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Losing Oil Pressure

09-09-2007, 01:11 PM
I recently pulled the engine from my 1997 Blazer due to water leaking into the oil. I found that it was a cracked intake gasket. While apart I replaced the main and rod bearings, timing gears and chain, timing cover, head gaskets, valve guide seals, rear main seal, .... You get the picture.

Now I have a problem with the oil pressure. The pressure started out at just over 40psi from a cold start. After idleing for a while the pressure begins to drop to the point that I get a check gauge light and the pressure gauge reads less than 10psi.

Any ideas what could be causing this? :banghead:

09-09-2007, 01:55 PM
Welcome to AF

Are you checking the oil pressure with a manual test gauge or just going by the dash gauge?

09-09-2007, 02:19 PM
I'm just going by the dash gauge.

When the engine is cold the pressure is fine. As soon as it drops low enough to turn on the check gauge light you can hear the engine start to knock. If I raise the idle the pressure comes right back up but quickly falls low enough to turn on the check gauge light again.

I just finished replacing the oil pump again, thinking that I may have gotten a bad one from the parts dealer. When I drained the oil (which was new) it came out almost black and there was a very fine (almost graphite like) metal dust on the oil plug magnet. I ran several gallons of clean oil (changing the filter each time) through the engine until the oil was clear again.

09-09-2007, 02:30 PM
You put in one of the bearings wrong. It is typicle of cam bearings but you did not say cam bearings. Did you check journals before replaceing bearings ?

09-09-2007, 02:38 PM
Didn't replace the cam bearings. And the (crank) journals all checked out within tolerance.

I'm not sure how I could have put in one of the (main) bearings the wrong way, they seem to only fit one way. As for the rod bearings, both halves are identical.

09-09-2007, 03:01 PM
Like MT said check your oil pressure first with a manual guage. If bad I would guess one of the bearings.

09-09-2007, 03:49 PM
Yeah, I'm also thinking that it's a bearing. I was just hoping that I wouldn't have to pull this thing again. :crying:

Any other ideas come up please feel free to post them up.

One other question...
Should there be a gasket between the oil pump and the rear main bearing cap?
I don't remember taking one out and I've tried running with and without a gasket and have the same results either way.

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