Soo on my recently re-required 05 GMC Sierra 5.3L I am having some oil issues.

The cold oil idle at first crank is 38psi.

After it gets somewhat warm 10-15 minutes in it will idle from 20lb to 40lb back and forth.

When the truck runs from 20 minutes it will idle at 40 and hit 60 on hard acceleration.

Now we replaced the oil pressure sending unit and there was oil inside the sensor plug in part the female and male end had oil covering them. I cleaned them best I could and put a new sending unit in. The pressure is reading a little bit better, but it is still bouncing from 20 to 40lbs at luke warm/warm idle.

Now the truck makes no noise what so ever. No lifter noise, knocks or anything.

We hooked up and snap on tool to it. The engine is idling at 550 which seems low...the oil pressure is reading is 16 to 24 warm by the pcm.

I'm thinking there maybe some oil resude on the connections.

What mechanical problems could be leading to this?

BTW the oil pressure stays 40 plus and does not fluctuate under load.

 

These truck stock should be at 500-550rpms ac off and 600ish rpms with ac on.

Gm states that the truck can have no less than 7 psi of oil.
Truck should be at 40-60 cold start, and idle at 35-40psi. At 2500 rpms it should be at 60psi. At 3k should b above 60.

These trucks has HUGE issues with the oil pick up tube seal. They get worn and hard and allow air to be sucked up into the pump instead of oil. Causing the oil to airrate itself. Could be a cause but considering a $1000 oil pump replacement or doing a $30 oil pan gasket, oil change and a $6.00 dollar O-Ring. Id do that first.

My truck had that issue and at 2500 rpms it was at 40 and i thought that was normal. After i did that o'ring i wad amazed on the pressure i picked up.

 

Pm me if you have any questions

 

the aerated oil still shows pressure so you cant go by that. when i had a bad oring the lifters were noisy and the oil pressure jumped around but never showed very much lower than normal.

 

The sensor only picks up oil. So if air is getting sucked up with oil it will only pick up the oil in the sensor and the volume of oil will be less. Ive seen trucks come in with 10 psi or less and not make noise and they dont seem to think its an issue.

 

Well i took your advice...from searches and what you said the oil pick up tube seal seems to be the culprit.

Today we started a tear down.

Oil pan leaking...check.

Rear main leaking...check

Rear cover leaking...check

Oring on pickup tube...super check! It was so brittle that when i tried to remove it it broke in half. I also could barely bend it and it would break.

I think i caught this just in time. I'll finish the truck either tomorrow or Monday. We just stopped for some family weekend activities. I'll report back once its back together.

Also if anyone is wondering on a 6" lifted truck you must pull the trans back to get the oil pan out...I pulled mine out anyways to do the rear main so. This motor has 221k...maybe I should have just swapped it...but it runs so great...I wanna see if I can make it hit 300k...also original trans too.

 

Sweet!! Im gald thay helped man! Jusy make sure yo add silicone on the oil pan gasket where the timing cover and rear main set against it and it should last! I got almost 300k on mine with the mods in mt sig.

 

Just wanna report back that indeed the oring was the problem

New rear main, new oil pan gasket new pick up tube oring.

No more leaks and oil pressure is holding 60 cold..40idle and 60+ on acceleration. For anyone with this issue do the oil pickup tube oring.

Maybe some people googling this problem will fine this post.