NEED HELP Oil Pressure guage drops to zero (sometimes) during idle

[stvrob]

2006 TB EXT 4.2L L6 288,000 mi
A few times, the indicated oil pressure on the dash gauge drops to zero when idling. No check engine light or any other warning is displayed. First occurrence appeared after I changed the alternator but don't see any connections I might have damaged or left unconnected.
I have briefly reviewed some of the threads and watched Mooseman's video about tapping the pressure gauge at the hex plug next to the oil filter to read the pressure directly. I havent done this (yet), and frankly I'd rather not.
But if the pressure really were dropping to zero, wouldn't it trip a check engine light immediately thru a separate circuit?
I am about to change the oil and filter, and was considering increasing the viscosity to 10W-40.
Is it worth dropping the oil pan to check to o ring at the top of the pick up tube? Is that a straight forward job?
Any other suggestions?

About 6 months ago I found all the intake manifold bolts to be loose, I tightened them all up and have had no problem with blowby gasses near the throttle body air plenum since.
Any ideas would be welcome.

 

[TJBaker57]

2006 TB EXT 4.2L L6 288,000 mi
A few times, the indicated oil pressure on the dash gauge drops to zero when idling. No check engine light or any other warning is displayed. First occurrence appeared after I changed the alternator but don't see any connections I might have damaged or left unconnected.
I have briefly reviewed some of the threads and watched Mooseman's video about tapping the pressure gauge at the hex plug next to the oil filter to read the pressure directly. I havent done this (yet), and frankly I'd rather not.
But if the pressure really were dropping to zero, wouldn't it trip a check engine light immediately thru a separate circuit?
I am about to change the oil and filter, and was considering increasing the viscosity to 10W-40.
Is it worth dropping the oil pan to check to o ring at the top of the pick up tube? Is that a straight forward job?
Any other suggestions?

About 6 months ago I found all the intake manifold bolts to be loose, I tightened them all up and have had no problem with blowby gasses near the throttle body air plenum since.
Any ideas would be welcome.

If it is a 4wd model dropping the pan is a MAJOR undertaking. Even on a 2wd model it is still a big job.

My best recommendation is to install an aftermarket true oil pressure gauge as the factory display is not a true gauge at all. If you have read a few threads about oil pressure on a 4.2 you must have come across this fact already.

There is only one way to learn what is truely happening here and that is to at the minimum test the actual oil pressure with a test gauge when the engine is HOT. It will be significantly lower when HOT vs when just "warmed up".

 

[stvrob]

If it is a 4wd model dropping the pan is a MAJOR undertaking. Even on a 2wd model it is still a big job.

My best recommendation is to install an aftermarket true oil pressure gauge as the factory display is not a true gauge at all. If you have read a few threads about oil pressure on a 4.2 you must have come across this fact already.

There is only one way to learn what is truely happening here and that is to at the minimum test the actual oil pressure with a test gauge when the engine is HOT. It will be significantly lower when HOT vs when just "warmed up".

Thanks,
I could rig up a true gauge. I was reluctant to do so because the drop to zero is so intermittent, and I'm guessing it would only happen in traffic when the engine is completely hot. I could conceivably run an HDPE tube through the firewall to a gauge strapped under the dash.

 

[mrrsm]

Performing @Mooseman's suggested hook up of an Analog Oil Pressure Gauge will ultimately answer the question, albeit with a bit of physical difficulty maneuvering things around, but result in the satisfaction of getting a definitive answer. THESE are the things that might have gone wrong:

(1) The Engine in question here has more Miles on it than" Hecksher's Pet Goat".

(2) High Mileage Engines all suffer from Mains and Connecting Rod and Thrust Bearing Wear.

(3) Loose Babbitt Bearings bleed out oil under pressure profusely from in between the bearing surfaces and the journals.

(4) A Worn Out Blue Viton (PTFE) "O" Ring can flatten out and leak in AIR since the idea here is to prevent the loss of suction between the Gerotor Oil Pump and the upper flange of the Oil Pick Up Tube, thus dropping Oil Pressure.

