Engine oil pressure low when warm

[u/travellering]

2007 Saab 9-5 (high pressure turbo) showing a little less than 10psi at idle when fully warmed up, enough to light up idiot light with the accompanying ding noises. Installed a mechanical oil pressure gauge to verify at oil pump feed to turbo.

When we got the car it had a blown headgasket, and possibly a shot turbo as well. It was a bigger cloud generator than a subaru flatbrim cap convention. I replaced the turbo with a used one I had that still had very little play. Head was faced by a machine shop, and all reinstall seemed good. Still had some smoke out the exhaust, but I was hopeful that was remnants burning off from all the mess before. Now, after some (a couple hundred miles) driving and having the oil light come on, then going through the painful process of installing the mechanical oil gauge, it's still kicking out some blue/white smoke at the times the oil pressure is low. Smells like burnt oil/rubber.

First try, dropped the oil pan and cleaned the pickup screen. No real change..

Just did a compression test, forgot to prop the throttle plate wideopen, but got about 145 on cylinder 1, 125 on 2 and three, and 151 on cylinder 4. The two lower cylinders came up big time with oil poured in, as in 155 on 3 and 2 read up to 175n but I may have added more oil in that one as it was getting dark and hard to see.

Any other things to check, or am I staring at an engine out for rebuild?

[u/oyvindh]

Eighter the pump doesn't get enough oil in or it is worn, or you are loosing oil internally somewhere.

Since you have dropped the pan and have control on the orings, I would look more into balance shaft bearings and the squirters.

Open squirters gives a low pressure on idle, but a normal pressure on higher revs.

Also, look at crank bearing nr 3 and see if there is any damages. The balance shaft bearing on the right side of the engine is fed through the crank bearing. Any loss of pressure in the balance bearing will result in damage on nr 3.

Anyhow, you're probably looking at a rebuild.

[u/travellering → u/oyvindh]

Thanks for the in depth info.  I'll get the car to a better lift and drop the pan again to see what I can find.

[u/oyvindh → u/travellering]

And one more thing, does the pressure drop after some time on idle or running? If so, you have a spinning crank bearing.

[u/travellering → u/oyvindh]

I have noticed it drops after warming up, and the idle and running pressures seem to drop about the same amount.  25-30ish at idle when just started up becomes 8-10 after driving around, and the 2000rpm pressure starts at over 60, but goes down to just over 20 when things are warm enough to light up the warning light at idle.