older engines with flat tappet cams. Unfortunately, both Amsoil and Redline can be hard to find at your local store; but if you plan ahead, you can order a case from any one of multiple suppliers online and just keep a stash on hand. Royal Purple is good stuff, too – and(at least in my area, Virginia) is usually available at your local major auto parts place.

Another option is additives. GM used to sell an over the counter Engine Oil Supplement (EOS) that was just what the doctor ordered – and for only about $12 per bottle. Unfortunately, GM stopped making the stuff and it’s now very hard to find.

Competition Cams does offer something similar – its Engine Break-in Oil Additive. Comp cams used to recommend this for initial break-in but now recommends that it be added with the oil at every oil change. From Tech Bulletin 225:

“While this additive was originally developed specifically for break-in protection, subsequent testing has proven the durability benefits of its long term use. This special blend of additives promotes proper break-in and protects against premature cam and lifter failure by replacing some of the beneficial ingredients that the oil companies have been required to remove from off the shelf oil.”

So, FYI –


  1. Eric,

    I know this is an old article, but as airhead owner, this is near and dear to my heart.

    The correct oil can be tricky to determine in older machines and you have hit all of the right issues. One of the problems from what I can tell is that it is hard to determine the exact composition of some oils.

    I use Golden Spectro 4 20W-50W or the non-synthetic BMW 20W-50W oil in my 77 R100. I am always concerned that using full synthetic oil may cause issues with various seals.

    Snowbum has a good rundown on oils for old BMW motorcycles, which is also applicable to many older cars.


    If you have a couple of extra days, his technical articles on BMW motorcycles are worth a read.


    No affiliation, I just find them useful.


  2. Eric,

    First thanks for the mention on AMSOIL and I appreciate you being a fellow libertarian. AMSOIL now offers 3 high ZDDP oils, Z-ROD 10W30 and 20W50 motor oils as well as a straight SAE 30 Break-In oil.

    Also of note to re-builders, they offer and Engine Assembly Lube.

    If any of your readers is interested and wants to stock up, I’d suggest they sign up as preferred customers and buy at wholesale. Just visit my web site and give me a call. Be happy to help.


  3. I have used Shell Rotella T in my race and street cars with flat tappet engines since the mid-’60s and found it to be more than adequate. I never heard of ZDDP until a friend directed me to this site. Since Rotella T has/had what used to be a “DG” (diesel general)rating from SAE, I have had confidence in it in my Porsches, both pushrod and OHC, and several race engines including US V8s, and have never had an oil-caused problem. It’s cheap, it comes in 5 qt jugs, and can be found at any truck stop in the 15W-40 version. Nice to know I don’t need to do anything different than I have been doing all along, although for other reasons.

  4. Dear Eric Peters Autos,

    OK, please be gentle. I’m not a car person. But I have a clarification request: Based on the the article, this does not affect diesels, correct? Because I’m interested in a 1987 MB Sedan.


    Quantella Owens

    • Hi Quantella,

      Welcome, first of all!

      Your’ 87 MB may already have an overdrive transmission; MBs of that era were well ahead of other cars, technologically speaking. And being a diesel, it’s injected.

      So, the modifications mentioned in the article aren’t for you. But you could probably get a mileage improvement by switching over to synthetic lubricants – which will also certainly improve longevity and drivability.

    • QO,

      I love my ’87 300D sedan! 30+MPG, comfort for 5, and oil changes once a year. (I only put 5-6,000 miles per annum on the beast. It’s sitting on 138,000 miles now, and I expect it last me the rest of my life. (I’m 66…)

      You can’t go wrong with this beast.

      • Hi Bo,

        Those ’80s Benzes (diesels) were magnificently overbuilt. They will last literally decades with decent care. Hang on to that one!

