Oil gauge question

[Muskratt2]

On my 89 C1500. After the motor is warm the oil gauge will go to 0 & the check gauges light will come on. This has been going on since I bought the truck almost a year ago. I have changed the sending unit but my mehanic says I'm using to thin of an oil (5w-30) & need to go to 20w-50.
The motor is quiet as a church mouse & doesn't rattle or knock.
My question is, was there issues with the gauges on these trucks & that could be the problem?

 

[90W7]

If the pressure truly dropped that low you would hear it In the valve train.

So you put oil pressure sending unit in and it didn't help at all or change anything?

 

[Muskratt2]

So you put oil pressure sending unit in and it didn't help at all or change anything?

That is correct. That is why I wonder if it's the gauge. I thought I had heard or read one time those gauges were known for having issues.

 

[90W7]

As much of a pain as it is you might want to T-into the oil pressure sending unit with a mechanical gauge temporarily or permanently, just to verify the correct pressure.

I agree with bumping up the oil viscosity especially in higher mileage engines however 5w-30 won't make your gauge zero out like that.

I think that would be the best bet to tell if it's the gauge or a mechanical issue.

 

[98_k1500]

I'll bet the pressure is actually doing it. "after the motor is warm" is a dead giveaway. May wanna run 10w40. There is no need for 20w50, that stuff is entirely too thick and can starve areas of the engine for oil on startup. If the pressure comes up when you give it a little throttle, i would run 10w40 and run it until it quits. I have seen a vortec 350 doing the same thing. To my knowledge its still running. If it don't spike with throttle, i would say its days are numbered. Sounds more like a worn oil pump to me than bearing issues.