Skinny

iTrader: (11)

Fresh rebuilt 346. I installed a ported LS6 oil pump from Thunder Racing. I kept my tolerances within factory spec, but on the loose end of it. As such, I expected about 5psi lower pressure. Cold oil pressure isn't bad, but once HOT, the oil pressure is very low. At idle (~1000rpm) I see around 18-20psi. WOT, high rpm only goes as high as maybe 45psi. I hooked a mechanical guage up to it to see if the guage was reading off. I found that at about 35psi on the dashboard guage, the mechanical guage showed about 25psi. I only had a few ideas for what the problem was. Of course there's the infamous pickup tube o-ring being pinched, but the motor was on a stand when I put the pump in. I think it would be really hard to mess that up, but still a possibility. Another possibility is because of the Rollmaster timing chain, I had to space the oil pump out to clear it. I then had to bend the pickup tube a little to make it fit into the pump. Possibly the tube wasn't going into the pump squarely, causing a similar situation as the pinched o-ring. The only other thing I could think of was a faulty oil pump.

Last night I pulled the front cover off and inspected. The pickup tube looked to be square and the o-ring was not pinched, so I put my stock oil pump back on. I put it all back together and installed the mechanical guage. At cold start, the oil pressure was about 35psi (on the mechanical guage). I took it up to about 5500 rpm and hit about 80psi. After the car got hot, though, the pressure dropped to about the same as before. Now I'm about out of ideas. Can anyone help??

PappyDan

iTrader: (4)

on the front and the back of the block, is these white plugs that fit in the ends oil gallery.
these plugs are directional and can be put in wrong, most engine builders leave out the back plugs and only insert the plugs in the front of the block.
one of the plugs can be placed in backwards or one if not two of the plugs could have been left out.

had this show up on another thread, same problem, he had to pull the motor but he did find out that the back plug was left out, after he placed them in. bam 75 psi at idol, 85 at wot.

Skinny

iTrader: (11)

Thanks. I'll pull the front cover off tomorrow and take a look. I built the engine, but nothing about those plugs stands out in my mind. I don't specifically remember taking them out or putting them in, but I don't remember NOT messing with them either. I'll see what I can find.

Slowhawk

iTrader: (12)

If the plugs were out there would be NO oil pressure.Sounds like the clearances are loose somewhere causing the loss of oil pressure.Maybe a QTP high pressure/volume oil pump would help.