After the head gasket was replaced I noticed a problem with the oil pressure gage. When the jeep was started cold the oil pressure was about 40psi sometimes 50. However when the engine was warm it would drop down to 10 PSI. After a few days I noticed while sitting at a stop light that it was dropping to 0 with the check gauges light on.

Now the valves did not go flat and the engine sounded normal. I finally changed the sending unit on Friday. This didn't help any the gauge still drops after the engine is at running temp.

I changed the oil and filter again just in case the filter got plugged up with junk left from the head gasket change.

Again there was no change. Since I felt this must be a fluke I continued to drive the jeep. As a Chief Officer of an Ambulance service I was requested on a call today and needed to respond. When I returned to the vehicle after it had been sitting about 20-30 minutes I could hear the exhaust had a slightly different sound.

I am preparing to replace the oil pump in the morning, but I wanted to make sure that there was nothing else this could be. It just seemed funny that prior to the head gasket change there was no problem but just after this started to happen.

Is there anything I could have done wrong during the head gasket replacement or is it the pump??

It may be that you were struck by the gods of coincidence, in that the oil pressure reading started acting up right after the gasket change.

Can't hurt to change the oil pump.

Keep in mind two things: (1) Oil pressure generally rises with rpm -- the more you rev the engine, the more pressure you'll see. (2) When the engine is cold and the oil is thick, you will often see a higher oil pressure than you will after it warms up and the oil thins out a little.

I have known several engines to have oil pressure drop to as low as 10 psi when idling a warm engine, yet everything works ok. If your lifters are collapsing, then it's time to worry.

Before the gasket change, what was the oil pressure on an idling warm engine?

The oil pressure really never fell below 20 and would always rise back to 40 with higher RPMs. I did notice a few times prior to the head gasket change though- there were times the oil pressure went to 60 when cold sometimes higher but would always drop back to 40. It never went all the way to 0. Now when at idle the pressure is 0 and at 2000 RPMs it is 20psi. On the highway at 2500 3000 rpms maybe 30psi.

Is it possible that when the oil and water were mixed it could have damaged the pump?

I don't think that's too likely, but I suppose it could happen. If you're sure that the fault is not in the oil pressure measuring system, I'd go ahead and change out the pump.

Thats the problem I am not all to sure. I think I am going to buy a pressure gauge and check it manually. I will let you know tonight.