  5. Royal Purple is your friend.

    Note that there are now three different “flavors” of RP:
    Regular–which in the newest grade will conform to the bullshit new regulation
    HPS–which has the “old”…that is, current…level of ZDP/ZDDP
    XPR–which is technically their “racing” oil, and has full-on levels of ZDP/ZDDP. I spoke to one of their techs–they’re right here near Houston in Conroe–and he reckons that if your engine isn’t burning oil like a fiend, you won’t destroy your cats with the XPR.

    I’m running the XPR in my e39 M5 and so far, so good; it seems like a fine replacement for the Castrol TWS BMW recommends.

    Dom you’ll love this: you can order 5 gallon containers of this lovely stuff from Amazon! I like having a big supply. Seems stupid to go hunting for it every time you do a change, and if you believe like I do there’s going to be massive inflation starting next year, might as well buy it while it’s cheap.

    I think I shared the story of my Blackstone Labs analysis already on this site so I won’t bore you guys. But suffice it to say that in back-to-back comparisons on my wife’s Infiniti, Royal Purple smoked Mobil One.

  6. I have several mid-90s Toyotas that have overhead camshafts that actuate flat tappets. If there are overhead cam systems that have roller tappets I’m not aware of them (which certainly has no bearing on whether they actually exist or not).

    This article on tappets in Wikipedia doesn’t even mention roller tappets http://en.wikipedia.org/wiki/Tappet

    If you know of an instance of OHC or DOHC setups with roller tappets I’d love to learn more about it.

    • I think they’re concerned mostly with pushrod engines with flat tappets, because the valve spring pressures are so much higher to deal with all the extra mass of pushrods and rockers.

      In a OHC/DOHC design the spring tensions are less…

      But I still like my ZDDP and I’ll be using my Royal Purple HPS or XPR. Screw the catalysts–they’re more easily replaced than my valvetrain!

  7. Rislone has been promoting their own ZDDP additive in the industry mags, tried to get it at NAPA, they don’t list it yet. Might be of some use whenever it gets available.

    • My buddy Graves – who owns/runs a repair shop – tells me it varies; that you really have to keep on top of the deals. Sometimes he buys drums, sometimes he buys cases. There is also the variable of brand/type. It’s kind of like buying gas, I think.

      I use Royal Purple in the TA and only high-end synthetics (Motul, etc.) in the bikes. I never cheap out on oil. But then again, I run my stuff hard – and want it to last long!

      PS: Power back on yet?

      • Yeah, power is back. My cable and telephone lines broke loose from the poles and are under some tree branches now. I need to cut them out and call the service guys to come put them back in the air. Also, I have a tension cable thing for the power line that snapped (it’s on my roof). My power line to my house is so low I can touch it! Yard is an ice field right now. Took the day off to get caught up.

        Ideally, I would like to have enough oil on hand for two years. I really like the five quart jugs and cases too. I’ve been using Walmart oil forever now, but always change before 3,000.

      • Hey I have a 03 toyota ecco that we have discovered the inside of the engine is covered in purple goo like substance. What do you think this is? The dealership wants me to replace my engine.

        • Purple goo, that is a new one to me. First thoughts are maybe milky oil, but that would be brownish chocolate shake. Wonder if you have some special color coolant? Could be power steering fluid. Wonder if an AC line busted and there was purple dye in it? Tough to say.. You need more information from the stealer.

          Oh wait! You said inside the engine. Sounds like a blown head gasket to me! If there is enough damage that can easily be an entire engine replacement.

        • Hi Karen,

          Purple goo is new to me, too. The only thing that comes to mind is the possibility that someone used Royal Purple oil – which is purple hued. If so, don’t get too worried as Royal Purple is premium oil. The goo, though, indicates sludge formation. How is the engine actually running? Is it running at all? Please give us more info and we’ll see what we can offer in the way of advice….

          Addendum: I had another thought; that goo could be engine assembly lube residue. Again, not necessarily a major problem. The Big Question here is: How is the engine running? Why does the shop want to do major work? What do they specifically claim is wrong with the engine?


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