mjeff87 Posted March 29, 2007 Share Posted March 29, 2007 Bottom line is my MJ has excessive pressure under the valve cover...and I mean excessive....to the point where oil is being forced out under the oil fill cap gasket (don't even ask about how soaked the air filter is, either :oops: ). I've done all the PM checks on the CCV system (repeatedly), and the baffle inside the VC, and it's working as it's supposed to. I've also run a compression check and have strong #'s in all 4 (I was pleasently surprised at that at 170K miles), so I'm assuming it isn't blowby past the rings. I am going to do a leakdown test next as a follow up to the compression test, and am going to remove the VC when I do it to see if I can see/hear air escaping anywhere. If that doesn't discover anything, I was planning on replacing the oil seals while I had the cover off, to eliminate them as another possible cause. Has anyone here replaced the oil seals on a 2.5 (with the head still attached)? If so, any tips/tricks or any words of wisdom you could pass along? Anyone have other advice? TIA, Jeff Link to comment Share on other sites More sharing options...
Pete M Posted March 29, 2007 Share Posted March 29, 2007 Catch bottle for the oil. :D Link to comment Share on other sites More sharing options...
mjeff87 Posted March 29, 2007 Author Share Posted March 29, 2007 yeah Pete, I could do that....but if I can fix the cause it'll give me peace of mind. The way I figger it, positive pressure under the VC can only come from a couple different places, either bottom end or top. Since I'm fairly certain (will confirm with the leakdown test) it's not from the bottom, it's gotta be the valve stem seals, but I've never messed with that. I've got a complete spare 2.5 that's gonna get transplanted in sometime in the future, but for now I just want to see if I can help this one along without too much fuss or $$$$. I'd love to get 200K on it before I pull it :D Jeff Link to comment Share on other sites More sharing options...
Eagle Posted March 30, 2007 Share Posted March 30, 2007 But valve stem seals are NOT "seals." They will not prevent pressure bleed, but I don't think that's the cause of your problem anyway. The proper name for valve seals is "deflectors," and that's all they are. They're little plastic umbrellas that just prevent oil running down the valve sten. They don't provide a positive seal to anything. Link to comment Share on other sites More sharing options...
jaekl Posted March 30, 2007 Share Posted March 30, 2007 My oil leak/blow out was a clogged vacuum line. On my 86 it was the one on the front left side of the engine. The metal tube was clogged tight. Oil was coming out everywhere until I opened the vacuum line. Link to comment Share on other sites More sharing options...
mjeff87 Posted March 30, 2007 Author Share Posted March 30, 2007 The whole CCV system is clean as a whistle (the front clean air hose from the airbox to the VC is new to boot), and I've got great vaccuum in the rear line....so I know it's working right. Eagle, if the pressure isn't coming from blowby past the rings, where in da 'ell is it coming from?? IF you take the fill cap off while running and hold your hand above the opening, you can actually FEEL the pressure pulses. I'm stumped on this one. Other than that, it runs great. I just have to wipe off the exccess oil off the VC every time I drive it :mad: and I'm going thru filters like Grant took Richmond (I can say that....I live here :D) Jeff Link to comment Share on other sites More sharing options...
WNC_MJ Posted April 14, 2009 Share Posted April 14, 2009 Similar problem here, but with my '88 4.0L ... air filter is SOAKED with oil and I'm losing about 1/2 a qt every 100 miles. I've checked and the ONLY leak is from my front vent. Link to comment Share on other sites More sharing options...
mfpdm Posted April 14, 2009 Share Posted April 14, 2009 Jeff I've got the same problem with to much pressure and blowing it out the oil cap. Only thing different is that it's not going into the filter. I've yet to do a compression test but the darn thing runs pretty smooth. I pulled the valve cover when I got it and cleaned it all up so I know their is no clogs there and I replaced that vavle/filter thingy on the rear of the cover. I've recently started to see moisture in the oil in the form of the tan-ish foam. This is making me believe I may have a crack in the block or head, which if I'm thinking right could cause un-wanted pressure under the valve cover. Or am I out to lunch on this. :dunno: :cheers: Link to comment Share on other sites More sharing options...
Eagle Posted April 14, 2009 Share Posted April 14, 2009 Guys, how does oil get from the valve chamber back to the crankcase? A: It drains back by gravity, through oil drainage passages through the head and block. Which means the valve cover chamber is essentially the same atmosphere (certainly the same pressure) as the crankcase. If you have blow-by at the rings, that'll pressurize the crankcase and there's nothing to prevent that pressure from simultaneously pressurizing the valve cover chamber. That's why the CCV ("CrankCase Ventilation") system connects to the valve cover, not down somewhere near the bottom of the block. Link to comment Share on other sites More sharing options...
bigd44889 Posted April 14, 2009 Share Posted April 14, 2009 blow bye at rings bad valve and yes 2.5's like to crack heads thay have a week spot i found 3 used heads when i rebilt my motor and thay were all cracked gave up and got a new one Link to comment Share on other sites More sharing options...
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