Ok, so I have had great oil pressure considering my truck has 186k, ticks but otherwise runs fine, actually runs really well. I replaced the front cover / oil pump 2 years ago and pressure is consistently 52 psi at cold start then settles in at 40-45 psi hot @ 2000 rpm and 12 psi hot idle. All in spec. I have a oil pressure gauge so I can see it realtime. Yesterday morning at first start my oil pressure light AND gauge indicated zero until I turned it off, about 15 seconds later. Until then the factory light would go out in 1-2 seconds and the gauge would jump to 52 psi immediately. So, thinking I finally lost my engine, I restarted it and it was back to my normal and has been for the driving I have done since. Since both the gauge and factory light indicated low or zero I figure they confirmed its not a bad sensor as they read from different ports. Is it possible that the oil pump or feed system can drain out or get air causing the pressure delay? Randomly? I started it this morning and it was fine.
I do like trucks that can fix themselves so if that's what happened I am OK with it.

 

Could be a bad filter, some gunk on the pickup or just a temporary clog. When did you do your last oil change ?

 

Good thoughts. Oil change was this spring. I did use a cheaper Fram filter this time so that might be it. My oil stays surprisingly clean and doesn't really lose any between changes with no serious oil leaks, which is not normal. Just some valve cover weeping.

 

@dswilly mine was great for a few years but all that off road stuff seems to loosen stuff up - I lose maybe a liter over 6 months.

 

Do you mean silly off road stuff like this?

 

Fram filters are absolute garbage. I wouldn't run one on a free lawnmower. Get that garbage out of there and put something good on there.

 

Yeah, I think that's on the list. It happened again yesterday. I started it, all OK, drove the front up on ramps to pull the front drive shaft to regrease. Finished that up, started it and had zero pressure. After several on/off cycles it jumped back to normal and was fine this morning. I have a extra front cover and was looking at it last night. From what I can tell -

If it was the oil pump, it would be low or zero and stay there I think unless I am missing something. My front cover / oil pump is new < 7k miles. When I changed that, I replaced the small o-ring in the oil filter adaptor with a match from the local auto parts store. My thinking is that might have deteriorated and cause the cavity above the oil filter to drain out or lose pressure, and will get worse over time. I ordered a new OEM one today. OR the Fram filter is acting up, relief valve sticking open or other issue. So I will replace that and do a oil change and see what happens.

 

Yeah, that's where I'd start too. Oil change with a Mann or Mahle filter and Rotella 15W-40. My truck is on its third oil pump (127k on it) due to weird oiling issues like this, so I feel your pain

 

My two cents: Sounds like a sticky relief valve, stuck the bad way. Maybe pops open with initial cold high pressure, then hangs up. Not too hard to open up and check, anyway.

 

That's a good assumption. If I understand how it works, and it hit a high cold start psi, I would think my oil pressure gauge would first come up to pressure then drop suddenly. Maybe it doesn't read that fast. I have the old front cover to use as a guide. On that one I removed the snap ring but can't figure out how to get the spring and valve assembly to pop out. I could switch them if needed. Started fine this morning, all normal.