killernoodle

So I got my car running after Doug Herbert Racing did the rebuild on my LS6. They did rods, pistons, bearings, cam bearings, and assembled the shortblock.

I installed a melling high volume oil pump and installed the pickup and pan all according to the instructions (I'm very **** about stuff when engine building).

When the oil is at 90F, I'm seeing a 50psi oil pressure on idle (750-800 rpm), verified with another gauge. It also increases with rpms as expected. When the oil gets to about 200F, the oil pressure drops to about 10psi at idle and only goes up to about 40psi through the rev range. So far it's not making any noises when it's idling with such little pressure, but I don't want to damage the motor. I'm pulling the motor this weekend, is there anything I should check for with those specific symptoms?

01ssreda4

iTrader: (96)

Does it need thicker oil due to looser clearances?

03Sssnake

iTrader: (20)

oil pump relief valve/bypass hanging open? When the oil is cold/thicker it would not be as noticeable, but once hot and the oil is thinned, it shows up. Out of curiosity, what oil filter did you use? You may start there, cut it open and see if you have a lot of trash/metal in it. Then on to that oil pump, check/and or replace the spring and o-ring as well.

Old Geezer

iTrader: (3)

What does the build sheet show for brg clearances?
Are these pressures taken using a mechanical ga?

CHEVELLEPOSSE

I ring on pickup tube

CHEVELLEPOSSE

Sorry meant to say o ring

RockinWs6

YThats way too low, something is missing out of place or moved. Check oil gallery plug in the front and back and the cam bearings for walk.

99z28383

iTrader: (1)

I had a lifter fail on me and right when it started tapping really loud, I had the same symptoms as you. After getting everything together, I noticed the previous owner had pinched the pickup tube o-ring. Got it back together and when it's fully warmed up it never goes below 40 psi.

killernoodle

What's the easiest way to diagnose this? I really doubt melling would ship a pump with this problem, but I guess anything is possible. If I take the cap and spring out, will I see the piston wedged in there?

Pressures were taken with a new oil pressure sender (first thing I tried) and a PLX fluid pressure gauge. Both read the same thing, the PLX reads a couple pounds higher since it is plumbed in at the oil cooler bypass by the filter instead of at the top of the block.

I'm taking the trans out today for a rebuild and getting both ends of the motor opened up. I'll check the oil galleys, the pump, the o ring, and the pickup tube to pan clearance.

03Sssnake

iTrader: (20)

I used the same melling (10296) and had no issues, but I did take mine apart to clean/lube before installation, afterall...it is a mass produced part and I wanted to make sure there were no burrs/debris.

I still would check the oil filter first, start there before taking anything apart, cut it open and see whats in filter media. You may just try changing oil filter top off and see if problem persist.

if you decide to take the OP apart, here is a good thread..

Do not re-use the oil pump O-ring

killernoodle

Ok I finally got around to taking the motor apart. So far I've taken off the pickup and the o ring seems to be in good shape. When I put the pickup on the pump with the o ring it makes a pop and when I take it off it makes a pop. The o ring is definitely snug and in place. I took apart the pump and the pressure relief valve slides in and out nicely. The barbell in the back was installed correctly and the o ring looks good. The galley plug on the front of the motor also looks good. There isn't any debris in the pickup screen, nothing interesting in the pan, and the motor looks sparkling clean inside.

I'm going to take the valve covers off next. Should there be anything I should check for in there? I'm pretty much out of ideas.

RockinWs6

Check the cam bearings for walk clearance. Check the other bearings for clearance. Got to go through the wghole thing till you find something that makes sense.

killernoodle

That's my fear.

After looking at the pump, the outlet on it had a tiny ridge on it. It was almost like someone stuck something in the outlet and pried it up slightly. I don't think it was the cause because the block had an indentation in the same spot. I'm thinking the imperfection in the iron pump housing probably made the indent when it was tightened down and it still sealed. I filed it down anyways.

I'm still going to pull the cam and look at everything else. It just sucks it wasn't something glaringly obvious!

killernoodle

The cam bearings are all in place, and the oiling holes all line up. None of them were spun. The bearing surfaces looked good, as did the cam itself. So that leaves the main bearings to check, but honestly what are the odds that it's the main bearings and it hasn't blown up yet after a few hundred miles? It hasn't made any weird noises yet either.

Quick Ranger

iTrader: (2)

As stated before, what are your bearing clearances on the build spec sheet? What oil are you running? If clearances are looser, you will need a thicker oil.

killernoodle

When I took it to the machine shop, I gave them std size bearings. I don't think he did a line hone, and if he did, it was just a cleanup hone. The crank wasn't polished either IIRC.

I'm running 15w40 Rotella T. As stated before, the car makes great oil pressure cold, and it drops very rapidly when hot. 50psi @ 90F to 10psi @ 200F is a pretty big swing.

I guess I could take the main caps off and plastigauge them, but I somewhat doubt that's going to tell me anything worthwhile.

camaroboy408

iTrader: (6)

Why such a thick oil?

killernoodle

Because of the low oil pressure, duh

It was the first thing I tried to fix the issue. Low hanging fruit.