Low oil pressure, time for rebuild?

[staffanbe]

I have a 964 turbo -91 with apx 75000 miles.
My car got low oil pressure the other day, light came on and oil pressure got close to 0 according to the stock pressure gauge at idle, managed to keep 2bar at apx 3K.
Shut the car down and had it towed home.

Realized that I have seen the oil pressure go lower at idle the last couple of weeks, if I remember correctly it's usually 2bar at idle but lately it was around 1bar.

I checked the pressure valve pistons, and one of them had some shallow grooves. After changing oil filter, removing and cleaning safety and relief valve I started the car and had good oil pressure, thought I solved the problem but when the engine started to get warm the oil pressure started to get lower.

After about 10 minutes the car had trouble getting oil pressure in line with 1bar per 1K, and I shut down the engine when oil pressure got below 1bar at idle.

Tomorrow I will change pressure valve pistons and springs.
Is decreasing oil pressure with increased temperature a pretty clear indication of "time for a rebuild"?

Last thing I did before getting this problem was installing B&B headers which included getting a new oil line from the left side of engine to the oil tank.

Thanks
Staffan

[Eagledriver]

You should verify that your oil pressure guage is functioning properly. The sender could be going bad. Maybe hook up a mechanical guage and see if it reads the same as the cars guage. If the oil pressure is really that low then you may have bearings that are worn out and need a rebuild. You could also try a thicker oil and make sure there are no other problems. Changing the springs and pistons is a good idea. Could there be too much oil flowing to the turbo? I don't no much about turbo cars but maybe the oil flow is supposed to be restricted somehow as it goes to the turbo.

-Andy

[ischmitz]

First, lower pressure with the engine warming up is normal. Depending on the type of oil and the outside temperature you will see around 1.5 to 3 bar on idle with a cold engine. At operating temperature it should still be around 0.8 to 1.0 bar. Anything much less indicates a problem. A heavier oil might be a partial solution but it won't fix a wonr

Changing the springs will have little to no effect since the pressure relief valve is designed to open above 5 bar and the safety valve opens above 10 bar. Your problem is low pressure at idle. Both valves are closed at that point.

First, check with a mechanic gauge to verify the readings of your gauge. As Andy mentioned it could be on its way out. If your pressure is indead low then you most likley will have to dig into the engine. Bearing wear or a worn oil pump would be my first guess. There were other threads where low pressure at idle after a rebuild was traced back to a missing piston squirter.

Good luck and keep us posted,
Ingo

[staffanbe]

Thanks Andy and Ingo!
I will change springs and pistons today, I know it's very unlikely it will solve my problem, but stranger things have happened.

Since both the warning light and pressure gauge tells me the same thing I will measure with a mechanical gauge as the last resort because i will do a partial drop for easy reach. If that shows what I think it will I just keep lowering...

Thanks for your support!

[cstreit]

Definitely check with a mechanical gauge. I've eased a few troubled minds with one. In addition it's probably coincidental that you recently installed an oil-line, but check it anyway! I believe the oil-line for B&B's is the main pump intake... Could there be a restriction in it? (faulty line?)

Is it also possible that your pressure releief pistons are stuck open or that your oil was somehow vastly diluted. I've seen both of these. Eliminate all other options before cracking that engine open.

[staffanbe]

Thanks Crhis!

I also installed a new droptank for the turbo.
The new one doesn't have any ventilation, thinking about the possibility of air bubbles creating lower pressure, any thoughts about this.
The problem is that it didn't happen right away after the change.

The new droptank sits with only 1mm of air between it and the wastegate exhaust pipe, thinking that it might heat the oil (boil?) and create bubbles.

[cstreit]

Man I dunno, I'm not a turbo guy... However substantial bubbles in the oil/foaming could cause low oil-pressure... But it would have to be a LOT I would think...

[staffanbe]

Turned out to be a broken pressure sender.
I thought "idiot light" and pressure gauge had two different sources, but both are in the same sender.

Thanks for you support!

[ischmitz]

That's good news. The pressure sender puts out two different signals (one for the gauge and one for the light) but uses the same internal mechanism to sense the pressure. So if that mechanism is busted it makes sense that both the gauge reads low and the light comes on.

Glad you found it. It's a lot cheaper to replace than having to rebuild the engine