40 to 20 oil pressure

[dlnelsonroca]

Hello! I've bought another car, but I didn't see on the site where to add it to my other car. The new bought car is a 2011 GMC Tahoe Denali Hybrid, with a 5.3 motor, 4.4, and 166,000 miles. I recently had to replace the lifters and have the valves ground, etc. Also put in a new oil pump and new o-ring on the oil pickup tube. The problem is that when the engine is cold it registers at 40 but when warmed up it goes to a little above 20, and stays there whether just getting out of auto idle or doing 65 mph.

The symptoms confuse me because the 20 plus is only when it warms up. Is this an oil viscosity issue or a crankshaft bearing issue or what? In my area there's no one with a good scanner or diagnostic tools except a Chevy dealership three hours away. With your knowledge base and experience your recommendations would be most welcome. Thanks!

 

[Mooseman]

I just went through the exact same issue with my Avalanche with the 6.0L and also had a similar issue with my Saab when I did the DOD delete. Who did the work? Was the correct oil pump used? Not familiar with the hybrid but does it have DOD/AFM as well?

With my Avy, I had a low pressure issue exactly like yours but, AFAIK, the oil pump is original. I did a flush, changed the oil and filter and it now it stays just under 40psi while cruising hot. Figure there was either blockage at the pickup or the bypass was stuck open.

With my Saab, after I did the DOD delete and replaced the oil pump, pressure was staying on the low side. So much so that it would throw a oil pressure sender performance code. Turned out that I used the wrong oil pump. I replaced it with the DOD version and pressure was back up. Didn't save it though as it eventually developed a rod knock.

If it uses a regular oil pump, I'd look at swapping it to a high volume/high pressure version or even one for DOD. It could just be wear that the pump can't keep up. I remember someone called the oil pressure gauge as the "how worn is my engine" gauge.

 

[dlnelsonroca]

Great! Thanks. I'll get some engine flush and give that a try before anything else. It will be a few days before I can get to an auto parts store, but I'll report how it went with the flush.

 

[Mike534x]

That's interesting, I noticed something similar with the vans we have at work. We've got a few 2015-2019 Chevy Express Vans with the 6.0 and when cold they're at 40+ PSi but when warm it hovers around 25-30. Cruising usually has the gauge registering at 40ish and doesn't really jump up unless you nail the gas.

When my parents had their 07 Tahoe, there was similar readings as well for the oil pressure. We just figured it was normal especially with the AFM set up, and when they traded it for a '13 Tahoe (what a lemon that thing was) did the same exact thing as well with only 40k miles. Yours has a 5.3? I always assumed the Hybrid models came standard with the 6.0.

What oil pump did you put in it? The factory OEM style, or one from like Melling?

 

[dlnelsonroca]

We used the factory OEM oil pump. After the an engine flush it seems to be doing better, although at times it dips a little lower than I like. But over the pressure's up some.

 

[Mooseman]

As an FYI, I replaced the oil pump in my Avalanche with a high volume and pressure unit and my pressures are much better now. Hot idle it sometimes still goes down to 20 psi but at anything above idle, it's at least 40 psi. When cold it is higher. It should be higher since the pump's bypass has a 60 psi spring.

I wonder if it might be the bypass in the oil pan which was originally for the DOD that's bleeding pressure although it's suppose to release at 75 psi to protect the DOD system.

 

[mrrsm]

There are two "Last Items" in the Food Chain that come into play here before the Oil Pressure is supposed to finally register as being "Real" on the Dashboard Oil Pressure Gauge: The Oil Pressure Sensor and the Oil Pressure Sensor Stainless Steel Filter-Screen.

The linked Video below shows why this was possibly overlooked as it is anything but an easy job to R&R even just to perform a visual inspection. Even in the absence of having a P051 Code getting thrown... the Oil Pressure might register quite low and still meet the lowest threshold of the factory limits before triggering any DTC.

Lucas Wollermann spent almost 30 minutes going through one painful step after another showing us Why and How this ridiculously complicated effort must be done (especially when performing an Engine Flush or Top Engine Cleaning with Sea Foam or ACDelco Top Engine Cleaner) to eliminate both of these items before deciding on the unlikely causes for such a persistent Low Oil Pressure being worn out Crankshaft and-or Connecting Rod Bearings:

You know... I'd Bet a Brace of Gutenberg Bibles that if someone created an "After-Market Three-Pin Wire Harness Extension" for that Rear Mounted Oil Pressure Sensor & S/S Screen and also made an "M16X1.5 Oil Port Adapter" to thread into the one so very accessible on the Lower Front Driver's Side of the 5.3L and 6.0L LS Engine Blocks to accept an "ACDelco Oil Pressure Sensor and Filter Combo Unit"... they could make a FORTUNE.

Having these optional items available qnd installed would remove all doubt about the condition of the Gerotor Oil Pump and the "Real Oil Pressure" by being able to easily Test or perform the R&R of that OP Sensor and Screen Combo in just a few minutes.

 

[Mooseman]

The filter is for protecting the AFM VLOM from debris that may have slipped by the primary oil filter. That's its only purpose. The sensor could be moved to an alternate port however, if that filter were to get clogged, there would be no indication of it and your AFM may not work properly without adequate oil pressure.