Diesel in a gasoline engine - what do I do?

Dear Car Talk

Dear Car Talk | Jul 01, 2004

Dear Tom and Ray:

This evening, my overworked, overbooked, type-A wife accidentally put about 3.5 gallons of diesel into her nearly empty 1998 Honda Odyssey. Upon realizing her mistake, she filled up the rest of the 12-gallon tank with gasoline. At that point, she wisely decided to call me before trying to drive it. I told her to park it, and I immediately called two mechanics to get their advice.

I first called the dealer, and he said not to drive the car and to have it towed in. He said he would have to drain the gas tank and steam-clean it to get the diesel out and then check to see how far into the system the diesel fuel might have gotten. If we were lucky, it wouldn't have gotten sucked into the fuel pump, the fuel line or the injectors. If we weren't lucky, the dealer sure would be!

Then I called my trusty curbside mechanic, who comes to the house with all his tools and equipment in his truck and always provides me with reliable repair service for about a quarter of what the dealer quotes. He said that we probably could drive it. It would smoke some while the diesel burned out, but he thought that it might be OK, except maybe we would have to replace the oxygen sensors. I usually like to take the path of least resistance, but in this case I felt it would be better to be safe than sorry, and we had the car towed in for service. What should we do before driving it? Thank you, and don't fuel like my wife.

-- Neill

RAY: Well, I think the dealer gave you the correct advice, Neil. But you might not need to be quite as thorough as he's suggesting. And you certainly don't have to let him do the work, if you like your buddy, Crusty McToolbox, better.

TOM: It sounds like your wife never even ran the engine with the diesel fuel. So, we can say with confidence that none of it got into the fuel lines. All of it's still in the tank.

RAY: The tank needs to be removed and drained. You can probably skip the steam-cleaning phase, as I'm guessing that less than half a cup of diesel will remain on the fuel-tank walls.

TOM: After you reinstall the tank and refill it with gasoline, I'd have Crusty remove the fuel line where it joins the fuel rail, up in the engine compartment. Then you can cycle the fuel pump (without running the engine) and take a sample of the fuel in a glass bottle. Let it settle out and see if it looks clean. Do this several times, or until you get good, clean-looking gasoline. Then hook everything back up and drive it.

RAY: The fuel injectors shouldn't be bothered, even if there is still a tiny amount of diluted diesel fuel in the tank -- it'll just burn right up in the cylinders without any problem. Crusty is right, though, that if you ran a quantity of diesel through the engine, you'd be putting the oxygen sensors at real risk. And they're not cheap to replace.

TOM: But I don't think the diluted remnants of half a cup of diesel fuel in 12 gallons of gasoline will do any harm. Of course, if we're wrong and your fuel system is ruined, let us know, so we can warn the next poor schlub who does this. Good luck, Neil.

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