Zachtaylor16

No there was no sludge and only about 1k miles on the oil and filter- both Mobil 1. What I suspect was that I had a failed oil filter. I also changed the pressure sensor and screen. I now get 35-40 psi cold idle and 30 psi warm idle. I get 45 psi highway cruising and 50 if accelerating. Hope this helps

Well all I wanted to give an update as the issue has been resolved. This will be a long post with a bunch of information so hopefully this can help someone down the road. Where I started. I was driving down the highway and my low oil light came on and the warning to shut off engine. So I pulled over and shut off my engine. I then checked the dipstick. My oil was on the low side of the checked boxes on the dipstick but still ok in range.My motor burns oil as most of these 5.3’s with afm does and if my oil is low I’ll get a low level indication. So I went ahead and added oil to the full line on the dipstick. I started my truck and it would go to 25 psi then slowly fall till the warning light would come back in. I’d shut it off and then it would come back on. Ok so I got the truck back to my place and knew the oil sending unit and thescreen below it are a common issue so I stopped into my local store and picked those two parts up and replaced. That had no affect. As I listened to the motor run there was no noise. No valve train noise, nor rod nock. Nothing. So I was pretty sure my engine was good internally. So then I wondered if it was the o ring on the pickup tube where it meets the oil pump. So to test this theory I parked my truck on a hill facing downward and I put in 2 quarts of atf and 6 oz of seafoam. I used these because they would still raise the level but also have high detergent content and can aid in cleaning. When I did this there was still no change. Still would start and go to 25 psi and then slowly fall. Now while doing these tests if I would press on the gas the pressure would go up. Not a lot but some. This indicated to me that my oil pump was good and not a problem I needed to look into first. So fast forward to today and I decided to do an engine oil flush. So I took out the 8 quarts of oil/atf/seafoam and first I look over it for metal shavings to see if there was any internal wear. Luckily the oil was in very good condition as it had only had 1000 miles on it. Then I took off the filter. I put on a napa oil filter, just the basic pro grade, and put in 5 quarts of napa oil, 1 quart of napa oil flush, and 8 oz of seafoam. I ran this through my truck for 30 minutes mostly at idle/low load with some acceleration mixed in. During this 30 minutes I was never below 30 psi of pressure. So I then removed the oil flush and put in 6 quarts of Mobil 1 and a Napa gold wix filter. I put another 45 minutes on the truck and 20 miles and had roughy 40 psi the entire time. So as of now it seems as the issue is fixed. Now where I was going after this (To help someone who this might not solve there issue) Next I would have put a manual pressure gauge onto the engine and verified that it was reading the same as the gauge. Now if it was reading good pressure but the gauge wasn’t three things could be the issue. 1. The oil pressure sensor is bad (make sure to use an oem AC delco part for this. And dorman makes a good screen to go below it) 2. The wiring for the sensor is bad. Or the stepper motor in the gauge cluster is bad. If the manual gauge matches what you were seeing on the dash gauge then my next step would be to pull the pan. If you are inclined and can do it yourself I highly recommend it. From here I would replace the pressure relief in the pan, the o-ring on the pickup tube into the oil pump and the pan gasket. Now before you pull the pan off I would also pull the windage tray off and manually inspect the bearing. This is whyI recommend doing this yourself. It’s a pain if you have 4x4 due to the front differential but you can verify the issue. Also check the pickup tube screen and make sure it’s not to dirty. Now put it back together add oil and start. At this point the issue should be fixed or you should have seen signs of bearing damage causing the low oil pressure. In that case it’s time for a rebuild or crate motor. Hopefully this can help someone in the future and please reply back to this post if you have questions.

I use atf and seafoam. I still need to dig some more on mine but I believe I have a much bigger issue and it may be time for a rebuild.

Pulling the oil pan off on the trucks is kind of a pain. Have to take the transmission brace off and lower the front diff usually to get enough room. I’d say maybe 2 hours of shop time.

Yes I have changed the sensor but still have no pressure. For me though when I do a cold start I get about 40 psi and then as the oil warms up and thins out I get to about 25 and it just slowly falls now. I added an extra 2 quarts of oil and about 8 oz of seafoam. And had my truck on an angle. I had no luck with this. Next will be oil change and to manual test pressure. I can’t hear anything coming from the motor but worried I’m having blow by somewhere. Also the oil pump seems to be working because as I accelerate the oil pressure goes up.

It’s recommended by a lot of people and some YouTube videos on it. Seems like 2 quarts will get enough to submerge the gasket without getting it on the crank. You also put your vehicle at a angle to help focus the oil where the pickup tube meets the oil pump. It’s not a long term fix however just a test to see.

I don’t have a manual gauge available. My plan today is to add oil to submerge the oil pickup tube gasket and see what information I can get. Then I’ll pressure test Monday just to have more information before I do anything.

Hello all I have a 2007 GMC Sierra new body style 5.3 with AFM (arghhh) and I was driving down the high way last night and I got a low oil pressure turn off engine warning an a P0521 code. So this morning I swapped the oil sensor and put in a new filter screen under the sensor knowing this is a common issue in these engines. That was no fix. The truck has about 215000 miles on it now and was wondering if I should try and chase on oil pump/other issues. I hear no noises and sounds like I have pressure but also worried that a bearing could be going out. I’ve had a cylinder 7 misfire code come up like 4 times over the last 2 years but it always goes away after about 5 minutes. It has a rough idle and I believe the cylinder 7 lifter is on its way out but no lifter tick. I was quoted from a new shop for a jasper reman engine but have heard the horror stories. I’ve just moved and don’t currently have a place to pull it apart and let it sit right now. Also when I had the issue I noticed that If I’d pull over and turn the truck off when I turned it back on it would go to about 30 psi then slowly drop. Normally I’d be over 40 psi at 65 mph. There are no leaks, oil is at the correct height and only has about 1000 miles on it. Any advice or experience would be awesome! Thanks in advance!!