Low Oil Pressure Warning Light

[estone4009]

I have a 1999 5.3L Silverado with 77,000 miles. The engine has just went through a major repair job having the head gaskets replaced. It was leaking coolant inside the engine. All the puch rods were replaced in the process. The engine was cleaned the best as humanly possible. When the engine warms up to operating temp and I go to a complete stop then the oil pressure gauge drops to about the first mark. We thought the problem would correct itself because of the coolant in the oil last time. Any ideas on where I can hunt down the problem on this? I know the oil pressure is not very high at idle either way on these engines.

[desertmike1]

I have a 99 5.3 W/80,000 and my pressure is 40+ idling on a hot day, with 10/30 Valvoline!
The first mark on your gauge is 5psi, this is not good.
I would first trouble shoot the gauge and sender to validate the readings and work out from there.

Don't drive the truck until you get this resolved, or you "will" have bigger Problems.

-Mike

[estone4009]

Does anyone know where the oil pressure sending unit is located on the truck? And how would I go about troubleshooting the gauge? And where is the actual oil pump located on this truck?

Thanks

[jeverett]

From what I've been told, GM says that their engines only need 5psi to lubricate sufficently, I had my head gaskets replaced last year so I asked them tons of questions. My truck did this one time while I was on my way home from Bill Heard (before the gaskets), the pressure dropped, and the motor started knocking. I had no choice but to try to go home (45+ miles) and after a few minutes, it went away and never did it again. Now my pressure is 40+ idling and around 60+ normal driving.

[estone4009]

The problem is mine has been doing the low oil pressure thing for six months. After 1 week on the new head gaskets it still is doing the low oil pressure thing. Could my oil pump be bad? Does anyone know of any tips for trying to track this down?

Thanks

[jeverett]

Where did you get the work done? If the problem started after they installed the head gaskets, I'd make them trace it.

[estone4009]

This was happening before the head gaskets were replaced. We were hoping that the coolant from the head gasket leak was causing the oil pressure problem but since the coolant leak now appears fixed I'm not sure which direction to head. Either way I need to try and diagnose it myself. The head gaskets set me back too much for another shop visit.

Thanks

[jeverett]

Yeah, I feel your pain. Well, you know the oil pump has to be in the oil pan, I don't know how many ways there are to test them, but either drop the pan, or pull the engine to access it. It seems like it couldn't be much more than either the pump itself, or the pressure sensor, which I have no idea where that is. I do know there is a sensor in the side of the oil pan, but I don't know what it monitors. I'll do some looking and see what I can come up with b/c I'm curious myself.

[estone4009]

My pressure is about 30psi at normal speed and about 5 psi at idle with my foot on the brake. If I put the truck in park the pressure jumps bak up to about 15psi. I think with the transmission in drive it pulls the engine down and the pressure.

[desertmike1]

estone4009,
I need to apalogize for over-reacting you might be OK, but right on the cusp.
I did some reading in my shop manual and here are the MIN acceptable oil pressure/RPM tolerances.

1000 RPM 6psi
2000 RPM 18psi
4000 RPM 24psi

This has to be done with a (Mechanical) oil pressure gauge connected in parallel with your oil pressure sender, located at the rear L/H side of the engine. It is the only sensor on the back of the engine, mounted vertical

Your oil pump (unlike the old days) is now mounted dirrectly to the crankshaft behind the timing chain cover at the front of the engine, and it is now a rotor pump instead of the old style gear pump. There is a steal oil pick-up pipe flange mounted to the pump that drops down into the sump.

I can only think of 6 things that would give you low pressure indication,
(1) bad sensor or gauge.
(2) bad oil pump.
(3) loose oil pump pick-up tube.
(4) obstrucked oil screen.
(5) bad oil pump releif valve (if equiped).
(6) worn connecting rod, or crank main bearings.

You can buy an off the shelf after market mechanical oil pressure gauge from any auto parts store for relatively cheep, and this will atleast give some piece of mind as to where you might go next.

-Mike

[estone4009]

After looking through a shop manual it is clear that changing a oil pump requires a majority of the front of the engine be torn off. I'm not sure I could tackle that. I will try and find a mechanical gauge and see what my actual pressure is.

[flynfol]

a clogged oil pickup screen sounds probable. unless you had been driving for quite some time with contaminated oil which would have worn your bearings causing increased bearing clearance and consequent low oil pressure. the fact that it doesn't rise very much with rpm increase, sounds like a clogged pickup. try a heavier weight oil as an experiment. if pressure increases, than probably excessive bearing clearance, if it decreases, probably the pickup. good luck!

[estone4009]

If it is the oil pickup what is the best and cheapest way to go about cleaning it?