Help!!!! 1985 Blazer 2.8 with complete rebuild but it loses oil pressure after it warms up. Is there a problem with the oil gallery? Or perhaps a crack in the Block. Surely someone out there has had this problem. I have used a seperate oil gauge to double check the numbers. Oil pressure is 50 to 55 lbs when engine starts the nose dives when engine gets warm. It has new rings, new mains and new rod bearings. New crank with three new oil pumps. Should I just sell it for scrap and live with the stranded cost. TAD

 

I'd say there's a problem with the work that was done.

What you're describing is a dropoff in pressure when the oil warms up, so it's related to the drop in effective viscosity when the oil gets warm. That means there's some spot with wide clearance that holds pressure when the oil is cold oil and thick, but allows pressure to drop when the oil warms up.

If it were something simple like a bad oil pump, it ought to be same cold and hot - but it's not.

I'd say the fix is to pull the motor, open it up and go through every part that was worked on. Plastigage the mains and rod bearings, and look carefully for a rod or crank journal that's not flat. I'll bet that's where the problem is...and I suspect the new crank is the problem.

This is a pain, but better than losing the money on the work that you've done.

Maybe someone else will have another thought....I admit I don't understand "three oil pumps". Do you mean you've changed them out and tried three different pumps? i don't think that's the problem in any case.

 

What do you mean by nose dives?
Does it drop to like 40psi and stay there?
Does it go back up when you give it gas?

 

this is actually a repost. i responded to his other thread and he emailed me with more information, didn't get a chance to respond to the email -

 

You have to have a bearing not right. Its possible to easily do this. Cracked block more likely to have water problems. If you are not getting water in your oil then this is not it.

Of course I do have a CRITICAL question: Was the block properly cleaned and oil passages are clean? Have the lifters been replaced or not?


Many folks will check a couple of bearings with plastigage and assume the whole engine is the same. It is entirely possible for one rod or one main bearing to have been up to 10's of thousands off to begin with and if it was not checked with the plastigage properly, then it may well be way off now. In other words, if you kept the same crank, one of the OLD bearing might have been replaced previously because of a regrind, with an oversize different from the rest. GET IT?? I know YOU got new one. The preceeding is for others.

I have even seen cranks with kits purchased that had one not correct. The problems happen to slip by the inspectors and so what if your engine blows up. Not right is it? How about when you purchase a set of bearings and one or two are not the same as the box says on it. If every bearing is NOT CHECKED, then this is where the problems show up. What if your kit got standard bearings and should have got +10? That alone on the mains would do it. You'd be amazed what the parts houses are capable or incapable of.

Now why would anybody in their right mind ever plastigage a complete crank and bearing set????????????????????????? Cause you should.

Heck I'v seen brand new cranks that couldnt be turned properly by a starter cause they wobbled at the gear, were simply not straight enough. Perhaps dropped or something.

Some of the above reasons is why I ended up getting a frame to mount motors in and starting them up long before installing them.

 

Hey Blazingsaddle.
You sound like the man I am looking for. Look for a thread in teh engine section on a '93 engien rebuild.

 

I did look, could not find it. Send me a link?