5.3l low oil pressure, please help

#1
Ok so I have a 05 chevy tahoe with the 5.3l in it. It has 197k miles and overall runs real good. I bought this truck about a year ago and it had 165k on it at that time and my oil pressure was about 10psi at idle and about 35-40psi on the highway. About 4 months ago it started dropping to 3-5psi at idle and 20-30psi on the highway. Well the 3-5psi was quite concerning. Every time I'd come to a stop at a light or stop sign it'd drop down and the warning bell would start going off. As soon as I started moving again the pressure would go back up and the bell would stop. Needless to say this was very frustrating. I started using heavier oil on my oil changes thinking it would help it and it would keep it from dropping below 5psi for about 2 weeks but would then thin out just enough and the bell would start going off again at every stop. I've watched alot of videos on this issue on the 5.3l and alot of ppl are saying it' the o-rng at the top of the oil pump pick up tube going bad and also alot of ppl say that it's a clogged screen in the tiny filter under the oil pressure sensor. 4 days ago I finally had the time to tear into it and try to fix this problem b4 I do real damage so I changed the o-rng and I put in a new oil pump for good measure and it did NOT change my oil pressure at all. Also I did check my pressure with a mechanical gauge and 3-5psi is accurate. Also there is no tiny screen filter under my oil pressure sensor. According to a ton of videos these 5.3's are supposed to have that filter. So idk if someone removed mine b4 I bought the truck. Regardless I still have bad oil pressure and myself and a few of my friends that are real mechanics are at a loss and are not sure how to fix this problem. Note- there is no engine noise, no knocking, valve chatter, etc. If u didn' look at the gauge at idle or hear the warning bell going off you'd never think anything was wrong. ANY advice would be greatly appreciated. Thanks in advance.
 

Mounce

Silver Supporter
#2
Your truck shouldn't have the screen as it's pre-afm/dod like my 03, I also didn't have the screen.

O-ring is a known possibility though but usually aerates the oil and causes ticking.
 
#3
There's also known issue with pressure regulator but would be at 0. You'll likely need a new new pump along with the O-ring.

Could also be a bad sensor. Try that first.
 

NJTB

Well-Known Member
#4
Do you know the service history of it, and are there any noises more than the usual? Sometimes with an engine with that many miles the crank/connecting rod bearings will wear to the point the oil will 'leak' from the sides causing a drop in pressure without the telltale knocks. Only way to check it is drop the pan and remove the caps.
The thicker oil should have improved it, maybe try a can of STP.
 
OP
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Bigtime101

New Member
#7
There's also known issue with pressure regulator but would be at 0. You'll likely need a new new pump along with the O-ring.

Could also be a bad sensor. Try that first.
The sensor is accurate, checked the engine with a mechanical gauge and it's reading the same as the sensor. And I just did the o-ring and oil pump. Nothing has helped it sofar. I didn't realize there's a pressure regulator on it. Where would that be located at?
 
OP
OP
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Bigtime101

New Member
#8
Do you know the service history of it, and are there any noises more than the usual? Sometimes with an engine with that many miles the crank/connecting rod bearings will wear to the point the oil will 'leak' from the sides causing a drop in pressure without the telltale knocks. Only way to check it is drop the pan and remove the caps.
The thicker oil should have improved it, maybe try a can of STP.
The engine doesn't make any noises. The engine sounds so good that my mechanic is puzzled. He said that if it were a lower end problem that the engine wouldn't run this strong and with absolutely no noises.
 
#9
It's within the pump body, the cylindrical part of it. Maybe a high volume and pressure pump might have helped. This video explains it and how to replace the pump without dropping the pan.


Another possibility is that the pickup screen is clogged. What you could try is drain the oil and clean it out by pouring some engine flush down the tube after removing the pump followed by some high pressure air.

For the pickup tube, I'd use this instead of trying to move the hold down that's welded on the tube.
https://www.amazon.com/Improved-Rac...83778&sr=8-1&keywords=Improved+Racing+EGM-500

Or use a bolt and washers like I did:
https://gmtnation.com/forums/threads/collapsed-lifter.16702/#post-528338
 
OP
OP
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Bigtime101

New Member
#10
It's within the pump body, the cylindrical part of it. Maybe a high volume and pressure pump might have helped. This video explains it and how to replace the pump without dropping the pan.


Another possibility is that the pickup screen is clogged. What you could try is drain the oil and clean it out by pouring some engine flush down the tube after removing the pump followed by some high pressure air.

For the pickup tube, I'd use this instead of trying to move the hold down that's welded on the tube.
https://www.amazon.com/Improved-Rac...83778&sr=8-1&keywords=Improved+Racing+EGM-500

Or use a bolt and washers like I did:
https://gmtnation.com/forums/threads/collapsed-lifter.16702/#post-528338
Thanks for the information. I've had the pan off and out and the whole front of the engine undressed to do the pump. While apart I cleaned the pick-up tube (inside and out), screen and replaced the o-ring. The pump was also replaced at this time. So unless the pressure regulator in the new pump is faulty I'm not sure where to go from here. I'm at the point where I'm seriously thinking about pulling the engine out and getting a used one with half the miles on it. I'm just trying to see if there's anything else that I can do that isn't gonna cost me a small fortune that might correct the problem. Thanks for your input, I'm just at a loss with this thing.
 
#11
It's quite possible that the engine is worn down to the point where clearances are too loose now that it can't buid up enough pressure. Maybe a high pressure high volume pump might help but might just delay the inevitable.
 

northcreek

Well-Known Member
#12
While you had the pan off it would have been a good time to plastigauge a few rod caps and mains, just to know if you were :deadhorse:
 
#13
You could also try Lucas Oil additive. It's thick like caramel and helps mine bring the pressure up to avoid a P0521.
 

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