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.