Oil pressure from 0 to 50 until engine warmed 06 Enovy 135k miles

[Robmoo]

When I left work yesterday I noticed that the oil pressure was a hair above zero. As the engine warmed up during my highway drive the pressure went up to 50 and then settled at the usual 40. When I got home I checked the oil and it was in the middle of the crosshatched area at the end of the dip cable. So it isn't a low oil issue.

What's up? I read 1 post on car gurus that it isn't unusual for our oil sender unit to go out. It is an 2006 Envoy with 135k miles.

 

[TollKeeper]

A bit more info is needed.. Do you have a V8 model, or a I6?

The 5.3 is known to have issues with this sensor, although I have never personally had issues with either of my V8's.

The 4.2 gauge is a fake reading, and I wonder if its not just a stepper motor on the gauge cluster.. Which is a known problem for ALL gm products 1999-2009. The reason I suggest this, the little display on the cluster would have said something if it was really that low.

 

[Mooseman]

Checked his profile and he has the 4.2 so that oil pressure reading is fake. It's likely a bad stepper motor if you're not getting any other messages or lights, especially if you have a DIC, it would give you a "Low oil pressure. stop engine" message.

 

[TJBaker57]

If one has Torque Pro this here will display what the PCM is telling the gauge to read in psi. At least it does so for my 2002 4.2 and my 2005 Yukon 5.3.

If your gauge is in kPa just leave off the 0.145038 kPa to psi conversion multiplier.

This could be used to check your stepper motor, the two should pretty much match up.

 

[mrrsm]

The only REAL Way to know what your Oil Pressure is from a Cold Start through to a Warmed Up Engine condition is to install a TRUE Analog Oil Pressure Gauge with a LONG enough Hose to allow the Gauge Head to rest nearest the Windshield and be able to observe the Rise and-or Fall Off of Oil Pressure during your Test Drives.

The Nominal Range of Oil Pressure for the GMT360 4.2L LL8 Engine is 12 PSI at Idle near 600 RPM and 65 PSI at around 3,000 RPM. An Excessively Dirty, Clogged Oil Filter can raise Oil Pressure at Idle and even allow the Gerotor Oil Pump By-Pass Valve to open wide and allow Un-Filtered Motor Oil to pass directly into the Oil Galleries.

After you Check Your Oil Level FIRST... "Follow The Bouncing Ball" of what follows to get this job done:

(1) Purchase THIS M16 X 1.5 to 1/4" NPT Oil Gallery Adapter Plug with Copper Sealing Washer:



(2) Purchase a DECENT Oil Pressure Gauge Kit with a LONG Hose that can reach from the Oil Filter Manifold up and over the Engine Block and allow the Gauge Head to rest adjacent the Windshield in Plain View:



(3) Remove the Hex (H-8) Plug from the Right Front Passenger Side of the Lower Engine Block:



(4) Install the Auto Meter Brass M16 X 1.5 to 1/4" Adapter... Do NOT Over-Tighten this Item:





(5) Thread in the 1/4" NPT Male Hose End and snug it up TIGHTLY to a Leak-Proof condition:



(6) Run that Black Hose upwards and then snake it over the engine block and out from under the Rear Hood to a position where you can observe it while taking Test Drives:

(7) Observe the Gauge BEFORE Starting the Engine:



(8) Observe the Analog Oil Pressure rise ( or fall off and become intermittent and unreliable) AFTER Starting the Engine and compare what you see with the Dashboard OPG at the same time to know precisely what the Engine Oil Pressure is on the Analog Gauge as the Motor Warms Up ...For The MOST Reliable Indications of Actual Oil Pressure:



(9) After these Test Drives(s) Reverse - Remove all of this Rig and carefully re-install the H-8 Oil Gallery Plug after touching up the Threads with a Non-Hardening Permatex Sealer. Then Re-Start the Engine and Check the area for any Oil Leaks.

(10) Large Fluctuations in Oil Pressure at any time; whether at idle or whenever observing Rising RPM, can indicate problems with a Worn, Torn or Failing Gerotor Oil Pump Rubber Grommet (Orange for later Model LL8 Motors ) or Blue Viton Rubber "O" Ring Type Seals on the 2002-2003 Model LL8 Motors in between the base of the Oil Pump Pick Up Tube and the Gerotor Oil Pump Manifold. A Clogged, Blocked Off and-or Occluded Oil Pick Up Tube Screen can be caused by an excessive build up of Gas-Gum Varnish and Carbon Build Up therein can also cause Oil Starvation and Air Cavitation at the Gerotor Oil Pump interface and create a catastrophic Oil Starvation condition .

Images Courtesy Amazon and @MAY03LT YouTube Video...

 

[Mooseman]

An Excessively Dirty, Clogged Oil Filter can raise Oil Pressure at Idle and even allow the Gerotor Oil Pump By-Pass Valve to open wide and allow Un-Filtered Motor Oil to pass directly into the Oil Galleries.

Just a small correction. A clogged oil filter will cause the oil filter bypass valve to open, letting unfiltered oil into the engine (dirty oil is better than no oil). This bypass valve is not in the filter but in the filter mount in the engine block.

The oil pump bypass will open if the oil pressure is in excess of its top oil pressure, somewhere above 65psi. This will come into play in the case of cold thick oil that is causing excessive pressure and will close again once pressure is back to normal. It does not bypass the filter. It can become stuck and allow the oil pressure to drop continuously however, this is a particular problem on some V8 engines. Haven't heard of these engines having this problem.

A particular problem it could have is a leaking pickup to pump seal but this affects mostly the older O-ring style. Your '06 should have the newer flat washer style. As suggested, you should confirm what your oil pressure is like. Before shelling out money for a gauge set, check if your local parts store rents them out for free.