mj1pate

Yes, I've perused the myriad oil pressure threads, and my situation is a bit different.
The last oil change was about 6 weeks ago, with the usual 10W-40 full synth. I used Castrol and I believe that I've used Castrol prior to this.

The oil level is fine.

After starting up, the oil pressure is immediately 5 bar.

at idle, the reading is consistently ~3 bar. No worries

After reaching (and holding) normal operating temp for about 15 minutes, the oil pressure (any RPMs above idle) begins falling to just under 4 bar. I can't make the oil pressure reach much above 4 bar, at any RPM. This is a new development since the last oil change, but this situation did not begin immediately after the last oil change. i.e. I can't directly say there is a correlation.

Likely culprits? Why would oil pressure drop only when above idle, after reaching normal op temperature?

I have new springs that attach above the oil sensor, that I am prepared to install. The sensor has about 18k miles on it. I don't yet have a new regulator in hand. How do the springs and regulator play together? This doesn't sound like a sensor failure, does it?

Hilton

That would scare me.

Your oil is thin for a 928 - maybe try changing to 20W50? (or 15W50 depending on your climate). Also before re-filling with thicker oil, cut open the filter and check for shiny bits (bearing debris).

JHowell37

My '85 does almost the same thing, and I use Amsoil. For these engines, the spec is 5bar at 4000RPM, with an oil temp of 80-100C. Now we've got the same engines and transmissions which means that at 60MPH, you're turning about 2100 RPM or so. So just cruising, you're not going to be at 5bar. I use 20W-50 and mine is just above 4bar. Are you in a warmer climate? You can try switching to a higher viscosity oil. I wouldn't lose too much sleep over this.

sidehatch

Thank god someone chimed in i have a 89 and this thing never goes to 5 bar mabe up at high rpm and at idle it actually goes down to 2 to 2 1/2 bar i think shes ready blow ticking time bomb.

blown 87

Have the plastic plugs for the oil galleys been replaced with metal ones?
If the have the plastic ones I am willing to bet they are bad.

Mrmerlin

a quick test for metal is to run the engine, pull the dipstick and drip some of the oil onto a black piece of cardboard then go into the sunlight look for tiny metal shavings.

Rob Edwards

So I'm a little paranoid on this subject lately, but my GT pegs 5 bar regardless of temp at anything about 2500 rpm, and drops to 2.5 bar at hot idle. I'm using Rotella 15W-40 Dino oil. If it were my engine I would at the very least cut open the oil filter, and spring for an oil analysis and see if you've got any bearing metals in the oil. Badly increased bearing clearance will drop your hot oil pressures....

How many miles on the engine, how regular are your flexplate releases, have you ever done the rod bearings, and have you had the valve covers off to look at the oil galley plugs?

Most likely it's fine, but checking a few things is cheap insurance: (I paid a lot for this picture, gonna use it as much as I can..

mark kibort

all my healthy 928 engines have raced for many years and miles. All of them ran 2 -3 bar at idle, even on the hottest of days, AND, all were over 5 bar at 2-3000rpm, depending on the temp of the engine oil (or the extreme-ness of the conditions) at near 260F (during the hottest point racing) im still at over 5 bar at over 3-4000rpm and pegged above that. If not, there might be an issue.
certainly change that oil out to the 20-50 and see if there is a difference, and take the advice to cut open the filter and pull it apart to see the paper filter and any metal bits that might be there.

Knock knock. (just in case)

sidehatch

If there is a small amount of metal what is happening,and what needs to be done?

mj1pate

OK....Good ideas. This came on relatively sudden, with no other symptoms. Flex plate is flat with zero additional travel of the drive shaft through the flex plate clamp since the last time I checked. The crank end play was in spec at the last check (4k miles ago) and the engine cranks like there is no tomorrow. I'll report he results of changing the oil regulator springs, the oil filter dissection and the (possible) change of oil viscosity results.

sidehatch

If there is a small amount of metal what is happening,and what needs to be done?Can i drive if theres metal?

Rob Edwards

Sure, just keep it under 2500 rpm, and pull over, stop the engine and let it cool completely before going up any hills greater than 100 feet tall.

sidehatch

So that means if theres small amount of metal in the oil,the engine is shot?

mark kibort

If you cant get oil pressure to over 4 bar, especially if revs are over 4k, you either have a shot motor, or the guage is bad. (to a lesser chance, the oil is the wrong viscosity, but even warm, not hot mobil 1 gets oil pressure to 5bar at 5,000rpm! (joke)

Leon Speed

It's true!!!