4.0L Engine Oil Cap Falling Off? - JeepForum.com
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post #1 of 4 Old 02-26-2013, 09:11 AM Thread Starter
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1998 TJ Wrangler 
Join Date: Mar 2011
Location: Topeka
Posts: 34
4.0L Engine Oil Cap Falling Off?

I have a '98 Wrangler with the 4.0L engine. At 146k miles a piston skirt broke, so I tore it apart and rebuilt the engine from the ground up. Before, the oil fill cap used to get stuck and I would nearly destroy it trying to get it out of the valve cover. It's been 10k miles since the rebuild and 3 times now the oil cap has worked it's way up out of the valve cover, twice I found it sitting on the opening and yesterday I found it laying in the parking lot at work accompanied by a pretty good trail of oil. I am not sure what could be causing this to happen, it is as if the valve cover has become pressurized to such an extent that it's forcing the cap to work it's way out. I did put in a high volume oil pump which bumped the cold oil pressure from 40 to 60 lbs (hot pressure from 20 to 40 lbs) and I believe there is a lifter bleeding off over night as every morning there is a nice light rattle for 2-3 seconds when I start the engine.

Any idea what could be causing this? I like to think that perhaps after destroying the last oil cap I bought one that just doesn't fit quite right, but I want to make sure that there couldn't be something more sinister at play here!

DasFrettchen is offline  
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post #2 of 4 Old 02-27-2013, 08:57 PM
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1987 YJ Wrangler 
Join Date: Dec 2009
Location: Mooresville
Posts: 113
check your PVC valve, if there is too much crank case pressure it is possiable it could pop off. If your PVC valve rattles it is ok. Make sure the hoses are not cloged. The valve cover has to vent air in, air out.
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post #3 of 4 Old 02-28-2013, 06:49 AM
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2000 TJ Wrangler 
Join Date: Apr 2005
Location: Elkmont
Posts: 10,048
The TJ doesn't have a PVC valve so shaking it won't tell you anything.

I doubt your problem is pressure related. I'd be checking the cap and maybe the hole in the cover it threads into.

Keep in mind that free advice can frequently be worth less than you pay for it.
mdm is offline  
post #4 of 4 Old 02-28-2013, 08:36 AM
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1995 ZJ 
Join Date: Mar 2005
Posts: 957
Do you have a breather ? is it working ? is the dip stick also being pushed up ?

1995 Jeep gc ltd, 2005 Jeep gc ltd , 71 Dart, 73 RR 440-6pk, 78 Mag GT, 85 Power Ram W-350, 92 Daytona, 99 Dakota, 08 Ram 2500

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4.0 , 4.0l , cap , engine , oil

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