Intermittent low (e.g. zero) oil pressure issue - GM 6.0 V8

[W116_036]

2005 GMC Yukon XL Denali AWD with the 6.0L V8
Over 300k miles but oil changed regularly with Mobil 1, usually before the OBC recommends it.

The truck has started having an issue where oil pressure kind of meanders and then suddenly tanks to near zero at highway speed/constant load, and the dash says engine oil pressure low. Then as soon as that happens it shoots up to 40 PSI + and goes away for a while. And so the cycle repeats.

I just changed the oil with Mobil 1 5W-30 HM and FRAM extra guard filter 2 weeks ago. Tomorrow I am going to replace the filter again to rule that out (my thoughts being it perhaps has a restriction and goes to 0 PSI, then the bypass valve opens, hence the sudden increase in pressure - a shot in the dark frankly and worth $10 and 5 minutes of my time to replace).

We had a similar low oil pressure issue years ago (2-3+ years ago) that required replacing the oil pump. I did not do the work since I don't have the required lift at home, so I farmed it out to someone else. My fear is that it is needed again. Or that the oil pickup is somehow getting blocked. I THINK we used a Melling pump but do not recall for sure..

Obviously I checked the oil level and it's fine.

Any ideas? I am dreading having to remove the oil pan again to investigate considering what a PITA it is on this truck with the AWD front diff and so on. Considering the mileage, I might even think about driving it until it dies and then junk replace it with a used/junkyard engine with fewer miles... these engines were used in a lot of trucks right? So I shouldn't have an issue finding one for cheap?

Driving video illustrating the issue:

 

[c502cid]

Sounds more like a bad oil pressure sender to me, but that is at best an internet guess. When the pressure goes to low to zero, is the engine making any noise?

 

[tiger862]

The oring is problematic at the pickup tube for oil pump. Pan has to come off. Before I would do this I would run a manual gauge to verify the pressure drops. Most sensor problems seem to peg the gauge to full.

 

[W116_036]

Sounds more like a bad oil pressure sender to me, but that is at best an internet guess. When the pressure goes to low to zero, is the engine making any noise?

After doing more reading after posting this, looks like replacing the oil pressure sending unit is step 1. I am ordering a DORMAN 926040 replacement as we speak.

It has been making a lifter noise for the past year or so but it has not gotten any worse. As for what noise it makes when the oil pressure goes low, I have no idea. I am not the driver and also it happens at speed, so I doubt it would be perceptible anyways.

The oring is problematic at the pickup tube for oil pump. Pan has to come off. Before I would do this I would run a manual gauge to verify the pressure drops. Most sensor problems seem to peg the gauge to full.

Sensor fault pegging the gauge to full is not reassuring... I guess we'll see once I replace the sensor. I would hope that o-ring was replaced at the time the oil pump itself was, but can't say for sure.

 

[dogememe]

Dorman? Eek.

 

[Lubener]

If your engine actually had very low oil pressure, the engine would become very noisy and likely would have seized up by now.. Since you didn't mention that, I would suspect a faulty sending unit or wiring..

 

[bullwinkle]

Dorman? After all that money & work?? Get an OEM sender, the last thing you want is that thing cracking and spewing oil everywhere

 

[Snagglefoot]

I agree the pressure sensor should be changed, but you are due for a new O ring at the oil pump. I just did it on my 2008 6.0 on my Suburban. Search O ring and Snagglefoot and you’ll see my write up. My oil pressure jumps to 42 psi upon start up and cruises at a steady 40 psi. I had to drop the front diff about three inches. It’s not as scary as it sounds, but I did mine on a lift. I have 260,000 miles on mine. First the sensor, then if it acts up, the O ring. The 6.0 does not have the filter screen below the sensor so you can skip that step. Good luck.

 

[Snagglefoot]

Try a few You Tube videos on how to get at the sensor. Here’s a screen shot from a good one. It’s tight back there.

 

[atikovi]

I am ordering a DORMAN 926040 replacement as we speak.

If you're firing the parts canon, at least use oem parts, not junk like that. Ideally you would connect a manual gauge to rule out the sender, the gauge and the wiring because all three are suspect. And I use 5W50 on a 6.0 with 100K less miles.

 

[Astro14]

If you're firing the parts canon, at least use oem parts, not junk like that. Ideally you would connect a manual gauge to rule out the sender, the gauge and the wiring because all three are suspect. And I use 5W50 on a 6.0 with 100K less miles.

This.

 

[BrendanC]

second on using ONLY GM/delphi/denso electronics on a GM product. they will throw a fit.

 

[Bud_One]

If you're having lifter noise and the oil pressure drops while driving , it's the oil pump o-ring.
Same thing happened to our 6.0 LQ4 and oring fixed the issue.

 

[Cujet]

We had a similar low oil pressure issue years ago (2-3+ years ago) that required replacing the oil pump.

On this truck? If so, maybe the tech replaced the O-Ring and the issue is the sender.

I really prefer a mechanical oil pressure gauge when troubleshooting these issues. Certainly the sending unit can be bad, but so can other connections and grounds.

 

[Snagglefoot]

There is a way of connecting a mechanical gage without messing with the existing pressure gauge. Just above the oil filter is a boss that will either have a block for the engine cooler lines or else will have a factory block-off plate. If you remove what’s there you can mount a custom block-off plate and that has a 1/8” NPT port drilled and screw in a gage. Here are a couple plates. If it’s a four wheel drive you might need a 45 degree elbow to avoid the front drive shaft. You can source them through Amazon or your local speed shop. The last photo shows the factory plate in place, looking up from below. You can see it’s just above the oil filter. In an engine with oil cooler lines, that would be a block with two cooler lines attached.

 

[Fitz98]

I don't want to give any bad advice when it comes to oil pressure, so don't ignore the advice from the above members who have a lot more experience than I do in these matters, but didn't these vehicles have issues with the instrument cluster and gauges?
I saw in your video that your digital displays were going haywire intermittently.
Oil Pressure Gauge Faulty Stepper Motor Video

I like the idea of verifying real pressure with mechanical gauge to rule out electronics.
Here was a video I saw that shows some diagnostics for comparing a mechanical gauge reading with the cluster gauge. This turned out to be a bad o-ring.
Mechanical Gauge Reading - Bad O-Ring