I've read for hours and still haven't seen anything solid. So, here we go.

Purchased a used 2011 LS3 with no background info other than it had roughly 30k miles.
Purchased used as a short block. I did NOT disassemble the bottom end as everything felt tight and everything I saw indicated a very low mileage motor as it was advertised.
Cam bearings looked excellent.
Installed a new Melling 10296. Heavy spring installed. Did NOT shim with feeler gauges upon install. Did NOT pinch O-ring. Engine on stand, assembly lube used. Not even a remote chance of it being the O-ring.
New valley cover. New pickup tube. SacCity barbell installed. Everything assembled correctly.
New oil pressure sensor. Checked 2 for verification. Two dash clusters that read identical. Have NOT ran manual pressure gauge. Two sensors, two clusters agree to the pound.
Johnson 2116LSR lifters.

20-50 Mobil 1.
50 degree oil:
Pressure at start up 800 RPM idle: 50 psi.
Pressure at 2000 RPM: 62 psi.
Pressure at 3000 RPM: 70 psi.
Pressure at 4000 RPM: Buries the gauge at 80 psi.

195 degree oil:
Pressure at 800 RPM idle: 17 psi
Pressure at 2000 RPM: 30 psi
Pressure at 3000 RPM: 35 psi
Pressure at 4000 RPM: 43 psi and tops out at about 45 psi.

No noises from the motor at any RPM range.
I know the GM specs and these numbers fall in there but in past experiences with several LS1's and Melling 10296 pumps these numbers are WAY off. My Vette with a 10296 and 125k on the clock still cold start idles, around 50 degrees, around 68 psi, hot idles at 46 psi and 2000 RPM on the highway at about 63 psi.

I just had Precision Pumps port and polish a 10365HV for this thing and it's ready to install but if I tear the front apart and swap it out and see similar numbers I'm not going to be happy.

Please, all comments are welcome but those with LS3 experience step up to the front.

Thanks.

 

Make sure he relief piston is not sticking. I know, new pump, but it happens.

 

That is definitely a possibility and the only one that makes sense to me at this point. Hoping for some other ideas and experiences.

 

Bump.

 

Yep..10296 pump here on the LSX427 and my oil pressure is 60-65 cold and 50 on a hot idle with 5W30. Why the 20W50 on a stock engine with stock clearances? Did you check rod and main bearing clearance? There's many things that cause low oil pressure and here's some of them.

Excessive bearing clearances.
Defective oil pump or pump relief valve not functioning properly.
Oil leaking past the barbell, cam retainer plate or valley cover.
Restriction in oil flow due to a clogged screen, pickup tube or an insufficient clearance from the pick up tube to the bottom of the oil pan.
Vectoring due to not enough oil in the pan and air being sucked in causing oil pressure fluctuations.

 

IS IT THE RIGHT O-RING ON THE PICK UP TUBE? couple of different colors

 

If on an Fbody pickup tube it would be the black one.

 

There's kind of a rule of thumb on pickup O-rings-
The fat one goes on tubes WITH a groove rolled around it where the O-ring goes.
The thin one goes on the tube WITHOUT a groove, AKA a straight-sided tube.

 

All good points. Started with 5-30. Hot idle was down to 15 psi. Put the 20-50 in to help it out.
I did not check bearing clearances.
COULD be the pump relief piston. This is where I'm leaning at this point.
New, carefully inserted SacCity barbell. New cam retainer plate, valley cover.
New pickup screen for the pan.
I don't see a lift problem especially at idle. Again, all good points.
Correct, green, o-ring is installed.