Low oil pressure on 4.3 Vortec

[stutaeng]

Hi guys, I need some help on a 99 Silverado with the 4.3. Over the winter I had noticed my oil pressure gauge on the dash was lower than normal. It is summer now and reading zero at idle when it's hot outside (100F, Dallas, TX)

I hooked a mechanical gauge and it reads 6 psi at idle. There seems to no be a spec for idle pressure?

I compared to Haynes manual at this is what I got:

1000 RPM - 11 psi

2000 RPM - 27 psi

4000 RPM - 40 psi

I have already replaced the oil pressure sender unit because the socket I bought for was machined wrong and I accidentally broke it trying to remove it.

The truck has 250,000 miles and I've been running 5W-30 or 10W-30. I bought it with 87,000 miles and have mostly changed the oil when the light comes on. I just hear a small ticking, but no knocking. Seems like bearings are loose from wear and tear and was thinking to switch to 10W-40 or thicker.

Back in February I did the intake manifold gasket and didn't change the oil right away. I covered the top of the engine with a plastic bag, but don't know if something got in there, or maybe it is just coincidence. I did see a residue on the oil plug the next time I changed the oil. Also, I have saved the oil filters since then, but have not opened them up.

Any advice is welcomed...

 

[df2x4]

I bought it with 87,000 miles and have mostly changed the oil when the light comes on.

What light are you referring to? Neither of my '97s have any kind of an oil light, at least to my knowledge.

 

[stutaeng]

Oh, sorry, it's a NBS (GMT 800.) Engine is the same though as GMT400.

 

[stutaeng]

I also noticed that the needle on the mechanical gauge does not jump or is bouncy; it is steady.

I switched to 20W-50 last night and got 10-14 psi at idle. No noticeable difference in engine sound or performance. I'll run this for a few weeks and we'll see what happens.

 

[Schurkey]

Low oil pressure is a sign of problems. That said, there's no telling how long the thing will go even with abnrormally-low pressure.

Hope for the best, prepare for a fresh engine.