Oil Pressure Gremlins

radicalfil · 08-24-2002, 08:44 PM

After just reading a few posts about oil pressure and oil viscosity I think I might have a problem. I wasn't aware that multiviscosity oil could pose a problem for my 72 911T 2.4 w/ MFI. I just change the oil and put in 10-40. The oil that came out was unusually thin 10-30.

As it is now I have very high oil pressure upon startup and until the engine reaches operating temp. +/_ 190 degrees. Then the pressure drops to about 35 psi @ 4000 rpm and < 20 psi at idle and occasionally barely registering at idle.

Within the past couple of weeks I drove through the valley up to the mountains in the extreme heat-100+. At that time the car was running pretty hot, 230-240. So I took it easy on the way back. Yesterday I drove there and the engine ran at about 220 degrees in the 80 degree ambient temp.

My uninformed observation was noticing that as the oil warms up the pressure drops. PREHAPS I should change the oil again, but I am confused as to just what might be the best oil for this recently rebuilt motor, <5000 miles.

phil

Jim Sims · 08-24-2002, 09:12 PM

First of all, in the summer you should be using 20W50 if you are using natural oil (dino oil). Second, oil pressure drops as the oil heats up; you should see between 10 and 15 psi per 1000 rpm when the oil is at operating temperature (a close to zero pressure indication at idle is also typical). Third, your oil temperatures are too hot. Is all your engine sheet metal in place and are all the hot air hoses in good condition and connected? Are the spark plug wire air seals in place? If all is in order and since your engine was recently rebuilt (hopefully all the barrels are in the right orientation and the internal baffling is in place and appropriately updated by trimming) it and the engine mounted oil cooler should be clean. You likely need to mount an external oil cooler if you don't have one. If you do have one, you need to check that the lines under the car on the passenger side are hot (hot oil going forward to a right front fender mounted cooler). Cheers, Jim

radicalfil · 08-25-2002, 07:08 AM

What is the recommended oil viscosity for the winter season?

You mentioned that the baffles are updated by trimming. What is the trimming?

I probably will have to either mount an exterior cooler or just drive it around the coastal/cooler areas.

phil

Jim Sims · 08-25-2002, 07:14 PM

From the Technical Notes II (an Excellence magazine compilation of Bruce Anderson's monthly Tech Notes) Mr. Anderson refers to recent Porsche guidance about engine oils for 1973 and earlier 911's: For Summer or warm climates: SAE 20W-50, SAE 20W-40 or SAE 40; for Winter use or in cold climates: SAE 15W-40 or SAE 10W-30.

On page 176 of Bruce Anderson's "Porsche 911 performance Handbook" one may find a diagram of the air deflector or baffle modification. One removes a 1 " wide strip part of the way down one of the edges of the center four baffles or deflectors. Claimed to be worth 10 to 15 degrees F improvement in operating temperature.

Drove to Albuquerque and back this afternoon driving in a 911 convoy at 80 mph in 95 to 100 F air temps. Max oil temp reached was around 212 degrees F with a '76 2.7 mounting an external trombone type turnaround loop oil cooler. No A/C.

Cheers, Jim

radicalfil · 08-25-2002, 09:42 PM

Hey thanks for the info about ole dinoil!

I'll check out the B. Anderson blerb in that book. A little late for me unless some major malfunction occurs to modify those lil'
tini-tin-tins.

Maybe time to get serious about the external oil cooler.

Right now the next project is to mount the RS interior door panels on my car. Not to make it go faster just less space to collect junk, i.e. door pockets.

phil