Low Oil pressure when hot

[Ra1994gh]

Sorry for the late reply but I did not have the chance to work with the car before today. So I changed the oil filter with a MAN filter, changed oil to 20w-50 and installed the manual gauge and on cold start idle the pressure rises to 30 psi quickly. As the oil gets hotter the pressure drops and it drops all the way down to 1-2 psi fully warm. And 2000 rpm roughly 10 psi and 3000 rpm around 20 psi. I am starting to think that either main bearings or rod bearings may be my issue or both. What should be my next move? Can I inspect them or change them by only getting the sump off while still having the block installed?
and what should I look for?

[digger]

That doesnt seem good at all.

Thinking out loud you might get lucky if you can pull the pan and check the pump, the separate relief valve and even the rod bearing clearance with plastigauge in situ.

Checking the mains in situ is not as accurate in the car but can work around that but if they are the issue its an engine out job whereas the other stuff potentially in car / in situ replacement may work depending on the root cause and consequential damage if any.

The intermediate shaft bearings can be checked by removing the belt etc and feeling for play or measuring with dial indicator and/or removing of the shaft to measure bearings in situ if you have a small gauge

[Ra1994gh]

Thanks for the reply. So to make it clear, the pump has already been replaced with a working pump and I have inspected them both internally and they seem to be in good condition. Even when I turned the pumps manually driven with a drill connected to the rod on the top I could feel pressure and see oil spraying. Also now when the car was running removed the oil cap on the valve cover and I could see oil spraying and lubricating the camshaft.
But for now I will remove the oil pan again, and remove the oil pump to get access to the main and rod bearings. Then what should I do exactly?
I still have the old bearings never threw them out. Should I compare something or measure clearance while the new bearings are still installed?
could I have installed something wrong down there? Even though I remember they had a knot so they should only be possible to mount one way?

[digger]

The reason for pulling the plan is the slim hope that it isn't bearings

are you running the standard oil pressure relief valve? you can check it isnt stuck open or something maybe?

Regarding brgs you can check the P/N of brgs and if you have plasti gauge strips you can measure the actual clearance but really only works accurate on rods since main bearings are loaded in the car

[Ra1994gh]

I am running with the standard oil pressure relief valve. Someone wrote once that you can actually delete it at get a plug to screw in instead?
but I am doubting that because I also changed that with the one from the working engine just to be sure.
Could I change the bearings with the old ones laying around just to make it running again for now? Even though they are not in order? They are mixed and not marked for each cylinder.

[Ra1994gh]

I could get a plastigauge kit from kolbenschmidt and measure the rod bearings as you suggest. But what should the clearance be?

[digger]

I am running with the standard oil pressure relief valve. Someone wrote once that you can actually delete it at get a plug to screw in instead?
but I am doubting that because I also changed that with the one from the working engine just to be sure.
Could I change the bearings with the old ones laying around just to make it running again for now? Even though they are not in order? They are mixed and not marked for each cylinder.

Apparently you can delete the isolated relief valve and just the one integrated into the pump but I wouldn’t do that as 100,000s engines run ok as per factory setup

don’t randomly change parts it doesn’t help find root cause and you can’t change mains in situ practically speaking ( not physically impossible though)

basically the thinking is you’re oil system has a massive leak path and that is why the pressure is low. If the oil delivery is good (pump) and the mating of pump to block is good, the relief is good and you haven’t forgotten to add some plugs or other oil system components, no partial blockage, then oil is leaking from either main, rod or intermediate shaft bearings at a much much higher rate

If you have a Bentley manual you should find specs but it is in the order 0.0012 to 0.0025 iirc . You are looking for accidently using standard bearings when oversized should have been used check p/n (should be same as originals if crank not ground) , somehow clearance numbers way way above the max spec-or massive wear marks. The other is intermediate shaft bearings breakdown which you don’t need to pull pan to check for

[zaq123]

if you had 1-2 psi, I'd say pull that engine and really go over everything to find that issue. You can drop the oil pan and unbolt rod caps to take a pick at those bearings. I have a feeling they won't be looking too good after seeing 2 psi oil pressure with any normal engine load on them. You never answered if the block was hot tanked before the rebuilt.

[Ra1994gh]

My idea was to take off the pan, inspect bearings at rods and try to take one main bearing off at a time to inspect, because I don’t want to remove the head again since I am seeing oil going up there and everything in the head has been rebuilt at a professional shop.
I will take pictures and report back to you guys. Thanks for now.
I really dont know what hot tanked means?

[Ra1994gh]

I just googled the hot tanked , and if that means that if the block was cleaned inside a hot water batch kind of way, then no. It was put on an engine stand to drip off the excess oil but nothing other than that. The engine was working before and nothing wrong so therefore I did not see point of overdoing it. I just painted the outside black heat resistant paint after cleaning with a wire brush. Nothing else.