GM-GMC: No oil pressure, oil pressure gauge, chev truck

Question
I have an 89 chev truck. I drive it for 10 min and then the oil pressure drops to 0. I have changed the spark plugs, oil, filter and sending unit but it still has this problem.The truck has 160 000km on it. Sorry its not a diesel question but you were the only one i found to ask this question. Any info would be greatly aprreciated Thanks

Answer
There are a couple of possibilities:

The oil pressure gauge could be bad.  A known-good mechanical gauge should be installed to verify what the oil pressure really is.

Make certain that the engine is not overfilled with oil.  If it is, the crankshaft will beat the oil into a foam and the oil pump cannot pump foamy oil.

The oil pick-up tube on the oil pump may have vibrated loose and fallen off.  The oil pump will still work, but as the engine runs, the oil level drops until the pump inlet is no longer submerged.  The pick-up tube is installed such that it will draw oil from near the bottom of the pan.