Truck has 116000 miles. At speed it has great oil pressure. After getting hot, 15 to 20 miles, at idle the oil pressure goes to nothing. Engine does not rattle no mater how long you allow the truck to idle. I have noticed the oil pressure changes as the rpm changes when the transmission is down shifting. Any one have any idea's?

 

Put a gauge on it to see what pressure really is, don't rely on an electric gauge. If in fact, your pressure is dropping to zero at idle, then you need to assess the overall condition of the engine. Will a new oil pump cure the problem or is it beyond reasonalble repair.

 

I installed the gauge on the truck. At start up the truck has 50 psi. I let it set in the drive andidle for 30 minutes.The pressureslowly falls to 10 psi where it stabilized.The oil pressure will come up to the 40 psi point if the RPM's on the truck are raised to approx 2000, no RPM needle on this truck. Is10 psienough oil pressure to protect the engine? Does the truck need a new oil pump? Is there something more catastrophic happening to the engine? This is a really nice old truck other than the oil pressure problem.