Hi everybody! Oil pressure drops to 0 on my 1989 F-250 when engine warms up. (30 PSI on cold) It doesn't happen all the time though. When it dropped last time I could hear the lifters noise. Engine sounded rough. Then it went to normal again.

It started after I changed oil and went to a little trip (about 500 miles) last Thanksgiving. Truck had an oil leak that I didn't notice and I lost a lot of oil on the way. I found extremely low oil level after 300-400 miles of driving, I don't know how long I have been driving before that. I put 2 quarters right away (a little more than it needed). When I hit the road again, oil pressure dropped to 0, engine sounded rough, but no knocking. I made it all the way back home, truck got happy and oil pressure went to normal level again.

And after 3 month here we go again. What can cause it? Gauge seems to be OK. In the service guys checked it with mechanical one. Oil pump?