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Old 08-12-2008, 07:22 PM
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Question Why is oil blowing out my dipstick tube?

I have built a few dozen engines of various types over the years and have done all my maintenance all my life but I seem to have a problem I can't figure out!

1977 CJ5 4.2L engine. All seemed fine until I replaced my PCV valve during a regular oil, oil and air filter change. No reason, I just figured it couldn't hurt. Well a short time later, I noticed a lot of oil drips in my garage. I figured the PCV was wrong and went back to the store with it and sure enough it was. I got the "right" one this time but I still have a problem.

Now here is where it gets a little funny. Not ha, ha funny either. I cleaned the engine block with brake cleaner so it was clean and dry. I cranked the engine, manually set the auto choke high idle cam on the highest idle speed and left it running for 1 1/2 hours. I came back and not a drop of oil on the engine or the floor. By the way, all the oil wetness is around the dipstick tube. So, I drove it .8 miles to my buddy's gas station and back and the engine was soaked in oil from the dip stick tube back. I cleaned it off again and this time I removed the dipstick from the tube, fitted a rubber hose about 2 ft long over the dipstick tube and ran it up to a little empty plastic can and did the 1.6 mile round trip again. There was several ounces of oil in the can that came out the dipstick tube, through the hose into the can!

I revved the engine several times and could not get a drop to come out. It only blows out the dipstick tube when the Jeep is actually moving down the road. This is freaking me out! I can do nothing to cause oil to blow out the tube sitting still. By the way, I didn't exceed 25 mph to the store and back and drove at normal engine speeds.

My first thought was a broken compression ring creating pressure in the crankcase. But if this was true, the pressure would be created whether or not the Jeep was moving or not. Right?

Today I replaced the PCV valve again. I put a new oil fill cap on. I checked the PCV valve for a "rattle". It rattles. I cranked the engine to see if vacuum was present at the PCV valve and it is. I have good vacuum. I have good oil pressure, about 40+ at speed.

Any one got any ideas??
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Old 08-12-2008, 07:28 PM
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Quote:
all the oil wetness is around the dipstick tube
Where on the dipstick? They do crack just above the block, often so you can't see the crack. Then oil is pushed out the crack.
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Old 08-12-2008, 07:46 PM
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Sitting still on the fast idle cam there will be very high manifold vacuum. Driving down the road at the same engine speed the vacuum will be lower, and pulling away from a stop it will be even lower. That might have something to do with it, but the exact mechanism escapes me.

As another experiment you might try making the trip with the PCV valve out of the valve cover - just an open hole.
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Old 08-12-2008, 08:59 PM
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Quote:
Originally Posted by LEVE View Post
Where on the dipstick? They do crack just above the block, often so you can't see the crack. Then oil is pushed out the crack.
It is coming out the tube. I put a hose on it and ran it to a canister and it deposited oil into the canister.
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Old 08-12-2008, 09:00 PM
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Quote:
Originally Posted by Jim_Lou View Post
Sitting still on the fast idle cam there will be very high manifold vacuum. Driving down the road at the same engine speed the vacuum will be lower, and pulling away from a stop it will be even lower. That might have something to do with it, but the exact mechanism escapes me.

As another experiment you might try making the trip with the PCV valve out of the valve cover - just an open hole.
Good idea. I will try that and post results.

By the way, the carrier worked great. Got the Lock Right installed with the one piece axles and all is good with the rear end!
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Old 08-12-2008, 11:43 PM
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I had the same problem on my first jeep. At the end of the day the rings were shot. I'm guessing the best thing for you to do right now is head to autodrone and borrow a compression tester and have at it.
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Old 08-13-2008, 12:09 AM
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Have you checked the PCV valve to make sure it's working? Even though it may be new, it can still fail. Also, IIRC, there's a baffle inside the valve cover. If it's plugged/pugging, the crankcase pressure will increase.
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Old 08-13-2008, 06:21 AM
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Glad the carrier worked. I hope this problem is as simple.
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Old 08-13-2008, 10:27 AM
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Quote:
Originally Posted by wrgarrett View Post
All seemed fine until I replaced my PCV valve during a regular oil, oil and air filter change. No reason, I just figured it couldn't hurt.
Did though didnít it?

Try replacing the hose to the PCV valve. My guess is either it cracked when you moved it or the new PCV valve isnít sealing because the old hose is hard.
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Old 08-13-2008, 05:54 PM
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How about the rubber grommet in the valve cover? It could have gotten britle from age
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