Fuel smell in oil. cause?


#1

1990 Cherokee 4.oL str 6.

I was checking oil and noticed fuel smell in oil. lot of short trips but also driven til hot at least a couple of times every week with long rides weekly or bi weekly.

also smelling gas on start up and first minute or so

some fuel smell in exhaust.

the jeep runs well.

any idea of cause or risks?

thanks, wes


#2

Many cars smell of gas on startup, including my well maintained 2007 Totota. Nothing to worry about. Cars, especially older models run very rich mixtures on startup so you end up with a gas smell.

Smelling gas in the oil is another matter; you are not driving off the gas by letting ther car run hot enough for a sufficient lenghth of time. Cars only driven short distances will accumulate both water and raw gas in the oil, severely cutting engine life.

Take the car for a long (40 miles or so) drive at highway speed and then smell the oil. If it still smells of gas you have a ring problem with combution products finding their way into the crankcase.

Good luck!


#3

yeah i think i may have been smelling the start up fuel as i had moved the jeep right before checking oil. i just checked again and did not smell much fuel if any in oil.

thanks docnick.

i am taking a long ride tomorrow morning and will double check.

i think the fuel smell in exhaust is only after start up too


#4

Look for a leaking fuel pressure regulator or leaking fuel injector(s).

Tester


#5

checked those tester. no sign of leaks

the vacuum line and what i think is a fuel return from what i think is my charcoal canister are pretty old. maybe something is wrong there.

i guess its my canister, one of the ports says to carb bowl, tho i have no carb, goes to the air intake hose to the throttle body.

the other port starts off with rubber hose then connects to what looks like a metal fuel line. have not traced it from there tho.

misplaced my manual…


#6

lol. i guess i d better concentrate on getting these wheel well inserts done before it rains and i get water inside my body


#7

“driven til hot at least a couple of times every week” ; does this mean onto the red zone?

Clearly you have fuel getting into the oil and also unburned fuel getting pushed out with the exhaust. The odor is a dead giveaway. Unburned fuel getting into the exhaust is usually a sign of an injector problem or a cylinder not firing. Fuel getting into the oil, I’d suggest fuel getting pushed past bad rings or maybe a burned valve having allowed the valve stem seal to be destroyed and allowing the fuel to get pushed into the space under the valvecover during the compression cycle and washing down the oil returns with the oil. Since fuel is also going out the exhaust, I’ll betting on fried valves. Compression may be pushing fuel both into the exhaust system and up into the valvecover space via the same burned valve(s).

Try a compression test. See if you have a cylinder or two that won’t hold compression. I’m guessing bad valves.

Re: the overheating (if I interpreted you correctly), Focus on the compression test first. If I’m right, the heads have to come off and get worked on anyway.


#8

mountain I think doc nick has it right.

if you read my next post you ll see that I think I was mistaken about the fuel in the oil.
I had just started and moved the jeep and I think I was smelling the start up fuel by misytake and thinking it was on the dipstick. I had my head under the hood the whole time

the fuel in exhaust is just at start up too. its gone after I ride a bit.

no, I m never near the red zone as far as temp. by hot I meant up to operating temp. I m not a moron.

when I start it it is rich as my rpm s momentarily shoot up before immediately dropping to normal. that is when I have the fuel smells

I actually was reading my idle rpm wrong as insightful once suggested they are not as low as I thought, and that problem went away anyway after cleaning AIC valve

I think you are way off. the jeep runs great. no miss, great acceleration, no overheating.

I think my evap system may need some TLC and I definitely need to replace some old vacuum hoses.

thanks for your concern but the jeep is not nearly as bad as you seem to think.

I m trying to get it right is all. I need to break down and change the front seal tho. I am leaking more oil than I can live with.

I just changed the oil and tranny fluid and filter about a week ago and there was no fuel in it then.
I think I wasted my time on the tranny fluid as it seemed fine, but I did not know how long it had been.

thanks, wes


#9

Wes, I’m always happy to be wrong when it means that a vehicle is in much better shape than I envision.
Re: the comment on the heat, I did not mean to imply anything negative, I was just trying for clarification of the comment. Apologies if it came out wrong.


#10

no prob. sorry if I seemed testy :slight_smile:


#11

No problem at all.
Have a great evening.
TSM :slight_smile:


#12

The Cherokees with the 4.0L I6 and several other vehicles have often had fuel leaking from the injectors when cold started in cool weather (<32*F). Fuel would appear at the injector’s rubber seal at its base. There was never a pooling of fuel or even a drip but the odor of the fuel was apparent. Replacing all the injector seals always took care of the problem but so did warmer weather. Fuel in the oil would lead me to closely inspecting the fuel pressure regulator and checking for codes.


#13

i tried the key turning thing to get codes, but no luck. i think i was wrong about the fuel in the oil.

i didn t notice the gas smell this past winter, just the last couple of months. i think i may have some evaporative system problems.

i ll look at the injectors and regulator again.

what should i look for on the fuel press reg ?