(5) The Screen End of the Oil Pick Up Tube eventually can become clogged with Flaked Off Carbon Chunks and Gas Gum cause by Excessive Piston Ring Blow By, thus reducing the volume of oil able to get vacuumed into the Gerotor Oil Pump.

(5) Switching to a Higher Viscosity Motor Oil may not improve things, since any increased suction might cause a catastrophic failure of the Blue Viton "O" Ring ...and will affect the performance of the Cam Phaser when Thicker Motor Oil is pumped in with difficulty getting past the CPAS Solenoid.

 

[Mooseman]

90% of the time, this is caused by a faulty oil pressure switch. Replace it. It is cheap and easy enough to just try that.

The other 9% of the time, the stepper motor for the pressure gauge in the cluster is faulty. Don't bother with it as the pressure displayed is fake. If it were truly low oil pressure, you would also get a "Low oil pressure, shut off engine!" message in the DIC or a "check gauges" light if an LS truck.

The last 1% is an actual pressure issue to be verified with a real analog pressure test gauge.

 

[TJBaker57]

Thanks,
I could rig up a true gauge. I was reluctant to do so because the drop to zero is so intermittent, and I'm guessing it would only happen in traffic when the engine is completely hot. I could conceivably run an HDPE tube through the firewall to a gauge strapped under the dash.

I did exactly that except I have my gauge up on the dash in the corner where I can see it without taking my eyes off the road.

My low pressure is the 1% Mooseman spoke of, an actual low pressure. Only occurs at idle when hot or on first start after sitting overnight and ambient temperatures below freezing.

In my case it is a leaking oil pickup tube seal. But with the gauge right there for me to monitor I am not overly concerned.

 

[GlensG8]

2006 TB EXT 4.2L L6 288,000 mi
A few times, the indicated oil pressure on the dash gauge drops to zero when idling. No check engine light or any other warning is displayed. First occurrence appeared after I changed the alternator but don't see any connections I might have damaged or left unconnected.
I have briefly reviewed some of the threads and watched Mooseman's video about tapping the pressure gauge at the hex plug next to the oil filter to read the pressure directly. I havent done this (yet), and frankly I'd rather not.
But if the pressure really were dropping to zero, wouldn't it trip a check engine light immediately thru a separate circuit?
I am about to change the oil and filter, and was considering increasing the viscosity to 10W-40.
Is it worth dropping the oil pan to check to o ring at the top of the pick up tube? Is that a straight forward job?
Any other suggestions?

About 6 months ago I found all the intake manifold bolts to be loose, I tightened them all up and have had no problem with blowby gasses near the throttle body air plenum since.
Any ideas would be welcome.

My experience showing zero oil pressure on our 2008 Trailblazer LS 4.2 online 6 S engine: We were driving & I heard a faint lifter noise like they were low on oil. It wasn't loud and there was no way I should be hearing that since I use very good oil & filter plus keep the oil changed. (I take good care of our cars.) I checked the oil & it showed full. We started to drive home & then I saw the oil pressure guage showed zero oil pressure! I immediately pulled over & shut the engine off. I tried to start it again & the pressure showed normal; (about 41 lbs.) but I drove for about a minute & the guage went to zero again. We were about 40 miles from home & I decided to have the car towed home.
I was wondering if the oil pump screen was getting plugged up with sludge since the guage would be OK then quickly drop to zero. I did wonder though that I wouldn't have sludge since I am vigilant at changing my oil plus I use either Mobil 1 or Royal Purple oil plus those filters? We had the Trailblazer towed to a "good" ? auto repair place & they told us we need a new/rebuilt engine because of the zero oil pressure issue!
Anyway, I decided to do the list below instead and it worked!! (Thank God for that!!) Our engine is purring very nicely and you can hardly even tell it is running!
Here is what I did & in this order:
- Do not start the car anymore now!
- Drain the old oil out & reinstall drain plug.
- Fill the oil pan with kerosene only
through the dipstick tube up to the full
line with a very small funnel. (Put rags
underneath to catch spills.) 7 quarts??
- I let the kerosene sit in the pan 24 hours
then drained it then repeated that step.
(Do not start the car with kerosene in it!)
- Put in the drain plug & fill with cheaper
oil & a new cheaper filter plus I put in a
bottle & a half of Liqui Moly Engine Flush
- Start the car & run it about 15 minutes
checking the oil pressure guage.
(My guage read & stayed normal now.)
- Drain the oil & try to get every drop out.
- Put in the drain plug.
- Fill up to the full line on the dipstick*
with a good 5W30 oil such as Mobil 1
and I also put in 1 qt. of Lucas oil
additive. (Do not over-fill past the line.)
- Put on a new Mobil 1 oil filter also.
- I now installed a new oil pressure sensor.
(I just tightened it tightly by hand.)
- The engine should still be warm.
- Start the car & keep an eye on the oil
pressure guage. Mine not only read
normal but it was even higher at about
46-47 lbs.
This saved our engine and at least $7,000.00! It will cost some to do this but it was worth it to us! (This cost us about $300.00.) I didn't think that our cars would have a sludge problem but even being vigilant this car did so I plan on doing this to all our cars. Good luck & keep your oil & filter changed. God Bless!
~ Glen in Michigan

