10 psi when warm

[JohnnyA]

I have a 03 denali with a lq4 LS 6.0 vortec engine that has 180,000 and low oil pressure 20 lbs on cold start at sending unit and no nocks or ticks anywhere. I put two machanical gauges one at the outlet port of the oil pump outlet on the block and on a oil cooler bypass plate and the oil sending unit on the rear of the block that gives me oil psi readings. I use 5w30. I have low oil pressure when the engine is warmed. The machanical gauge on the outlet port of oil pump reads 8-10 lbs which is 3-5 lbs more than the other two gauges which read the same. I will be removing the bypass plate and replacing the oil cooler lines. I have replaced the pick up tube (PUT) twice. Originally there was a green PUT replaced with black one saw your video did job again with reddish orange oring. Cleaned oil pan and flushed engine with the first PUT change. The oil pan looked go with minimal film not even sludge. Next I put in a new milling m295 pump, no change in psi. Bypassing the cooler gave me 2-3 lbs more and I even tried 5w40 with bestline additive gave me 2-3 lbs more. I didn't plastigauge the bearings when I removed the pan, nor did I replace the timing chain, and didn't look at the front thrust cam plate. Bad move on my part. The only thing I can think of is internal bearing walking or increased bearing tolerances. So perhaps rebuild short block or buy a short block or both. Any insight would be deeply appreciated. Short block? longblock?? Where to buy? Or any other possible direction to look at or try? Also if I'm going to remove the engine I will want to beef up or refresh the transmission m32 4l65e or if you know of a better alternative I do tow a trailer. Once again I respect for time, knowledge, and insight. Keep up the good work on your platforms the really help the broke diy guys. Thanks JohnnyA

 

[Jimmyy]

I can't help you with 1st hand knowledge. Reading on this forum it important to prime the new pump. Others will chime in with more experience than I. Good luck.

 

[JohnnyA]

Thanks oil pump was primed still didn't change anything except eliminate a variable in a horrible oil pressure rubik's cube

 

[rockola1971]

This one is going to be a fun one to troubleshoot. No valvetrain noise at all? 10PSI on a warm engine, is that at idle? Whats the pressure cruising at 55mph? You do have some options depending on your answers before you go tearing engine apart or replacing it. Tranny ever been rebuilt in case engine has to come out or is tranny all original?

 

[swathdiver]

The old girl is tired and needs new bearings. Motor comes out for new camshaft bearings.

 

[SnowDrifter]

Does the pressure change with RPM? Could you pose some correlative numbers and pressures? Don't rev too high with that pressure please

 

[JohnnyA]

Thanks everyone! I removed the machanical gauge post filter and replumb the oil cooler lines. Cold start mid 35 at machanical gauge and 20 at sending unit. However, when warm the machanical gauge post oil pump is 20 psi and sending unit is 6-8. Presure looks barely adequate 1psi per 100 rpm up to 2700 rpm then it is below 1-100. Lq4 and m32 are original and untouched. 1700 rpm = 35 at machanical gauge 20 psi at sending unit. Looked through transmission for a look see and no oil on fly wheel. I felt some residue underneath and unknown if it's from a engine wash job that I did. Also knock sensor bank 2 came on unknown if it's from me washing the engine down essentially at the sending unit. I tell you now luck. Is it possible to refresh trany with corvette servo or what is best for towing. My trailer is 6000lbs and hauls very nice. I am in no hurry when towing. 60-65 mph thank you everyone .

 

[JohnnyA]

There is no valve train noise. Some noise just started almost sounds like timing chain tensioner.

 

[rockola1971]

With 180k on the engine and tranny, If it were me with your oil pressure problem and towing requirements I would have the tranny rebuilt for towing. Its already well past what id expect it to live at 180k and used often for towing. Then engine sure sounds like you have a bearing(s) leaking bad. You can verify this by sending in a oil sample to have it analyzed for verification. I would do that and then when it comes back as full of bearing material then you will have to decide between rebuilding your engine or buying a reman long block or new crate engine. Its your wallet so you will have to decide which works for you. Me personally I would buy the reman with a warranty unless the crate motor wasnt much more and get that warranty. I likely would not have local machine shop rebuild my engine because of time constraints and likely sucky warranty and cost is likely to be too close or exceeding a reman engine. If money and time is no issue then I would likely buy a performance/bigger CI's kit and bore my 6.0L and get a tune when its all back together. With towing often I would likely even put on a supercharger.

 

[SnowDrifter]

Confirming here:
You get 20psi hot at the pump. And 6-8psi at the sending unit? Both read by mechanical gauges?