Jason MK

Hi everyone, this is my first post on LS1Tech! I love all the courtesy and helpfulness i've seen and have been browsing this forum for months. I finally have a question of my own.

About 2 years ago we purchased 2000 1/2 ton Silverado with a 5.3 Vortec. Soon after, we noticed at very low idle (in gear idling) the oil pressure would hit 0. We tried a new oil pump but that didn't help. It soon got to the point that even idling when warmed up it would reach 0 oil pressure. We checked it out with a mechanical gauge, too. We could not figure it out. We ended up buying a junkyard 5.3 for $300 and dropping it in there, and it's still running great.

It is about 1 and 1/2 years later and i want to take it apart and fix the oil pressure loss. I'm planning on dropping it into and older vehicle (fuel injection intact of course!) I was just curious if there was a common problem that caused these motors to lose oil pressure and some things i should look for. Oh yeah, it might be a 4.8 since it was in a work truck, how can i tell? Thank you everyone!

badazz81z28

iTrader: (6)

Spun bearings or excessively worn.

Jason MK

So it could be rod bearings, main bearings, or cam bearings? it does have 140k on it.

1FastBrick

iTrader: (16)

The difference between the 4.8/5.3 can be identified from the pistons. If the piston is flat it's a 4.8L if you can see or feel a dish its a 5.3L. You can attempt to check through the spark plug hole.

If the motor is out of the truck you can pull the pan off and look at the crank casting number. The block itself should have a 4.8/5.3 cast into the front and rear of it.

12553482 is a 4.8 crank
12552216 is a 5.3 crank

The 12552216 casting was used in various engines including the 5.3, 5.7, and 6.0 engines.

Jason MK

Thank you very much 1FastBrick.

1FastBrick

iTrader: (16)

It could be several things.

There is plug in the back of the engine with an O-ring if that becomes dislodged or worn it can bleed off pressure.

If the cam bearings spin it can also block the flow of oil.

If the o-ring at the pick up is not correct or gets pinched it could also cause a loss of pressure.

Not enough oil or wrong type of filter can also cause oil pressure issues.

Jason MK

I really appreciate the help. Is the plug you speak of behind the rear main seal cover? I will definitely look at all of the possibilities when i tear it down.

1FastBrick

iTrader: (16)

Yes, Its plastic and is referred to as a barbell. It diverts the oil through the filter in the illustration I have shown above.

barbell looks like this...

Jason MK

Finally got time and tried to pull the cam and the 3rd cam bearing was flopping around, keeping it in. I think i have found the culprit! Thank you all very much.