Oil pressure gauge

[Vicompc]

Yesterday I was driving about 70 mph and the oil pressure dropped to zero and the DIC indicated to stop the engine. I pulled off the highway and into a parking lot, as I was turning in the pressure came back up to normal. I checked the oil and it was about 1 1/2 quarts low, would this cause the gauge to drop to zero or could it be a flakey sending unit? BTW everything seems normal now. I checked for other posts indicating the same issue but they all point to the truck at idle and the pressure gauge going to zero.

 

[bobdec]

Oil guage on the 4.2 is a dummy reading generated by the PCM based on RPM and rides up ther near 40 lbs. The 4.2 has actually has an oil pressure switch that trips at something like below 8 lbs and it feeds the PCM. When the switch trips below that number the PCM drops the guage display to 0 .

My guess is a 1.5 qts down you sucked the oil pan sump dry, had a lot of oil up in the valve train not returning fast enough to fill the sump, dropped pressure below the switch level, the switch flipped and the PCM set the gauge to 0 lbs. Once oil returned to pan, pressure went above the 8 lbs gage goes back to 40 lbs..

This is one thing I did not know prior to purchasing mine, I thought, man this thing has 40 lbs at idle, that's great !!! Have not had problems, and would not have changed my purchasing opinion, but it sure would be nice to know actual oil pressure, it's a good indicator of how well an older engine was maintained. Rule of thumb for older GM engines is 10 lbs per 1K RPM, not sure how low/high these 4.2 run...

 

[Vicompc]

Thanks for the info, that makes me feel a little better. Now if I could figure out where the oil is going.

 

[CaptainXL]

Now if I could figure out where the oil is going.

What is the maintenance history with oil changes on the engine?

Are you using the correct viscosity 5W-30 oil and the recommended GM PF-61e filter? I would start there and then troubleshoot the oil pressure situation. According to a couple GM TSB's regarding oil pressure loss, several aftermarket oil filters do not work well or have the capacity to work well with the engine. In some instances using aftermarket filters can result in engine damage.

I would suggest you change the oil yourself and have the oil filter cut open and observe the filter media for sludge or chunks of stuff and possibly for collapsed media. If you can't or don't want to do this have a shop do it for you. It is possible the engine oil change interval was neglected and sludge has formed inside the engine.

 

[RayVoy]

The oil pressure sensor, on the I6, is a known failure. It failed on mine (an '05 Envoy) and produced the same problems you are having.

It's cheap (I think around $20) and easy to change (it's mounted just about the oil filter). I changed mine and never had the problem again.

Yes, it could have been due to the low oil, but if it happens again, it is probably the sensor.