4.0L Engine Oil Cap Falling Off? - JeepForum.com
Sign Up   Today's Posts
User: Pass: Remember?
Advertise Here
Jeep Home Jeep Forum Jeep Classifieds Jeep Registry JeepSpace Jeep Reviews Jeep Gallery Jeep Clubs Jeep Groups Jeep Videos Jeep Events Jeep Articles
Go Back JeepForum.com > General Technical Discussions > Engines & Drivetrain > 4.0L Engine Oil Cap Falling Off?

Introducing MONSTALINER™ UV Permanent DIY Roll On Bed LineWeekend sale!! Our dual battery tray on sale $199FS: 2007-2013 Jeep Wrangler "HALO" Angel Eye Kit

Unread 02-26-2013, 08:11 AM   #1
Registered User
1998 TJ Wrangler 
Join Date: Mar 2011
Location: Topeka, Kansas
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   Reply With Quote Quick reply to this message
Unread 02-27-2013, 07:57 PM   #2
Registered User
1987 YJ Wrangler 
Join Date: Dec 2009
Location: Mooresville, North Carolina
Posts: 111
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.
mncdriver is offline   Reply With Quote Quick reply to this message
Unread 02-28-2013, 05:49 AM   #3
Farm Wheeler
2000 TJ Wrangler 
Join Date: Apr 2005
Location: Elkmont, AL
Posts: 10,050
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   Reply With Quote Quick reply to this message
Unread 02-28-2013, 07:36 AM   #4
Registered User
1995 ZJ 
Join Date: Mar 2005
Location: , Suffolk, NY
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

Less than 8 is like playing with half a deck
Long Island Motorsports Association
Evildriver-3 is offline   Reply With Quote Quick reply to this message

4.0 , 4.0l , cap , engine , oil

Quick Reply

Register Now

In order to be able to post messages on the JeepForum.com forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.
Confirm Password:
Email Address
Please enter a valid e-mail address for yourself.
Note: All free e-mails have been banned due to mis-use. (Yahoo, Gmail, Hotmail, etc.)
Don't have a non-free e-mail address? Click here for a solution: Manual Account Creation
Email Address:


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

Thread Tools

Jeep, Wrangler, Cherokee, Grand Cherokee, and other models are copyrighted and trademarked to Jeep/Chrysler Corporation. JeepForum.com is not in any way associated with Jeep or the Chrysler Corp.