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Q: Bad mileage & strong gas smell in dipstick/oil pan - 1996 Nissan 300ZX

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I started checking out my car because I was getting very bad mileage. When checking the oil dipstick, there was a strong smell, distinctive of gasoline. I removed the oil pan and the smell was even worse. I’ve been told many, many things by other people, but I don’t want to guess and replace things until I’m able to figure out what is wrong with it and fix it the first time. My mechanic tells me that he can’t and won’t diagnose it manually. I’ve been told different things: it’s the fuel dampener, the fuel regulator, piston rings, fuel injectors, engine valves not seated right, malfunctioning engine temperature regulator/thermostat, leak in the fuel line… In your professional opinion, what is the problem?

A: Okay, so usually the answer to problems are...

Okay, so usually the answer to problems are usually hidden in the fine details. The whole reason you started noticing a problem was the gas mileage. If this was my car, I would be thinking that I have a fuel injector stuck open or for some other reason, the engine is letting more fuel be used than is neccessary. Piston rings are not air or liquid tight. If you have an incredibly rich mixture (more fuel than you can burn) it will make the oil smell like gas, but that doesn’t mean anything is wrong with the rings necessarily. A leak in the fuel line would explain the mileage but not the oil smelling like gas. The only thing that explains both symptoms is that the extra fuel is entering the combustion chamber. I am betting it is something related to the system regulating fuel into the combustion chamber. I wish I could stick my finger on just one thing, but I hope I helped narrow it down a bit. Yet, if you would like, a certified technician from YourMechanic can come to your home or office, and definitively diagnose your poor gas mileage issue.

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