Oil pressure reading

[criche1]

I need some help. I have a 2000 GMC Z71 with a 5.3 and when it is cold in the morning (below 50 deg or so) the truck starts fine but the first time I come to a stop sign, the oil pressure slowly drops to zero. If you tap the gas, it comes right back up to 20 psig, and the problem goes away once the truck is warm. I replaced the oil pressure sending unit a few weeks ago, but it still happens. I talked to a mechanic yesterday and he seems to think it could be an oil pan screen clogging up, is this a possibility? I am embarrased to say I have been using aftermarket filters since I bought the truck in 2002, could this have something to do with it? The truck has 170,000 miles on it, so I wouldn't be suprised if the oil pump needed to be changed, but the pressure stays between 20 and 60 psig when it is warm, so it seems like that is fine. Any help would be greatly appreciated.

[GM-Tech]

That's unusual. Usually, it's the other way around when there's really an oil pressure problem. That is, pressure is good when cold but drops as the engine warms up and the oil thins.

 

I'd want to put a mechanical gauge on it to see if it's really an oil pressure problem before I started digging into it.

[criche1]

I don't know if it makes any difference, but I had the entire instrument cluster replaced about a year ago because the dealership thought that was the problem, but they never put a mechanical gauge on it (they said they didn't have the right fitting, I find that hard to believe). Is there anything else in the reading system besides the sending unit and the gauge that could go bad? Thanks for the help.

[GM-Tech]

Is there anything else in the reading system besides the sending unit and the gauge that could go bad? 

 

The wiring that connects it all together, but it doesn't sound like wiring if tapping on the gas causes the pressure to rise with rpms.

[criche1]

I think I'll test the pressure and if it's in spec, I'll just let it go. Thanks for all your help.

[WI_Dave]

I think I'll test the pressure and if it's in spec, I'll just let it go.  Thanks for all your help.

 

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I wouldn't let it go just in case something does go wrong later you'll never know.

[criche1]

Then what should I do? I don't want to bring it to the shop unless I have to, I need my truck every day and my wife works too. Do you have any thoughts on what I can do myself? I am pretty mechanically inclined and have already fixed quite a few things on this truck, so I am open to anything. Thanks for the help.

[GM-Tech]

First, check your pressure with a mechanical gauge and determine if in fact the pressure goes to zero on cold starts.