Tractor Repair: Low oil pressure after exteneded running, oil pressure gauge, low oil pressure

Question
I have a Case-IH 695 that has a newly rebuilt motor last fall. I don't run it too hard and rarely over two hours at a time. I notice the oil pressure is good at start up and stays up above 50 lbs.  I noticed that when I ran it for extended hours and the temperature is aove 90 degrees, my oil pressure gauge shows no oil pressure and the needle vibrates excessively. The oil pressure light did come on and I shut it down and after it cooled I checked the oil and it was just below the full mark. The tractor's water was elevated but not in the red. Do you think this could be a oil pump failure or defective oil pressure gauge? (The oil line to the gauge is a very small nylon type tube that comes off the top of the oil filter. I had changed the break in oil and filter before noticing this problem). Or could the dipstick be wrong and there isn't enough oil in the crankcase? Alan

Answer
Hello,

  First, screw in a 100 psi diagnostic pressure gauge and hose right on the engine where the nylon tube is attached.  You may need to remove the fitting from the engine and put in a different one to adapt to fit the hose.  This will verify if it is a gauge issue or not.  If it still shows low pressure, check that the oil is the correct viscosity and is not too thin, and that the nylon tube is not pinched or kinked anywhere.  If it's OK, check the oil pressure regulator valve, oil pump and crankshaft bearing clearances.  Even if the dipstick was wrong, it wouldn't be off by that much that the oil level would be too low for the oil pump pickup tube.