Oil pressure perfect until a few minutes after engine warms to 210 then drops from 55+ to 20 psi while cruising and then to under 5 psi at idle. I have replaced oil sending unit. No improvement. Then dropped the pan and replaced O-ring, screen and pressure relief valve. No improvement. Then replaced oil pump with high velocity pump and did increase oil pressure from 40 to 55+ psi but then engine warms to 210 and get the same pressure drop. Then went back in and replaced the camshaft thruster plate. No improvement. Last ditch attempt, changed back to conventional oil and put a nice KnN oil filter. No improvement!!! This engine runs so smooth, cannot figure out what’s going on Help!

 

Engine has 128k

 

Sub’d Curious if you get it resolved. Also check out GM-trucks.com if you haven’t already. Seems to be way more traffic at that forum.

 

Not resolved yet, thx for the heads up on the gm truck site

 

When you replaced the pressure sending unit did you also replace the cylindrical screen under that?

Have you tried a heaver-weight oil, wouldn't hurt with 128K miles, like a 10W-40 ?

We have 2005 Yukon 200K miles with fine actual oil pressure on the gauge, but occasionally get "oil pressure low" wording for a few seconds on the driver command screen, or whatever GM calls that. So since the engine has not self-destructed over the last 6 months, I believe the pressure gauge reading and just figure that the computer doesn't think oil pressure rises fast enough on start up so momentarily gives that error message. So on that I haven't done anything on that yet except change the oil and the brand of filter.

 

They don't seem to have section for '07 'burbans.

 

SDfromSD might mean trucks with same engine. For example, my 2005 Yukon Denali has the 6.0 engine, my 1994 Suburban had the 5.7 engine.

 

Did you check the oil pressure with a mechanical gauge?

 

Yes, please read the OP. Mechanical gauge, screen, O-ring, pressure relief valve, new pump (high velocity), and new camshaft thruster plate. Either done or replaced. Engine runs smooth as a top. Need something new here, please.

 

Have now replaced the rod and main bearings and still has not resolved the problem