low oil pressure truck runs good

[davig]

When I first start up the truck everything is good and about 20-30 min into being hot the gauge starts to go down around 25 wile 45mph and at idle it goes to red and I het the ding " low oil pressure". I hooked a gauge up too it. It read about the same maby 5 more then the dash gauge. I replaced the sender but keep getting the same problem. I can't see or smell Amy diesel the oil ether. Any suggestions?

 

[MACKIN]

What is the oil presure at idle hot on the mechanical gauge? How many miles on the truck?

 

[gmc502]

low oil pressure when hot usually means a bearing clearance problem.I'd pull filter and cut it open and check for bearing material.

 

[davig]

Bearing from what? That don't sound good. It has almost 165000 and if the mechanical gauge was higher by 5 or so of whatever the das gauge was saying

 

[Brent@LDS]

Have you checked to make sure you don't have fuel in your oil?

 

[davig]

Yes and I didn't see or smell any

 

[davig]

So I just hooked up the mechanical again I am getting about a 10-13 pound difference between thr two gauges. The mechanical gauge is higher anf about where it should be.

 

[PACougar]

So I just hooked up the mechanical again I am getting about a 10-13 pound difference between thr two gauges. The mechanical gauge is higher anf about where it should be.

Sounds like it's time to get the stepper motors in your dash replaced.

 

[davig]

But if its the stepper motors. Why would I be getting the low oil pressure message? Does the "message board"( I don't kno what you call it). Go off of the needle gauge? Just trying to understand.

 

[PACougar]

But if its the stepper motors. Why would I be getting the low oil pressure message? Does the "message board"( I don't kno what you call it). Go off of the needle gauge? Just trying to understand.

Good point, clearly my reading skills are lacking tonight. Have you checked it with a scanner that can read the oil pressure PID?

 

[davig]

I just have a autocal and the mechanical. I dont think you can go in and read the oil fro the autocal can you? no other way to check it besides those.

 

[PACougar]

What was the actual reading from the mechanical gauge at idle at with the engine revved up?

 

[davig]

Idle hot was about 15 truck gauge was a hair from red red. and I dont exactly remember rev but If I remember right it was 40 at 2000rpm. And truck gauge wad about 30. I can get better numbers tomorrow.

 

[PACougar]

I believe 14 at idle when hot is what GM says so you clearly have a sensor/gauge problem. Perhaps a slight short or ground issue. I would check the wires from the sensor to the ECM.

 

[davig]

Ok thanks

 

[BHoward6.6]

Specifications Oil Pressure - Minimum- Hot - at idle 98 KPa 14 psi Oil Pressure - Minimum - 1800 RPM 294 KPa 42 psi Oil Relief Valve Opening Pressure 441 KPa 64 psi Piston Cooling Jet Valve Opening Pressure 196 KPa 29 psi

 

[BHoward6.6]

Engine Oil Pressure

 

[davig]

So it looks like its something with the computer then if the truck thinks it doesn't have pressure when it really does then? Where do I go from here?

 

[Burn Down]

Sounds like it needs a new pressure sensor...

 

[PACougar]

So it looks like its something with the computer then if the truck thinks it doesn't have pressure when it really does then? Where do I go from here?

I would test the sensor first. If it tests out good, I would then test the wiring from the sensor to the ECU. If that's good then you have a ECU problem. I wouldn't assume just because you replaced the sensor that it can't be the problem.