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Diesel in Gas Engine

Last week I filled my tank and drove home approx 1 mile. The next morning I started having issues. Car wouldn’t start, had trouble at low idle and lots of smoke coming out of tail pipe. Once it warmed up it drove okay. Thought I had “bad” tank of gas so got dry gas and put it in. No change. Kept driving for 3 days - still with issues - and drove almost 150 miles in total. Coworkers said my car smelled of buring oil so had my husband checked oil. It had almost 7 qts too much - weird - but realized that the head gasket was probably blown. Towed it to repair shop and confirmed head gasket was shot. They made the repair and when I went to leave car had same issues - had to start, etc. So, checked and sensor readings were off. They replaced 02 sensor to see if that would help. But, they also realized that gas smelled funny. Upon further exploration discoved diesel was in my tank. Turns out local gas station’s fuel hauler had accidentally put diesel into unleaded tank. They have drained my car of all fuel, removed fuel filter, oil change, refilled with new fuel. My question is this…even though the car is driving fine, what is the chance of undetected damage to my car? The fuel hauler is accepting responsibility. I only bought the car 6 months ago (used) and has 88,385 miles on it. I want to make sure that the motor has not been compromised. Should I ask for preventative repairs? If so, what? I have a 2004 Subaru Outback wagon.

If they can get it back to where it passes compression and leakdown tests and accelerates, runs, and idles smoothy, doesn’t overheat, no check engine light, and passes an emission test with flying colors, that would be a good indication all the problems are fixed. You are right to be concerned. Everything in the fuel path, the pump, the fuel injectors, the fuel filter, the intake manifold seals, and the cat converter and possibly even the muffler are suspect at this point.

I doubt if you have any damage, diesel is a lubricant, but if it runs it likely will be running rough.  I suggest a fluid exchange

Have the fuel injectors cleaned.
Try to get somebody to reimburse you for those O2 sensors, because that wasn’t the problem.
Don’t accept the car as “fixed” until it passes smog.
And make sure you’re not the one paying for the smog.