I know its not an LT but I know you hooligans in here and someone might be able to help. I think my suburben 5.3 is toast.

I bought a 2000 suburban 4 weeks ago with 240k on it for $1800 from a guy who had just bought it when he crashed his wifes car and used it for 1000 miles until insurance came through. It had some strange grounding issue that caused random lights to come on some times like low washer fluid, low oil, ABS, BRAKE, and the oil pressure gage sometimes fluctuated, but it ran and sounded perfect. When I got it, it would have 20psi cold, and 40 warm, and on cold mornings when its parked with the nose slightly high in my driveway it would have 0psi for about 10 seconds and then it would come up, but it would have a little piston slap or knocking or ticking during this time so I did believe the gage, but then it would be 20 and all sounds would go away, and then 40 after about 5 minutes of driving and was fine. Sometimes the low oil light would be on even though it had a fresh 6 quarts, so I thought something was gummed up with sludge in the engine causing restricted flow. I had changed the oil after 300 miles even though the PO had changed it about 1000 miles ago when he got it. The filter came out heavier than Ive ever felt a filter, and was a Fram, and the oil was black. I put 5w30 Castrol synthetic blend in it again and the PO said he used 5w30 conventional. It was better, but after another 1000 miles the cold start oil pressure thing was getting worse again.

Last night I wanted to change the oil to see what the Castrol had gotten out, so I got it warm, got it up to 40psi, and then ran it hard from light to light up to 90 full throttle, 5500rpm shifts, trying to work some **** loose. After that, it was only 10psi for the last 2 miles home. I changed the oil, it was pretty dark, the filter felt normal, and it got some small clumps of sludge out. I started it, it took a few seconds to come off 0 oil pressure, went to like 15psi, and I said **** it and went to bed. I put 10w30 in this time thinking I wanted it to be a little thicker cold, but in hind sight, I think I should have gone with 0w30 since it seems like cold the oil wasnt moving enough.

Then this morning I started it, oil pressure came right up (I had it nose down in the driveway) it was 28 degrees out, and I went off to work. The oil pressure started coming down from 20 towards 10, and I got nervous and turned around. Then it kept falling, and eventually hit 0 and started ticking, and I was like **** it please make it home, and I kept driving it with 0psi for about 5 minutes, then as I got close to home it came back to 30psi and the ticking went away. Then I parked it, and froze my *** off in the Camaro to work. I think the 10w30 was too thick cold to move past the sludge blockages.

THE WEIRD THINGS I NEED HELP ON:
Why was oil pressure only 20 cold, and 40 warm? Thats the opposite of the camaro, which has 65 cold and 5-10 warm. Ive never seen a car be opposite like that.

Why would it take 10 seconds to build pressure cold? Why did it seem to matter when the nose was down vs up?

Why would the low oil light read on sometimes even with 6 quarts (6 quarts came out both times I changed it). Could sludge block this sensor?

My thought is that sludge was clogging either the pickup or the oil return passages in the motor, and that it needed the oil to warm up to move past the sludge blockages. I am going to pull the oil pan tonight and the valve covers and see what it looks like. My buddy has a 5.3 that was just used for dyno emissions testing at WVU with 2000 miles he can sell me for $600, or I found a low mile 5.3 locally with wiring, PCM, and coils for $650 that I might buy and keep the wiring, PCM, and coils for a PCM swap on the Camaro.

 

Check for actual pressure, sometimes my truck cluster acts up and is slow to show pressure on start up. Stepper motors on GMT800 are iffy in my experience.

Otherwise, check the oil pickup O ring and that the pickup is on tight. Could always shim the spring and port the pump too.

 

I'm interested in this too, my trucks been doin the same oil pressure thing for two years now, only in the winter. Funny thing is that it does it at the exact same intersection on my way to work everyday, it's on a slight incline also like you mentioned. I just pop it in neutral or brake torque it, and bring the rpms up to get pressure.... Verrrry strange

 

This will certainly get better exposure to LS experienced folks here in the genIII internal section.

 

The ticking and knocking tells me I really did have very low pressure, I was hoping to blame the stepper motor in the gage, but the ticking was telling me otherwise.

 

Have you cut open any of these filters? I'm curious why one filter was so heavy.

Any junk or glinting metallic stuff in the oil?

What filters are you using?

You should be using a 0W-x oil.

I'm thinking the pickup tube is blocked or the O-ring is cracked or not seated correctly.

 

Sounds like a clogged pickup tube or some junk has clogged up the pickup screen on the oil pump. Cut those filters open and see what's inside. You could also send your oil off for a small fee and have them examine it to figure out if any rod or cam bearings have given out, as well as other neat things.

 

I've got a new theory. There is sludge in the pan and when parked nose down it slides to the front away from the pickup so it gets oil pressure immediately. When it's parked nose up the sludge blocks the pickup. When I was romping on it yesterday it was sliding back, causing the low pressure. This could explain 80/TA/lt1s issue too as when cold on that hill it is sliding into the pickup. I'm going to stick a coat hanger in the oil plug hole and try to fish out some sludge before I pull the pan because that looks like an awful job.

 

Good thinking. Try one of those household tools used for unclogging sink/bath drains. It's got those grabbers on it to pull stuff out.

 

There is 10 miles on this oil in a paper towel cleaned oil pan.

 

1st poke

 

This is disgusting. CHANGE YOUR ******* OIL PEOPLE!

Poke poke poke, pour a little new oil in the top, flush. Repeat. No wonder my dipstick read over full with 6 quarts, there was a quart of sludge in there.

 

You'll never get all that **** out.

Replace the pan & pump.

A pan from GM comes with pickup tube, gasket, bolts & OLS. A nice (slightly) higher flow pump will do this old engine well as well as a timing chain.

 

This is what the inside of my engine looked like.

200,000 miles but relatively good running engine, no smoke, no noise, changed oil every 2,000 miles after 175,000 miles when I got it. Oil usually came out somewhat clean.

 

Pull the valve covers off. Im sure your going to find one or even both with peanut butter looking **** under it. The heads crack on those engines around the head bolt holes and let coolant into the oil.

Had this problem with my old tahoe, same problems as youve described and it was due to the coolant sludging up the oil and plugging up the filter. The bypass would open on cold startup and as oil warmed up pressure would raise as bypass closed.

 

I'm going to throw 5 quarts of $12 super tech 5w30 and a quart of marvel mystery oil in tonight and see what happens. If it still sucks I'll find a Craigslist 5.3 and cut thanksgiving with the family short and swap Friday and Saturday. It was still dripping crap out of the plug hole last night so I let it keep dripping all night, we'll see in about an hour.

Picture is from this morning before I went to work.

 

Mystery oil will make every gasket, seal and o ring leak. Ask me how I know I'd rather take the time and effort to pull the pan and replace that then deal with potentially changing most seals on the motor because if there is that much sludge in the motor, there will more than likely be some leaks that are plugged with sludge at the moment. Do at your own risk! Either way something has to be done though, just pick your poison.

 

X2.

PLUS anything made to loosen sludge puts the lifters and their tiny oil passages at the risk of getting clogged with debris.

Unless this motor is making noises or smoking, I'd rather fix up the oil system than take a chance on another junkyard pull that may be even worse.

New pan, tube, pump & chain = piece of mind and reliability.

 

Oh and I forgot to mention, Don't drop your Shiny iphone in that oil

 

Alright. I gotta give credit to the 5.3.

So I put 5 quarts of $12 super tech 5w30 and 1 quart marvel mystery oil in. Fired it up, instantly 45psi of oil pressure! But it sounded like a collapsed lifter, big tick. Had it running just enough time to roll it down the ramps, get out and listen to which side it was coming from for 5 seconds, then reach in and verify pressure and then kill it, still ticking loudly.

Cracked a beer. Stared at it. Finished beer. Started it. No tick! 45 psi! **** yea!

Let it idle 20 minutes and cleaned up a bit, told the wife I was going for a drive, if I'm not back in 10 minutes, just wait longer. Got about 8oz of pure sludge, like brownie batter out of it.

Drove for an hour and 40 miles, felt great, quiet, smooth.

Tomorrow I'll drive it 70 miles round trip to work then make the decision if I'm putting the wife, baby and dog in it to drive 3.5 hours tomorrow night.