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post #1 of (permalink) Old 10-17-2000, 12:45 PM
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AMC V-8 Oil pressure issue - Weird

OK - Here's a weird thing that happened to me over the weekend...

I've been working on the Jeep body for like 6 months now, and the Jeep keeps going in and out of the driveway, garage etc. So I'm thinkg, "You know, I should run this thing for a while to get any condesation out of the engine."

Now, the negine is a brand new rebuild from RECON, it is about 8 months old, but has only about 500 miles on it - has worked great and has 25 psi at hot idle, 60 at 2500 rpms - the timing cover was on the engine when I got it and oil pump installed. I know you're all thinking, "Oh man, I know where this is going... but read on..."

Anyway, so this things idling away in the driveway for about 15 miuntes, it had warmed up, and about the 5th time I looked over to check the oil pressure, there's nothing but about 5 psi or less. So I tap the gas a little and no improvement, so I shut it off and threw up all over the driveway. No, not really, but that's about how I felt at that point!

I pulled a more "detailed" oil pressure gauge off another car and put that in and I had 8 psi and that's it no matter what the rpm. So I'm picturing either A) trashed oil pump housing, or B) trashed crank - a.k.a. engine. It was filled with Mobil 1, so I wasn't in a total panic yet - I was actually HOPING for the oil pump at this point!

So next, I pull off the oil filter and cut it up to check for metal. There's a little, but the usual amount - there's always a little tiny bit in there - I cut all of mine open mostly just so I can say I do... Anyway, there was nothing out of the ordinary here.

Next, I pulled out the oil pressure relief spring - I thought maybe it was broken, but it was not and seemed VERY springy - stuck out of the housing like 3/4" uncompressed. So then I dropped the bottom off of the oil pump. The gears looked good - very minor scratching on the outer edges. The aluminum walls were marred up - maybe even more than the 200,000 mile cover I pulled off the old motor and still have. So then I got that out and compared and there was definately more than my old one, but still what I'd call "normal" for an AMC. Oh - I forot - I did blow air back through the gauge feed line when I replaced the gauge - that was not it...

So anyway, now I'm just scratching my head, and I'm kind of done diagnosing unless I want to go to the store because I cut up the oil filter. But I wanted to mess around some more, so I took the OLD oil filter bottom cover plate, which still had the OLD pressure relief valve and spring in it, AND the old oil filter still on it, and bolted that on and cranked it up.

WALA - 25 psi hot idle, 60 psi at 2500 rpm - just like it was, and I drove it around for 30 minutes with no change and let it idle in the driveway for another 30 minutes - no change.

Want to explain that? The oil pump cover plate I took off had nothing wrong with it I could see - let's face it, there's not much to it... I don't think it could be a filter failure - I had a Fram come apart internally a few years ago and never knew until the oil change, so that can't be it. The only thing I can think of is the pressure relief valve. The only OTHER THING is that the pump drive gear could be put back in 7 different ways, but they don't wear in like that I don't think, and anyway - it's either good or bad - rotating it one tooth can't possibly make a difference like this - I don't think so anyway.

I'd like to at least know what it was - kind of bothers me, but not nearly as much as when I only had 8 psi!

Chuck Hadley
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post #2 of (permalink) Old 10-18-2000, 01:28 PM
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Re: AMC V-8 Oil pressure issue - Weird

i wonder if the pump just needed to be reprimed from sitting so long. the only other thing i can think of is the relief valve you mentioned sticking open.

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post #3 of (permalink) Old 10-19-2000, 08:58 AM
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Re: AMC V-8 Oil pressure issue - Weird

Hmmmm - I really like that priming theory maybe, although it had oil pressure at first... This is still very weird - but I've been running it daily ever since and it's got oil pressure galore! - Like I said - weird...

Chuck Hadley
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post #4 of (permalink) Old 10-19-2000, 11:50 AM
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Re: AMC V-8 Oil pressure issue - Weird

maybe it had an air bubble that couldn't get out. that would account for some oil passing through the pump.

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