We bought a 1991 Winnebago chieftain with a 460 Ford motor.
when cold it has 50-60 oil pressure. When it gets warm oil pressure goes to 0. We put in rear and main bearings. Put back together bottom end. Primed oil pump 60 oil pressure. Start engine when warm back to 0. Oil system does have an oil cooler. Also pressure relief valve by filter. It looked good. So next we took bottom apart put in new oil pump high performance. Back together. Primed oil pump to 60 Started motor. When warm 0 oil pressure it drops to. We let it set all night. Started it this morning no oil pressure. It has 15-40 oil in it. The motor had sat 9 years. The engine only has 29,000 original miles on it. We need help. Any ideas where to go from here ???

 

Something changed from the time I read the post to the 1 minute later when I was about to ask a question and that was the gauge readings and what gauge that you are using.

Anyway, my first question is; are you using the dash gauge that relies on an electrical sending unit or have you actually verified the oil pressure reading with a physical gauge? Both types are good practice when there are such huge discrepancies. What say ye ?

 

We have put both on. It’s good for about 25 minutes then oil pressure drops to nothing

 

It’s about 15 minutes not 25.

 

Whatever is happening is affected by temperature and I find it pretty difficult to believe bearing wear could change the reading that quickly..
What can do that is the relief valve (by-pass) that might be hanging up after it gets hot enough. When you say it "Looks good" , were you able to see ANY score marks or other possible irregularities, that could cause it to hang up? It should be absolutely smooth and without any marks.
Have you checked to see if any oil has found it's way into the cooling system?

 

No oil in cooling system. The oil pressure relief valve is on a part that hold the filter and two lines from oil cooler. It’s an 90 degree adapter we had to take that piece to machine shop to get the bolt out where the spring and ball is

 

I hate to tell you this, but I believe that is where the problem lies.

 

I thought that the oil relief valve where it is located just by passes the oil filter. But it should have oil pressure if it’s by passing. So you are telling me that if that is open or stuck open we will not have any pressure. We put drill on oil pump and it lets oil come out oil sending unit hole but when we put it back on there is no pressure We took the adapter to machine shop. We couldn’t get the valve open. They got it undone. I wonder if they did that by heating it and the spring is very weak now. Is there any pics that show how the oil flows.

 

I believe you are correct on this. I was not aware of the oil press problems until I did a little homework and there is quite a history of bearing problems and oil pump changes , hardened dist drive shafts for the higher vol oil pumps and so on. Unfortunately, I am behind on this and hopefully someone with more knowledge on this will come forth and offer some better answers.

 

Taking pan back off and looking at oil pump again. This has been such a problem Hopefully we will have some answers today. Is there any other place on a 460 that has an oil pressure relief valve? We are hoping we got a bad pump and can replace it.