Oil Gauge or Oil Pump or Gremlins?

[Roamingdoc]

Thanks for any thoughts. We have (My wife's Tblzr, drive to work, shopping, etc) an '02 Trailblazer LTZ, 4.2 L, 4W, with about 300K on it... very clean, runs superbly and the engine has never given us an issue. I have run Amsoil 5W-30 Signature Series Synthetic oil since day one... very careful and logged maintenance.
Yesterday we were in Flagstaff, cold (high elevation) and had parked. It was a 90 mile highway drive (70-80mph speed limit). We came out and started the car, I noted that the "oil pressure" gauge was not registering BUT there was no aberrant engine noise, nothing out of sorts, sounded normal and fine. I also noted the 'message' on the console, "oil pressure low". I gave the engine a single throttle blip and the gauge immediately registered 42-43.. and the message disappeared. I considered the 'no change in engine noise' and the fact that the gauge was registering normally and drove it 5 miles, no issue. So we came home that 90 miles and I stopped once (eat) and started, no issue. WE HAD immediately checked the oil levels at the first indication of this problem, normal read. We checked the oil level again, cold, a few hours later, absolutely normal. We started the car this AM, gauge registered 42 immediately. So I am sort of not looking at the 'pump' but not ruling it out.
I want to get a 'real' Oil Pressure gauge, any suggestions are greatly appreciated. Also, where is the sending unit for the oil reading?
And I will want to replace it, any suggestions on where to obtain and then any 'video' showing how? (I will have my mechanic install the "real" oil pump gauge. Thank you so much for any help.

 

[Mooseman]

The FAQ is your friend. Many discussions about the fake OP gauge and installing a real one.

Trailblazer oil pressure gauge doesn't tell you the oil pressure (4.2L engines) (YouTube)

So it's basically just a dummy light. Likely your oil pressure switch (not a sensor) is bad. Once you replace it, your issue should go away. If your connector is full of oil, it's a good indication it has failed. Clean it with brake or contact cleaner.

If you want to have a clear conscience, you can install a real one.

Where to connect a real pressure gauge

 

[TJBaker57]

want to get a 'real' Oil Pressure gauge, any suggestions are greatly appreciated. Also, where is the sending unit for the oil reading?

I do not call these "sending units" as to me this suggests it is more than just an on_off switch.

In the 4.2 six cylinder LL8 engine there is only the oil pressure switch, an on_off device incapable of sensing any other pressure differential.

The dashboard gauge reading is entirely a calculated value without relation to the true measured oil pressure.

I also own a 2002 and there is a known issue with a seal on the oil pickup tube inside the oil pan that gets old and loses the ability to seal. When this happens the oil pump can sort of "lose its prime", sucking in air and losing output pressure. This becomes apparent mostly in two conditions, one when idling with the engine hot like after a drive of no less than a half hour. The second opportunity to see the effects of this is at cold startup, like when it has been sitting overnight at temperatures below 25° F or similar.

I have opted not to replace this seal (O ring) as it is a costly affair.

I installed an aftermarket mechanical gauge so I can keep a better eye on things.

 

[Roamingdoc]

Thank you so much. I presumed that the so called gauge was an 'idiot light' more or less. While this YouTube video can be a bit profane the points are well made (

) as he runs the motor for a few seconds and still gets a reading. Additionally he has two other videos (part 1 and 2 not showing) - As noted the thread pitch on the output connection above the oil filter is a 2.0 and not as common... I am definitely looking at a new real gauge but seeing some of the input indicates maybe more trouble than its worth... ??

TJBaker, which aftermarket did you select?

 

[TJBaker57]

TJBaker, which aftermarket did you select?

I went basic, old school, and cheap, much like myself!! Mechanical gauge, nylon tube and such.





Somewhere here a member did a writeup of a very nice electronic gauge he installed that gave not only oil pressure but temperature as well.

 

[Roamingdoc]

Thank you so much... So you simply ran (if that is possible) the tube over and under and thru
the firewall (is that front left dashboard?) and the gauge is just resting? I ordered the 'sending unit' and a good socket to pull it, replace it... be safe.

 

[TJBaker57]

simply ran (if that is possible) the tube over and under and thru
the firewall

There is a whole lot of options and detail in this thread here. Pay particular attention to the talk of varying thread pitches as standard gauge adapters won't fit.

Oil Pressure Gage

Has anyone permanently installed a real oil pressure gage in the I6? I'm thinking of welding on a steel tee to to the old pressure switch with fittings for the switch and sensor. Is there an easier way?

gmtnation.com

I ran my nylon tubing from the front port near the oil filter then up the dipstick tube and across the top secured to the A/C line, along harnesses past the battery then back towards the rear and rather than drilling the firewall I passed through with the existing harness wiring. Well ziptied all along the way.

Once inside I ran up to the location seen in my picture of the gauge. One thing I did not like was the nylon tubing that came with the gauge was too short to reach so I added more with a compression coupling which must leak just a little as it gets oily, but not enough to drip any. I have bought a long length to replace the pieces with bit have not done that yet.

 

[Roamingdoc]

Got it... will read the link (sorry for the delay, got my Ford all serviced yesterday, why does it
hurt more to get under as we get older, hahah)... so about to beging the TBlzer. And "since" that first
moment up in Flagstaff, AZ it has NOT DONE IT once, drop the Oil Pressure. I am going to replace the sending unit. And not sure what code it might have thrown but will see if it did. Again, great help here always... thanks very much... Come to Prescott, AZ and I'll buy the beer.

 

[TJBaker57]

why does it
hurt more to get under as we get older,

I get under easy enough,,, it is the getting back up that is becoming an issue!!

 

[Roamingdoc]

Oh, agreed. My wife drags me up by me... well, anyway... Wink!

 

[ironring]

A question about the o-ring. Does anyone have any info on the part itself? Material, size, etc? I have a 2002 envoy with the 4.2L. I've taken the pan off (never wanna do that again) but getting the actual o-ring is proving difficult...

 

[Mooseman]

RockAuto has it, GM part # 12557752. Comes in a pack of 5. It's in closeout so may not be available for long there.

More Information for GM GENUINE 12557752

However, it should be available individually from a local dealer or through online GM parts:

12557752 - GENERAL MOTORS Oil. Seal. Engine. Tube. Gasket. Pump Pickup | Jim Tubman Chevrolet Canada, Ottawa Ontario

Genuine GENERAL MOTORS Part # 12557752 - Oil. Seal. Engine. Tube. Gasket. Pump Pickup. Strainer. Suction pipe. Ships from Jim Tubman Chevrolet Canada, Ottawa Ontario

parts.tubmanchev.com

 

[ironring]

RockAuto has it, GM part # 12557752. Comes in a pack of 5. It's in closeout so may not be available for long there.

More Information for GM GENUINE 12557752

However, it should be available individually from a local dealer or through online GM parts:

12557752 - GENERAL MOTORS Oil. Seal. Engine. Tube. Gasket. Pump Pickup | Jim Tubman Chevrolet Canada, Ottawa Ontario

Genuine GENERAL MOTORS Part # 12557752 - Oil. Seal. Engine. Tube. Gasket. Pump Pickup. Strainer. Suction pipe. Ships from Jim Tubman Chevrolet Canada, Ottawa Ontario

parts.tubmanchev.com

Much appreciated! I've been using the set of steps that I believe you put together for the oil pan removal, and they have been phenomenally helpful. One note re my 2002 Envoy: when I dropped the steering rack, I had to unbolt the power steering lines from the inside of the left front fender to give enough slack to get the rack low enough.