 

[mrrsm]

Concur completely with @TJBaker57 ...

SunPro Analog Oil Pressure Gauge (Or one like it...) ...FTW.



The Moral of the Lost Oil Pressure Story may have a Happy Ending

-= IF =- ...

The Oil Blockage at Position (1) on the Diagram for the Oil Pick Up Tube Screen gets CLEAN enough to avoid any Accidental Strong Vacuum or Excessive Gerotor Pump Suction at the Blue Viton "O" Ring or Orange Gasket Seal at Position (2) ...causing that Seal to Fail:

 

[TJBaker57]

(My guage read & stayed normal now.)

I assume you mean the FAKE FACTORY OIL PRESSURE GAUGE IN THE DASH??

I notice that nowhere in the post does it acknowledge learning/ knowing that the number displayed in the factory oil pressure gauge of a 4.2 Vortec is a make beleive value generated by the PCM based not an actual sensor input but rather a calculated value based on engine rpm, temperature etc.. You can actually pull the wires off the oil pressure switch and the gauge will still display the same value !

 

[Mooseman]

Start the car & keep an eye on the oil
pressure guage. Mine not only read
normal but it was even higher at about
46-47 lbs.

@GlensG8 , you do not mention if you installed a REAL oil pressure gauge. If you are going by the one in the dash, IT'S FAKE. It cannot tell you the real pressure as it is fabricated by the PCM. In fact, if you unplug the the oil pressure sensor (actually a SWITCH), the PCM will continue to send fake pressure readings to the gauge. All it can tell you is if you have oil pressure or not, like an idiot light. If the pressure drops too low or is 0, the gauge will drop to 0 AND you will get a warning, either from the DIC or the dash warning light. I think you merely experienced a faulty oil pressure SWITCH, which is a common failure part. And since you replaced it at the same time as all the rinsing you did, there is no way to verify if it was the switch or the oiling system that was at fault.

Recommended method of diagnosing oil pressure warning issues (reading of 0 AND warning light/DIC message):

1. Replace the oil pressure switch to eliminate that as the source of possible false warnings
2. If still getting low pressure warnings, investigate further using a real pressure gauge
3. Go from the results of the real pressure readings

If only getting a 0 or erratic gauge reading with no message or warning light:

Diagnose as a faulty gauge stepper motor and verify oil pressure with a real pressure gauge. To verify the faulty gauge, unplug the pressure switch and observe same erratic or 0 pressure from gauge in cluster.

Edit: @TJBaker57 , we posted at the same time

 

[crimecanine]

I notice that nowhere in the post does it acknowledge learning/ knowing ...

@TJBaker57 and @Mooseman , what do you think of the lifter noise that @GlensG8 mentioned as a sign of (truly) low oil pressure?
(Clearly a real gauge would be preferred.)

 

[Mooseman]

It's possible there was a pressure loss or could have been just noticed when it was always there before but got that message and became more sensitive to it. Again, we may never know.