6.0L chev gas in oil?

[bullet man]

I have 99 silverado with a 6.0L engine I do oil scan tests almost every oil change. the last 2 have come back showing a 7% fuel dilution in the oil. have talked to several GM techs and they said to replace fuel pressure regulator,so I did but it didnt help any. Now they dont know what could be wrong. the truck runs good and never throws a service engine light. how am i getting fuel in the oil?

[NCroadracer]

your injectors are probably bleeding fuel into the cylinders as the truck cools off after running, which seeps past the rings and down into the crankcase.

Try a good fuel injector clean or isolate the ones sticking open and replace them.

[z07]

Do you make a lot of short trips? If so, then the fuel in oil is to be expected.

The FPR wouldn't cause fuel in the oil. Suppose for a moment that the FPR's spring were replaced with a solid block. The fuel pressure would only rise to the max output of the fuel pump, call it 50 PSI.

As stated above, one or more injectors may be leaking.

No more guessing or throwing parts at it though. Put a fuel pressure gauge, $20 at any parts store, on the shreder valve on the rail and see what pressure is while running at idle[1], at 3k RPM[2], at shut off[3], 30 mins after shut off[4], and 12 hours after shut off[5].

1. 35-40 psi
2. 40-45 psi
3. 35-40 psi
4. 30-35 psi
5. 25-30 psi

[junior3382]

Perhaps I am not fully understanding this, but even if the injectors bled a bit, if the fuel leaks past the rings, wouldn't that indicate bad rings? I would also do a compression check to make sure the rings are not begining to wear out. If the injectors are fine, then the mix is occuring during combustion, and while the motor is running. Thats how i would see it, am I wrong? if so, what detail here am I missing?

[z07]

Originally Posted by junior3382

Perhaps I am not fully understanding this, but even if the injectors bled a bit, if the fuel leaks past the rings, wouldn't that indicate bad rings? I would also do a compression check to make sure the rings are not begining to wear out. If the injectors are fine, then the mix is occuring during combustion, and while the motor is running. Thats how i would see it, am I wrong? if so, what detail here am I missing?

You're on the right track but just shy of "fully understanding" IMHO.

Rings don't make a perfect seal in the cylinders. At normal operating temp they come fairly close but the seal, even on a new engine, isn't going to stop the flow of liquid fuel from getting past rings and into the crank case.

The seal made by the rings against the cylinder walls is at its worst when the engine is cold. So if gas is leaking after shut down it will make its way into the oil.

[junior3382]

Okay, that actually makes sense. Thank you.

[bullet man]

yeah ive checked fuel pressure and compression. fuel pressure at idle is about 45psi and at 3k is about 50-55psi. I was told that pressure shouldnt drop more than 5psi over 20 minutes with the engine shut off and it doesnt. i dont make many short trips at all. I ve pulled all of the plugs and none of them are dirty or different. My gm shop wont really tell me anything cause they want to work on it . Do you think an injection shop can drip test injectors like these? I was hoping that maybe this was a common problem and somebody knew an easy remedy. Im a pretty good gearhead myself but normally deal with old carbureted mud trucks.

[NCroadracer]

No matter what, there will always be traces of fuel in the oil. Even if your vehicle is new. unless the oil level is up due to fuel or if it actually smells like gas... I wouldn't worry too much about it.

[stumpuller454]

thats why i don`t spend the little bit to get samples from my truck, looking and sniffing the dipstick tells me enouh!hehe. i work on industrial engines and it is a regular thing to get samples, they more than often result in worthless goose chases for things found in the oil, i fully understand the reasoning though, gets you prepared for things i guess, if your oil turns black quickly between oil changes, then there is too much fuel in oil, or if it smells like gas on dipstick!(: