Help understanding the 5.3

[TheEnder53]

So the engine in my Tahoe is a 01 LM7.

When i bought it, oil pressure was around 35-37psi warmed up. Then it was around 50-55 cold.

Oil presssure then began to drop when it was hot over the course of about 2 weeks. Lowest it got was 26psi hot.

Replaced the oil with 5W-30, oil pressure went back to how it was before.

There were also some metal spirals in the oil with some very small metal chunks. I am equating this mainly to the fact the drain bolt was severely stripped and the past owner replaced it with a 28mm aftermarket stripped oil pan bolt.

Engine runs absolutely flawlessly aside from what i think is some lifter tap/piston slap at a cold idle. It is so silent you can easily miss it though.

What happened for oil pressure to drop?

 

[strutaeng]

Sounds like you just bought the vehicle? You probably don't know what oil weight was in it before, so maybe that's why the pressure difference?

Are you checking oil pressure with a mechanical guage? The cluster gauge is not too accurate.

But 25 psi-ish is not bad at all. I wouldn't be concerned about it. Especially since it seems like it runs and sounds good.

It's normal for oil pressure to drop as engine gets to operating temperature.

 

[Marky Dissod]

Engine runs absolutely flawlessly, aside from what i think is some lifter tap / piston slap at cold idle.

0W30 may reduce cold engine noise, especially in winter.

 

[TheEnder53]

Sounds like you just bought the vehicle? You probably don't know what oil weight was in it before, so maybe that's why the pressure difference?

Are you checking oil pressure with a mechanical guage? The cluster gauge is not too accurate.

But 25 psi-ish is not bad at all. I wouldn't be concerned about it. Especially since it seems like it runs and sounds good.

It's normal for oil pressure to drop as engine gets to operating temperature.

Haven’t ran a mechanical gauge yet. I just picked it up in January and im still trying to understand it better lol.

I’m happy 25PSI is okay. I assume as long as its not reading 0 it should be ok.

 

[nonickatall]

Known problems with these engines are the O-ring on the oil pump, where the oil pipe that goes into the sump attaches.

These rings break down over time and then the oil pump sucks in air.

It always makes sense to replace this o-ring if you don't know whether it has already been done.

The oil pan must be removed to do this. Once you have the oil pan off, you should also replace the bypass valve on the oil filter. But otherwise I agree with the previous speakers, 21 PSI at idle with warm oil is okay and it is also normal for the oil pressure to drop when the oil gets warm. Mine is at about 50 psi when idling, after a cold start and drops to just over 20 psi in idle when the engine is warm.

 

[RST Dana]

Might want to have an oil analysis done. Some of your descriptions make me cringe about the future if things are up above the oil pan are not copacetic.

 

[cjmcglaughlin]

My 05 idles around 30 hot, maybe around 28-30 if a really long drive. I’ve been putting off doing the O-Ring, but I suspect it’s either that or maybe the guage itself. Or it could just be wear, idk, I have 164k.

 

[Doubeleive]

that would be scary (to me), every nbs I ever owned pretty much sat on 40 psi, except my 00 with a rebuilt engine that baby sat right about 70 psi 24/7
if you found metal in the oil pan (regardless of where it might have come from) then it might have got either sucked up in the pump or even the whole motor.
I would have a analysis done by blackstone, cross your fingers and go from there.
you might want to drop the pan and check that pump to see if there is metal stuck in it.
just speculation, it wasn't until I bought my 12 and saw the oil fluctuation 20~40 was a thing (now) but never on any of my nbs, I mean it might have varied slightly but not much

 

[OR VietVet]

So the engine in my Tahoe is a 01 LM7.

When i bought it, oil pressure was around 35-37psi warmed up. Then it was around 50-55 cold.

Oil presssure then began to drop when it was hot over the course of about 2 weeks. Lowest it got was 26psi hot.

Replaced the oil with 5W-30, oil pressure went back to how it was before.

There were also some metal spirals in the oil with some very small metal chunks. I am equating this mainly to the fact the drain bolt was severely stripped and the past owner replaced it with a 28mm aftermarket stripped oil pan bolt.

Engine runs absolutely flawlessly aside from what i think is some lifter tap/piston slap at a cold idle. It is so silent you can easily miss it though.

What happened for oil pressure to drop?

Mileage? Metal spirals? How small were the metal chunks? Pics? Had the previous owner just replaced the pan bolt?

My 162k miles 05 Idles at 50 psi cold and just below 40 psi warm. Climbs easily with acceleration. I have done the oil sump o-ring a while back, while pan was off. I just don't like the metal you found. Analysis is a must.

