August 17, 2014

Car Talk

Diesel fuel in a gasoline car can be a real nightmare

Syndicated columnists

Dear Tom and Ray:

I woke up screaming the other night, as I'd dreamed I had just pumped five gallons of diesel fuel into my Prius. Back in the '50s, I heard on the radio (maybe it was your grandfather's show, "Buggy Talk"?) that adding a gallon of diesel fuel to a full tank of gas would add "top-cylinder lubrication." I tried it several times on my '53 Plymouth on trips, with no ill effect. What would happen if I did that today? — David

Tom: Your wallet would be $1,000 lighter.

Ray: It most likely would ruin your catalytic converter.

That's why you got away with it in your '53 Plymouth, which had absolutely no emissions equipment.

Ray: Diesel fuel is cleaner than it used to be; you no longer see sticks and rocks and dinosaur bones in it. So it mixes easily with the gasoline, and probably would pass through the fuel pump and fuel injectors without doing harm.

But it probably would kill your catalyst, and you'd never pass an emissions inspection without that.

When a customer of ours accidentally puts diesel fuel in a gasoline car, we have him or her tow it in. We remove the gas tank and drain it completely. Then we refill the tank with gasoline, and run the fuel pump with all of the fuel injectors removed — we just let the fuel injectors spray into a container.

Tom: So that second tank of gasoline flushes out the fuel line and the injectors without running the gasoline through the engine.

There's obviously a small amount of diesel fuel that was left on the walls of the tank. But that gets dissolved in that second tank of gasoline and diluted to the point where it's harmless.

Hope that helps, David. Now, pour yourself a cup of warm milk and go back to sleep.

(Car Talk is a nationally syndicated column by automotive experts (and brothers) Tom and Ray Magliozzi. Write to them at the Car Talk website.)


Partner video