I bought a 2001 NB that had overheated. I pulled the engine and rebuilt it. The crank was within spec as were the rods. I had to install new pistons and all new bearings. The head was rebuilt. I also installed a new oil pump and pickup tube.
It started right up, which was great! However, I put an oil pressure guage on it to ensure pressure was good. But its not. I have 10w30 Castrol oil in it. At cold startup, it has about 50 PSI at idle and accelerating will raise the pressure to 60 PSI. As it warms up, the pressure drops to 20 pounds at idle.
I used plastigauge on the camshaft to ensure there is no excessive clearance there. I did not do this on the crank. At this point I think I have to pull it out and apart to try to find the problem.
Anyone have any ideas of something else to check before I do this? I tried two pressure gauges on the engine - same result. Also two oil filters - no change.
And what does a manual say it should be??? 20# at idle hot is OK, the low pressure switch tudns the light on at arround 5#, and 50-60 at running speed is shurly ok!
Earl
Mine is between 20-25 psi (according to a $30 VDO gauge) when the oil is up to operating temp. It has 85K on the engine and oil changes always done every 3K miles.
Just pulled everything oil related off, checked, reinstalled, and added a second pressure gauge. Now I have one gauge going into the filter and one coming out. They both read about the same - still about 50 PSI at cold startup. Didn't let it warm up, but am assuming that it will drop again.
I checked the oil galleys and they are unobstructed. Checked everything on the oil filter flange and it is working well. At this point, if I only have 50 PSI coming from the pump, I can't expect more. So I believe this pump to be defective. I will order a replacement on Monday and see what happens then.
Quick update. I thought more about it and thought it practically impossible for a mechanical oil pump to go bad. I also deduced - after talking to others - that a weakness in the system after the filter would cause the pressure at the filter to drop.
Based on this, I pulled the engine and took it apart again. No apparant issues to be seen. Used plastigauge on all main bearings and they are all at about 0.00175". The big end of the rods were checked by a machine shop, so I assume they should be fine.
Now I am wondering if there isn't a crack in the case? I will sleep on it and tackle it again in the morning...
You have probably already checked this, but just in case - the oil pump has a pressure relief valve set at 175 psi. If it is defective you might not get the correct pressure.
You have probably already checked this, but just in case - the oil pump has a pressure relief valve set at 175 psi. If it is defective you might not get the correct pressure.
That certainly is a possibility. I loked at it and it seems ok. I ran the pump by hand in a bucket of oil with a drill and it seems to be pumping plenty of oil. If I can't find any other issues anywhere, I will try another oil pump. Probably should have done that first, but it just seems like a very remote possibility.
Update for you folks. Pulled the engine out and apart again. Took the block, crank, and rods to a machine shop. They speced it thoroughly and said everything is fine.
According to the Bentley manual... if you have the proper specs on bearings and such but still have low oil pressure replace the oil pump. I think I would just run a straight 30 weight oil and see if it maintains pressure at hot idle.