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Leaky oil filler cap on 4.0L

D

Don Becker

NAXJA Forum User
Location
Beaverton, Oregon
At the rate of (I assume) heat deterioration of the rubber gasket material, I really should replace the oil filler cap about four times a year. I get-around-to-it about twice a year :bawl: . ‘Replace it and a few months later, there’s this recurrent light coat of oil on the top of the valve cover. The caps are not expensive but, I just thought I’d ask whether anyone might have come-up with a solution. Interestingly, the cap on my wife’s 91XJ 4.0L is a different design and I don’t think we have the same problem with it as I have with my ‘88XJ 4.0L. But, her hood also doesn't have the insulating blanket and isn't quite exposed to the (I'll say) intense heat as is my '88. As I type this, yes, it is occurring to me to check and see if they’ll interchange - - and, I’ll do that tonite. But, still, I would like to hear whether others have had this problem and whether you have any other solution. I did a search and didn’t locate this as having been discussed before. Blow by is not an issue with this engine – yet. Thanks! Don
 
Don Becker said:
At the rate of (I assume) heat deterioration of the rubber gasket material, I really should replace the oil filler cap about four times a year. I get-around-to-it about twice a year :bawl: . ‘Replace it and a few months later, there’s this recurrent light coat of oil on the top of the valve cover. The caps are not expensive but, I just thought I’d ask whether anyone might have come-up with a solution. Interestingly, the cap on my wife’s 91XJ 4.0L is a different design and I don’t think we have the same problem with it as I have with my ‘88XJ 4.0L. But, her hood also doesn't have the insulating blanket and isn't quite exposed to the (I'll say) intense heat as is my '88. As I type this, yes, it is occurring to me to check and see if they’ll interchange - - and, I’ll do that tonite. But, still, I would like to hear whether others have had this problem and whether you have any other solution. I did a search and didn’t locate this as having been discussed before. Blow by is not an issue with this engine – yet. Thanks! Don
Click to expand...
Don,
You might consider swapping a later model valve cover on to your 88 4.0 engine. The breakdowns are as follows...
87-90-your style, crappy oil cap and ccv elbows
91-92-your wife's style, better oil cap, better ccv elbows
93-95-the best of the aluminum covers in my opinion. Same oil cap as 91-92 models, but better 90* molded CCV elbows.
96-07-stamped steel valve cover, ratcheting oil cap (which is known to strip out but when it works, it definitely doesn't leak), 90* ccv elbows. In my opinion the best valve cover out there. I have had this style on a 90 4.0 and an 88 4.0 and have been very pleased.
I would really recommend a 93 or later style so you get the improved CCV fittings as well as the better oil cap. Be sure if you get the 96+ style you get the reuseable gasket as well. Hope this helps.
-Collin

Thought I'd add some pictures as well...
This is the 87-90 style...
Comanche002.jpg

Here's the 93-95 style...
ResizedVC2.jpg

And the 96+ style...
EngineShot.jpg
 
Last edited:
Excellent! Thanks so much! Don
 
Don Becker said:
Excellent! Thanks so much! Don
Click to expand...
No problem, glad I could help. Let me know if you have any further questions.
 
scottmcneal said:
Is that a FRAM filter????
Click to expand...
Yeah not by my choice though, that was what the PO of my MJ decided to use.
 
scottmcneal said:
Sorry, just tired.. i like the pics, it helps me out too.. thank you
Click to expand...
Haha it's all good man, yeah sad part is I got that thing about 6 months ago and it's yet to see an oil change. That Fram is still on there.
 
Now that I have a moment, I wanted to more properly thank RenixPower for going over-and-beyond in his reply to my huge, major ( :roflmao: ) problem here. I haven't been on here for awhile (the XJ's have been pretty-much behaving themselves). But, I'm surely reminded of just how GREAT you guys are! Thanks again. BTW, the caps between the 88 & the 91 are not interchangeable. I'll pick-up a new cap for the 88 this evening and keep RenixPower's great information for next time the valve cover has to come off. In the meantime, maybe I'll take a trip to the U-Pull-It to see if I can locate one of his recommended valve covers. 'Only thing is, I suppose I then have to do my posting on the Modified Tech forum :laugh2: :laugh2: :laugh2: Don
 
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