Looking for oil recomendation

[supervc10]

Hello my fellow 928 owners, I am new to my 928, I have owned a 924 turbo in the 80's but this car is so much more! - anyway I have been looking to go synthetic, and would like to use Mobil 1, although not committed to this brand, i have been looking at their web site, and they recommend 0w40 which is straight weight oil, I run straight weight oil in my airplane (piper aztec) anyway i would like some owners input as to what i should be using - Thanks - Tom

[Danglerb]

As far as I know nobody has had an engine failure due to using the wrong brand of oil. Of course Porsche owners don't want good for their babies, they want best, let the hijinx begin.

Mobil 1, what I used for years, supposedly formulation changed this year.

Some people are having low oil pressure warning lights come on with the new very low viscosity low friction oils. Long discussions are around related to this, summary is that it isn't clear what the low pressure warning means except that 928 motors are 20+ years old and not put together as tight as modern engines. Oil pressure isn't what protects the motor, flow and film strength protect the motor, but low enough pressure and you get lifter noise, so nobody likes it.

Some have switched back to a higher viscosity oil, but some are also looking into the internal oil pressure regulation system to see if problems with it exist.

Any engine the leaks as much as a typical 928 should run synthetic since it stinks a lot less.

I now use Rotella T synthetic from walmart, but its just oil.

Confusion about oil, oil specifications, how oil works, what the numbers mean, formulation, generally complicates a discussion among hobbyist users like ourselves. I'm not sure its worth the effort to drift away from 15w50, YMMV.

[12magnum]

supervc10 I run Mobil 1 20-50 in my 86 928. I run Mobil Jet Oil II in my aircraft. I think Mobil 0-40 is too light for the 928- however I do run it in my mercedes.

[sonett3]

Mobil 1 15W50 or Royal Purple both will work well. The royal purple is thicker...I do not care for the zero weight oils...they are very thin.

[Fabio421]

I run Mobile 1 0w-40 in my 84 928 and I have 3 1/2 bar at idle and pegged gauge otherwise.

[Louie928]

You might want to check your 928 owners manual for Porsche's oil viscosity spec. The Lycoming oil viscosity spec probably plays a big part in choosing oil for your Aztec.

[Normy]

Your Aztec's O-540's require a straight-weight for the same reason that my lawnmower does: these engines primarily work within a small rpm band.

Aircraft engines are required to make mazimum power for long periods of time, and generally have a required warm up time. If you consult the AOM for your Aztec I'm sure that it will tell you not to apply takeoff power until the oil temperature reaches the green band. Normally, that's before you even reach the run-up area, but on a cold morning in Michigan then you might have to wait for a little while.

The reason for this is that cold oil doesn't flow, it tends to build pressure. The oil pump produces pressure that is mechanically demanded- that is, the oil is forced into the bearings. If oil flow is blocked, since oil is not compressible, then either the pressure relief valve will open or one of your oil lines will explode. Since the bearings in 9.0 liter air-cooled flat six engines tend to be built with generous tolerances, it only takes a few minutes of idle operation to reach "green band" temperatures. But here's one thing your Porsche will probably never experience: Full power for several minutes, then continuous 75% power for several hours at continuous rpm. THAT situation requires a thick oil- I think that most aviation engines require straight 50 weight ashless-dispersant oil after the first 50 hours in order to provide sufficient oil pressure at high temperatures under these conditions.

Your Porsche might be driven hard, but it doesn't see that sort of use! That is why you need to use the oil that is recommended in the owners manual in both your 928 and your Aztec. For the Porsche, I recommend Mobil Delvac 1300 in 15W40; Doug Hillary over on Rennlist has done an AMAZING job reporting on all of his oil condition reports, straight from the laboratory, while running this stuff for upwards of 14,000 miles.

Best of luck!

N