Hello. I have an oil pressure issue I can't seem to figure out. I've recently rebuilt a '96 6.5L that was in sad shape mechanically. It was bored .030 with new pistons/ rings, new heads, good polished crank with stock grind, cam checked out fine and new bearings installed. The block was magnafluxed and all the bearings and gaskets were replaced along with a new oil pump. The cooler was flushed out. The engine has Rotella 15W40 in it with a Hastings filter. The machining was done by a very reputable shop in our area. While putting it together we plastigauged a few of the bearings and found all was good. The turbo has a good feel to it with no movement and free spinning. I know the oil plugs in the block beside the cam are installed. That should cover the history on it.
We primed the pump and fired it up. We had about 40- 45 pounds immediately and it ran good. As the engine warmed up (about 15 minutes run time) the pressure kept dropping off to around 10 PSI while the temps were up around normal operating range. I installed a mechanical gauge connected to a T in the turbo supply line and restarted it. The mechanical gauge showed 8 PSI at idle warmed up. We started looking at possiblities and found that the 2 bypass valves above the filter were removed at the machine shop and neither of us had reinstalled them. New ones were ordered and we installed them along with the correct frost plug. I thought for sure it would be taken care of, but instead our cold oil pressure dropped some to about 30 PSI and we're still dropping off to 8# warm at idle. It will come up when the engine speed is increased, but only to about 30-35 PSI.
I have not driven the truck yet so the oil has not been hot even during our checks. I am wondering if we don't have a faulty oil pump and am about ready to pull the pan to try it, but am not looking forward to that.
Would anyone have any suggestions or thoughts in figuring this out. Thanks in advance. It is greatly appreciated.