Gas in the oil? What causes this? - JeepForum.com

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post #1 of 18 Old 04-20-2013, 05:08 PM Thread Starter
CJ7KAHUNA
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Gas in the oil? What causes this?

I previously posted that my nephew just got a 77 CJ5. While checking the oil today he smelled the heavy odor or gas on the dipstick. He decided to change the oil and found the oil to be very thin and it had a heavy gas smell to it. Once the new oil was in he noticed a dramatic increase in oil pressure (before he changed the oil he thought the oil pressure gauge was broke). He took it for a drive and checked it again and it the oil pressure is decreasing and the gas odor in the oil is coming back.

What would cause gas to get in the oil? The only thing I can think of is that he has a dead spark plug or 2 possibly causing gas to build up in the cylinder?????? I am no mechanic but I just cant think of any other place gas enters the engine.

Anybody ever dealt with this problem?

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post #2 of 18 Old 04-20-2013, 05:10 PM
Centerfire
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Its usually a fuel pump.
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post #3 of 18 Old 04-20-2013, 05:20 PM Thread Starter
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Quote:
Originally Posted by Centerfire View Post
Its usually a fuel pump.
Thanks for the input - is there anything else that can cause it?
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post #4 of 18 Old 04-20-2013, 05:29 PM
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I've seen gas get by the rings and end up in the oil as well.

X2 on the fuel pump. Most likely culprit.

Beat it to fit, paint it to match!

Wheel, Wrench, Repeat.
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post #5 of 18 Old 04-20-2013, 05:46 PM
John Strenk
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pumping the carb a lot trying to start it and not starting will dump a lot of gas into the cyliners and run past the ring
So will a carb that leaks into the intake after it's turned of but this dumps very little gas

A bad fuel pump is a place were gas is actually pumped into the crankcase.

Hope you do have good rings, because I've seen valve covers blown off the engine when so much gas was sitting in the pan the fumes pops in the crankcase....
usually nothing much damaged other than a valve cover destroyed....


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post #6 of 18 Old 04-20-2013, 06:33 PM Thread Starter
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Quote:
Originally Posted by John Strenk View Post
pumping the carb a lot trying to start it and not starting will dump a lot of gas into the cyliners and run past the ring
So will a carb that leaks into the intake after it's turned of but this dumps very little gas

A bad fuel pump is a place were gas is actually pumped into the crankcase.

Hope you do have good rings, because I've seen valve covers blown off the engine when so much gas was sitting in the pan the fumes pops in the crankcase....
usually nothing much damaged other than a valve cover destroyed....

He just got the jeep and it supposedly the motor is a fresh rebuild with about 5k on it. He is on his way out to get a fuel pump for it now. He is getting a set of plugs as well.
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post #7 of 18 Old 04-20-2013, 06:38 PM
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were the plugs wet with fuel???

I should also ask'

Carb or fuel injection?


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post #8 of 18 Old 04-20-2013, 06:40 PM
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you may want to check compression....
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post #9 of 18 Old 04-20-2013, 06:41 PM Thread Starter
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Quote:
Originally Posted by John Strenk View Post
were the plugs wet with fuel???
Said they were dark but not wet - sent me this pic, its a little out of focus (he's in NC I am in La)
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post #10 of 18 Old 04-20-2013, 06:46 PM
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That OK, we can work on dark later....
If they were wet, well that's a different problem...


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post #11 of 18 Old 04-20-2013, 06:48 PM Thread Starter
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Quote:
Originally Posted by John Strenk View Post
That OK, we can work on dark later....
If they were wet, well that's a different problem...
Cant really tell from the pic but he says they were not wet. Dark is running rich?
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post #12 of 18 Old 04-20-2013, 07:31 PM
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usually but there can be other factors..


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post #13 of 18 Old 04-21-2013, 03:53 PM Thread Starter
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Quote:
Originally Posted by John Strenk View Post
usually but there can be other factors..
What are some other factors besides a rich fuel mixture?
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post #14 of 18 Old 04-21-2013, 04:23 PM
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I wouldn't look too far into the plugs. They may be black but they aren't wet so i doubt the high volume of fuel is coming through the intake. With the amount of fuel he has in the oil I'd be telling your friend to try the fuel pump replacement and not drive it until he gets the issue fixed.

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post #15 of 18 Old 04-21-2013, 04:32 PM
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I had this problem on an FE series big block... Couldn't for the life of me figure why! I installed a new fuel pump, changed carbs... Turned out I had installed an aftermarket fuel tank and mounted it in the bed of the truck, instead of the pickup tube dropping into the tank (like it should) the tank I had was plumbed through the bottom, allowing any change in pressure (you have seen a gas can get hot and expand) push fuel right past the carb and down into the intake. I put a valve inline after the tank and pretty much solved the problem, you may however, have a clogged fuel vent and your system could be acting the same way.

Other than that, I would go with the diaphragm has blown out in your fuel pump!

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