 

[cjmcglaughlin]

This is somewhat unrelated but how much driving does it take for oil to warm up completely for all of you? For example if I drive for only 20 mins or so my hot idle is closer to 33, but after maybe 30-40 mins of driving it’s closer to 30.

 

[TheEnder53]

Might want to have an oil analysis done. Some of your descriptions make me cringe about the future if things are up above the oil pan are not copacetic.

That is the goal once im able to keep oil IN the engine, lol.

I have to drop the oil pan and replace that gasket along with some other gaskets around the engine. Right now, it leaks around 1-2 quarts every 200miles.

Once im able to get the pan down, im replacing the sump o-ring, and i will check everything more when i look.

 

[TheEnder53]

Mileage? Metal spirals? How small were the metal chunks? Pics? Had the previous owner just replaced the pan bolt?

My 162k miles 05 Idles at 50 psi cold and just below 40 psi warm. Climbs easily with acceleration. I have done the oil sump o-ring a while back, while pan was off. I just don't like the metal you found. Analysis is a must.

They replaced the pan bolt with an oversized stripped plug repair bolt. It’s now around 26-28MM, and the spirals in the drain pan matched the size of the threads. That is what i thought it was. I think i have a picture somewhere.

As she stands right now, cold idle is around 45-50PSI and warm idle is around 35-38PSI. Gauge is a little hard to read and is rather get a mechanical pressure gauge on it and see for sure.

 

[TheEnder53]

This is somewhat unrelated but how much driving does it take for oil to warm up completely for all of you? For example if I drive for only 20 mins or so my hot idle is closer to 33, but after maybe 30-40 mins of driving it’s closer to 30.

Mine is fully warmed up within 20-30 minutes of driving.

 

[TheEnder53]

Here’s one of the metal spirals. The other stuff in the pan is (some) of the metal that was in it. The bigger chunks is outside debris. Along with hot oil pressure.

 

[TheEnder53]

Here is a video of her idling.

 

[Doubeleive]

This is somewhat unrelated but how much driving does it take for oil to warm up completely for all of you? For example if I drive for only 20 mins or so my hot idle is closer to 33, but after maybe 30-40 mins of driving it’s closer to 30.

just whatever it takes to get the oil up to about 180, I could probably do it in a few blocks if I really tried. a decent scanner should show you the oil temp

 

[Doubeleive]

Here is a video of her idling.

sounds ok anyway

 

[nonickatall]

This is somewhat unrelated but how much driving does it take for oil to warm up completely for all of you? For example if I drive for only 20 mins or so my hot idle is closer to 33, but after maybe 30-40 mins of driving it’s closer to 30.

Depends on a lot of circumstances. On a hot day it's faster warm, than in the winter. If you directly drive on the highway it's different than if you have stop and go in a big city.

But when the coolant is on temperature, your oil is warm too. Not on maximum temperature, but warm enough to have the viscosity it has.

 

[cjmcglaughlin]

just whatever it takes to get the oil up to about 180, I could probably do it in a few blocks if I really tried. a decent scanner should show you the oil temp

Depends on a lot of circumstances. On a hot day it's faster warm, than in the winter. If you directly drive on the highway it's different than if you have stop and go in a big city.

But when the coolant is on temperature, your oil is warm too. Not on maximum temperature, but warm enough to have the viscosity it has.

Appreciate the thoughts on this. I wonder if there’s any reason mine would go down a bit more on longer drives? Stepper motor?

 

[nonickatall]

Appreciate the thoughts on this. I wonder if there’s any reason mine would go down a bit more on longer drives? Stepper motor?

You need to understand how oil pressure in an engine is created.

The oil pump, which is driven by the engine and is speed-dependent, generates oil flow, not oil pressure.

This flow of oil is forced through the filter and transported through the oil channels to the bearings. This becomes oil pressure, because at the end of the oil channels in an engine there are usually plain bearings, for example on the camshaft and crankshaft.

The oil is pressed into these plain bearings and can only escape again with difficulty.

This nozzle effect creates back pressure and thus oil pressure.

Now there are several factors that ensure that the oil pressure is no longer the same as with a new engine.

Firstly, if your bearings in the engine are already very worn out, they can no longer hold back the oil, so the oil pressure drops.

As the oil becomes more liquid when it is hot, the oil pressure drops.

When the revolution is low in idle, the pump does not deliver as much flow, so the oil pressure drops.

If you drive for a long time, the oil is of course really hot and everything is really flushed through, so your oil pressure drops to its lowest value when idling then.

But as long as your oil light doesn't come on when idling and the engine has an oil pressure that is close to the middle (40psi) of the instrument display under normal load, everything is fine.