Reader Q (August 25, 2017)

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Here is the latest reader Q, along with my reply!

Michael asks:

First I love your articles. I’ve learned a lot. Now my question. What is your take on propane injection systems for diesels? I know that Australia has been promoting their use for a couple of decades and from what I can gather they are gaining popularity here in the US. I knew a guy who installed such a system on his F250. He increased mileage to 21 mpg and supposedly increased hp by upwards of 100 hp.

I realize they are not for everyone and may be more in the purview of the do it yourselfer, but I would still like your opinion.

Hi Michael: 

I haven’t got any personal/direct experience with the use of propane or CNG in a compression-ignition engine, but my main concern would be the use of a fuel (any fuel) in an engine that wasn’t designed for that fuel.

Propane/CNG have different properties (lubricity, volatility; combust differently) than diesel fuel.

Whether the differences are functionally meaningful would be the thing.

You would also, of course, have to modify the fuel system for pressurized gas rather than liquid and that could get pricey.

Emissions might be lower – or different – or worse. But the real problem is that – in the U.S. – it is illegal to modify or tamper with emissions-related components (this includes the fuel system) regardless of the actual effect on tailpipe exhaust emissions.

In other words, such a mod would likely result in the vehicle failing smog check – even if it doesn’t actually emit smog – which renders the vehicle effectively useless since you need to pass smog check in most states to get or renew vehicle registration.

And of course, your warranty would be void.

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  1. It’s been 7 to 8 years ago the propane injection craze happened here. This is diesel country and everyone was looking for that mythical fuel mileage of teens with that one ton pickup and that 3 or 4 axle 5th wheel RV trailer or the way overweight gooseneck.

    One guy locally was installing these systems all day every day for a while there.

    There were automatic and manual both that supposedly did the same thing…..something I never got a definitive answer about.

    Nobody had the skinny on long term effects on the engine but I think the reason it was a flash in the pan were the catastrophic effects some had in the long run.

    Don’t get me wrong, I’d like to have had extra power and especially fuel mileage but being a trucker my whole life every time I thought about it I had more questions than answers, except for a few trade-ins involving a car hauler and a bath at the dealer since a dead diesel pickup isn’t worth squat.

    Most just kept the dead one and looked for a used replacement engine.

    We were already dealing with fuel with warnings on the pump concerning the lack of sulphur and the effects it could have on your not brand new engine made for the old fuel.

    I figured if it were a viable long term thing then Detroit Diesel, Cummins, Cat, Mack and the like would be using it, no add on anything.

    I watched a youtube video yesterday of the Detroit Diesel manufacturing facility with them making the new engine that replaces the venerable 60 Series. It was pure pleasure, but no mention was made about the injection of anything but diesel.


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