oil pressure problem after starting

I have a 99 silverado with 125000k on the engine. My problem is after I start it the oil pressure drops all the way down to 0 but if I shut it off and re-start the engine it is fine for about 3-5 minutes and then it does it agian. I just replaced the fuel pressure regulator which was making it run a bit rich but would this in any way have anything to do with the lack of oil pressure?

Maybe! There's a chance that the oil might have gotten thinned out, due to the bad regulator. Try changing the oil first. If problem persists, connect a mechanical oil presssure guage to the engine and see what its reading. You might have a weak oil pump. But before we open that can of worms do these checks first.

I changed the oil, plugs, wires, and started it up and I thought the problem was solved....then the pressure went down again and the engine made a whining/squeaking sound, could that be the oil pump? I have no visable leaks and there was very little gas in the oil so I suppose it could also be the rods and or bearings??? Any thouhts?

When you give it the gas does the pressure go up?

If not:

1. Clogged in the lines. Try running two qtrs of engine flush and get the engine really hot.

2. Get an air hose and hook up the the connector above the oil filter where you put an oil temp sensor should go and blow some 175 psi in there. Had to do that once and then flush again.

3. Oil pump bad. Drop oil pan and replace.

You might want to do all three.
If you hear metal rubbing shut down.

It does go up somewhat but the longer it runs and the hotter it gets the less pressure I have.
From some of the posts that I have read I may have a bearing problem *@#$, I really hope not but I am going to try a heavy weight oil and see if the pressure will hold at idle. Oh, did I mention that it ticks a bit now at idle speed as well. I did put a can of seafoam in last night and let it sit all night so hopefully if things are/were clogged they will be better today.

I have a 81 jeep with a chevy 350.

Does the same thing.

I have a brand new High volume/pressure oil pump that is two months old.

80 psi when cold but when I hit 160 temp the PSI is 0 at 450 rpm. Hit the gas and at 1500 rpm I have 40 psi.

It has done this for 2 years. Really dry starts in the morning. Make a lot of noise.

I put in 20w-50 and the STP engine treatment and use engine flush every oil change.

I bet I am hardest on this engine than anybody has ever been on a 350 and it has not failed. I was so impress with the 350 5.7 that this is main reason why I bought a new used chevy.

Specs:
81 cj5 Jeep with a Chevy 350
Hp 400 at the wheels
Torque: 375 at the wheels.

I have broken at T-18A tranmission / Dana 300 transfer case and Dana 60 axles with this engine and lets not even talk about u-joints. THANKS GOD FOR TOM WOOD drive shafts.

Sucker is bad to the bone.

I tell everybody that if you do not have a chevy in your jeep you are just wasting time. :lol:

Dont really think you have a clogging problem, but if you had gas in the oil could of washed out the bearings. I have never hardly seen an oil pump go out on a smallblock. But i would install a manual guage first to make sure guage inside is working. The tapping is probably coming from the lifters not getting enough oil up to them. Hopefully its an easier fix than we think.