Oil pressure drops after warm up on 2007 5.3L Suburban, 128k

Coconino84103 · March 30, 2019

Oil pressure perfect until a few minutes after engine warms to 210 then drops from 55+ to 20 psi while cruising and then to under 5 psi at idle. I have replaced oil sending unit. No improvement. Then dropped the pan and replaced O-ring, screen and pressure relief valve. No improvement. Then replaced oil pump with high velocity pump and did increase oil pressure from 40 to 55+ psi but then engine warms to 210 and get the same pressure drop. Then went back in and replaced the camshaft thruster plate. No improvement. Last ditch attempt, changed back to conventional oil and put a nice KnN oil filter. No improvement!!! This engine runs so smooth, cannot figure out what’s going on Help!

Dnt · March 30, 2019

Did you replace the oil sending unit filter screen when you replaced the oil sending unit?

swathdiver · March 30, 2019

3 hours ago, Coconino84103 said:

Oil pressure perfect until a few minutes after engine warms to 210 then drops from 55+ to 20 psi while cruising and then to under 5 psi at idle. I have replaced oil sending unit. No improvement. Then dropped the pan and replaced O-ring, screen and pressure relief valve. No improvement. Then replaced oil pump with high velocity pump and did increase oil pressure from 40 to 55+ psi but then engine warms to 210 and get the same pressure drop. Then went back in and replaced the camshaft thruster plate. No improvement. Last ditch attempt, changed back to conventional oil and put a nice KnN oil filter. No improvement!!! This engine runs so smooth, cannot figure out what’s going on Help!

Could be bad cam bearings but first you should check that the AFM VLOM is not leaking. Remember the 4 posts in the "lifter valley"? Those eight holes can leak over time bleeding off precious oil pressure. Pull the intake and VLOM and have a look.

A quick way to check that the o-ring is not the problem is to overfill the motor with an additional 2 quarts of oil while idling, enough to submerge the o-ring.

SunShine01 · March 30, 2019

It just might be general wear and loosening up of bearing and crank etc.

If your engine isn’t rapping from lack of oil circulation I wouldn’t be so concerned. You just might need refreshing up your internals. High capacity pump should be circulating oil. If not, it’s obvious it’s “bleeding “ out from areas because of wear and loosening of tolerances.

It happens with aged engines, especially those engines that idle a ton. Idling is hard on an engine because of heat and low oil circulation kinda permits more wear with friction on internals.

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Brian715 · March 31, 2019

If it doesn't rattle the top end then it has enough pressure. I drove mine for over two years where it would drop to 0 at idle and never get above 25 or so. It would start to make noise about the time the red light would change to green and the noise went away after the rpms came back up. Never quit but finally had to change the worn out engine. 5 psi at idle that comes up right away with a little throttle is enough. If it didn't come up I would worry. Otherwise drive on.

Coconino84103 · March 31, 2019

Does anyone know what the gap clearance should be for the main and rod bearings using Plastigauge for this 5.3L engine

swathdiver · March 31, 2019

33 minutes ago, Coconino84103 said:

Does anyone know what the gap clearance should be for the main and rod bearings using Plastigauge for this 5.3L engine

LMG and LC9

Crank: .0008-.0025 inches

Rods: .0009-.003 inches

Coconino84103 · April 16, 2019

Have now replaced the main and rod bearings and problem still not resolved

swathdiver · April 18, 2019

Lifter valley posts and VLOM? Cam bearings?

Clrkknt · March 13, 2021

Short answer: acdelco oil filter 12706595

Now the rest of the story: this a $7 filter made for the corvette. I have a 2009 Silverado 5.3 with the dreaded afm. As soon as my truck would get up to temp the pressure would drop out to nothing. I changed out the oil pump, the o-ring, and the oil pressure sending unit (4 times). I finally called my awesome mechanic to see about an engine swap and he told me to try this first. I could not believe it, it totally works. Now my truck starts out at around 45 psi at start up and after it warms up it stays around 40 at 2000rpm and goes down to 20psi at idle. Can drive all day no problems. I don’t know the why or how but for $7 you have to give it a shot! And then spread the word!! Make sure to respond to this so others know it’s real and works.

swathdiver · March 16, 2021

On 3/12/2021 at 9:03 PM, Clrkknt said:

Short answer: acdelco oil filter 12706595

Now the rest of the story: this a $7 filter made for the corvette. I have a 2009 Silverado 5.3 with the dreaded afm. As soon as my truck would get up to temp the pressure would drop out to nothing. I changed out the oil pump, the o-ring, and the oil pressure sending unit (4 times). I finally called my awesome mechanic to see about an engine swap and he told me to try this first. I could not believe it, it totally works. Now my truck starts out at around 45 psi at start up and after it warms up it stays around 40 at 2000rpm and goes down to 20psi at idle. Can drive all day no problems. I don’t know the why or how but for $7 you have to give it a shot! And then spread the word!! Make sure to respond to this so others know it’s real and works.

PF64 right? Thought they had different threads but guess not since you're using it.

Clrkknt · March 16, 2021

Yes pf64. Threads are the same. All I'm saying is for $7 it is worth a shot.

Tj9012 · July 15, 2021

I’m having the same problem and have changed everything even change to the oil filter like every one says to still 5 psi on oil pressure at idle I don’t know what else to do it’s go’s to 40 psi when I start it and when it gets warm idle at 5 psi and about 15 to 18 when driving

Johnnyblazed · August 22, 2021

Im having similar issue on 2007 envoy.denali 5.3l. I installed a new mellings high volume pump, with the higher pressure spring as well. Cold it runs beautiful, NEVER any noise regardless of pressure. I checked.pressure with mechanical gauge to.confirm my cluster wasnt bad as i was told the clusters do go bad as well and could generate a false condition so it is important to hook up a mechanical gauge, dont trust the dash gauge, or scanners due to the fact some.may read data from the dash. My performance engine guy and gm tech are suggesting worn cam bearings, while another guy i work with who does.all the engine rebuilding (im a transmission specialist) is suggesting to replace valley plate expeccialy due tonthe fact it is leaking from the rear side. If the gasket is to worn he said it may be leaking to much internally at the seals, at idle 0, stayed 0 while moving prior to oil pump upgrade but now it will increase once rpms are up until it gets even hotter before then it stays at 0 with the rpm increase. If you have afm/dod it may be worth a shot. Another engine guy that does High Performance Engine also suggested a different melling's pump that could possibly patch the problem he said it runs about 75 PSI cold and I would probably still hold 20 to 30 hot but I really do not want to change the oil pump again as it is incredibly difficult while keeping the oil pan on I did it once already and I do not want to do it again the 4 x 4 version is very labor-intensive to drop the pan on my Envoy I am going to try a new Valley plate and see what happens