1. Well, the tapping upon gauge loss of oil pressure indicates that it really is low oil pressure.

2. Most oil filters have a bypass that lets oil around the filter when the filter can't pass enough. So unless you specially bought a filter with no bypass, it isn't the filter.

3. I've never heard of gunk INSIDE an oil pickup tube

4. The scenario of stuff clogging the pickup SCREEN is plausible.

5. ALL commonly sold motor oil has detergent in it. So the idea of a "detergent" oil cleaning up an engine that had only been run on "non-detergent" motor oil is just plain wrong, unless one is starting an engine that hasn't been run for more than a half century.

6. Diesel lubricating oils have high levels of detergent because the oil carries a truckload of soot

7. My initial diagnosis was sticking bypass valve in the oil pump. That would explain the on/off nature of your problem.

8. DO change the filter first, it is inexpensive and easy to do. Then drive the truck and see if it happens again.

9. If that doesn't work, you have to drop the pan. While you're in there, change the pump. I have wasted two engines because I didn't change the pump. The original oil pump looked fine, but once engine warmed up, oil pressure went to around 5 psi.

10: To check the condition of rod and main bearings, look at the #1 main and the #1 rod journal. As these two bearings get their oil last, they are the first to go. My second 318 crank is reusable except the underside of the #1 throw is terribly ground down. The #2 rod bearing was perfect. On the same rod journal I had both no wear and extreme wear.

11. One of the culprits I see here at work all the time is shuttle valves sticking because of varnish buildup.

R.

R.