Chevy LS engine loses oil pressure

I saw an ad for a cheap LS motor. I'm assuming an LM7 and the ad states that "it loses pressure after a while". Another assumption on my part is that the seller is talking about water pressure, as he goes on to focus on putting on a new water pump. Do LS engines have any common issues with water pressure or pumps? Could this be a simple fix and provide a motor for my Challenge build? 

Ad here.   

Edit: Thread title is obviously wrong.

At that price I'd grab it and figure out the problem later. 

Buy it for $70 without the water pump and i’ll give you one for 20.  $90 5.3?  Do it now

then pull pan and pickup tube and inspect pickup to oil pump o ring.  It’s really the only “wear item” in the oil system because they get brittle and whatnot.  Also don’t discount E36 M3ty factory gauge being the cause of his problem.

High mileage wear will cause that also.

Is it a 5.3 with displacement on demand?  There is a fine screen under the oil sender, which is in the same oil gallery as the DOD actuation.  Neglect the oil changes, it plugs, oil pressure sender sees no oil pressure.

No matter the engine size, it will be due to neglect, I would imagine.  Well maintained things seldom lose oil pressure.

In reply to Streetwiseguy :

It's from a 2000 model year truck, so it's not DOD.

I just read a bit more carefully.  Yes, probably coolant loss.  The only expensive problem there is porous heads, or head gasket.  Certain heads would leak right around where the rockers bolt down.  Can be seen with the valve covers off, pressure testing, but with the engine out, thats not really practical.  That failure makes the engine oil brown, since you are adding coolant directly to the oil pan.  $125 is practically free, anyway.  Challenge car, add some cooling system sealant, and change the oil regularly.

It’s in your van now, right?

I saw this just yesterday and was thinking it was a shame I had nothing to put it in. 

Buy it!

It is possible for the oil pressure relief valve to be acting up. I had to replace my oil pump on a 25k miles ls3 because of that. Not common but it's usually an all or nothing kind of fail.

Read the article. The engine is most likely hurt.  If he is monitoring on the dash gage and a pressure issue is showing there it is not good. Those gages are not linear to the pressure. It would be good for parts etc.  

175k is right around the time when that oil pickup O-ring turns into an air pickup O-ring.  Air does not build good oil pressure.

Too old to be a DOD engine, which is known to eat the cam bearings and lose oil pressure that way.

Knurled. said:

175k is right around the time when that oil pickup O-ring turns into an air pickup O-ring.  Air does not build good oil pressure.

 

Too old to be a DOD engine, which is known to eat the cam bearings and lose oil pressure that way.

I've never actually seen the pickup tupe ring or the cam bearings fail on a 5.3L. Most oil pressure issues that I've seen have either been oil pumps or the AFM pressure relief valve on the DoD motors.

Knurled. said:

175k is right around the time when that oil pickup O-ring turns into an air pickup O-ring.  Air does not build good oil pressure.

 

Too old to be a DOD engine, which is known to eat the cam bearings and lose oil pressure that way.

 

 

Not to thread jack, but since we're on the topic, would that oring be the most likely cause for my oil pressure gauge to rapidly bounce between 20 and 40 at idle? By rapidly bounce I mean so fast that it almost looks like a blur. It smooths out at a steady 40 psi as soon as the engine gets a couple hundred rpm above idle, so I didn't think it was a gauge/sender problem. If it is the oring, how big of a job is it to change? Is the engine going to have to come out? 2002 silverado 2500hd 4x4 6.0. Thanks

Doubt that would be the o-ring, plus oil pressure couldn't vary that fast while running. Since it is bouncing fast, it probably is an electrical issue. I would try the sender first, easiest to change.

oil pressure decreasing as it warms is normal. 

 question is how much.

Old school says worn main bearings are usual cause.    Unless sudden.

Bouncing gauge is bad cluster.  The needles don't even react that fast to normal changes.

I have replaced scads of those O rings.  Most of them in vans, it seems vans get the oil hotter than pickups.  Oil pressure will come up from 20psi to 60psi just from that repair.  Usually the oil pan gasket is drooling at the oil passages at this point too, so it has to come apart anyway.

classicJackets said:

I saw this just yesterday and was thinking "berkeley yeah, five-point-three-eighteen-tee-eye!!!". 

 

FTFY

Knurled. said:

Bouncing gauge is bad cluster. 

Also, those gauge clusters were notorious for failing. 

iceracer said:

oil pressure decreasing as it warms is normal. 

 question is how much.

Old school says worn main bearings are usual cause.    Unless sudden.

This was my thought as well.  Ties in with the cooling system issues he was having.

In reply to bigeyedfish :

How does worn mains tie in to cooling issues?

In reply to DeadSkunk :

Produces more heat?

Sending unit and gauge clusters on these were also an issue.

DeadSkunk said:

In reply to bigeyedfish :

How does worn mains tie in to cooling issues?

I should have just quoted the first half.  Oil thinning as it gets hot leads to oil pressure loss.  If there is a cooling system problem, it makes sense that the oil would be getting too hot and thinning to the point that oil pressure drops.

Main reason manufacturers stopped putting gauges in cars.