928 at last

I've used Brad Penn Racing "The Green Oil" for a decade and thousands of miles. ZDDP where we need it and no issues. Changed once per year.
Likely a bit more expensive than the WalMart alternatives, but no-one ever said maintaining a Porsche was a WalMart level financial commitment.....

FredR

John,

My circumstances are somewhat different to you folks in that I have very limited choices when it comes to lube oil selection. 20 years ago when I purchased my late S4 I ran with a Castrol synthetic lube that had a viscosity rating of 10w60. That mysteriously disappeared off the local market and then I managed to get Redline 20W50 from Dubai for a few years and then that source "disappeared". I then lost my S4 in a big smash and a year or so later "the phoenix rose from the ashes" with the motor transplanted into my current GTS chassis that now has some 95k miles under its belt. The motor was solid, we removed the heads, lapped the valves and resealed the motor. This was done as "a project" by the local agents at a very reasonable price. When the car was ready I took for it for a test drive, the motor felt great but this was during the hot season and after the motor was fully warmed up I noticed the oil pressure at idle was something like 1 barg and that scared the poo out of me. I drove the thing back to the dealers knowing whereas Mobil 1 had been used, I had not checked what viscosity was used. upon return to base I was advised they had filled with 0W40 and my brain flipped. To be fair, the agents told me they had checked with their heirarchy and that this oil was suitable for use in the 928. I politely said "no way" and tried to find a suitable brew. The best option I could find at the time was Castrol GTX. A year later, next oil change I could not even find that. After some research I decided to fall back on Shell Helix Super that is a API SL brew. This supposedly should be suitable for engines of our period and earlier API specs are just not available.

I then started doing some research that suggested STP oil treatment was a good source of ZDDP and more to the point, could add a little to the viscosity index and this help the oil pressure at idle a little. The lowest temperature my motor ever sees is about 17C so no cold starts. The oil pressure is generally solid at 2 barg on most hot days and on one occasion when I took it out on a "scorcher" it dropped a little below the 2 barg mark. I floated this approach on the list for opinions and got a reply from the Buchanan boys down under who told me they did exactly the same thing on the 928's they look after and that was good enough for me.

Given the choices you have such approach is not really necessary and mileage covered was never a concern in my case ad probably should not be in your case as the alusil bores seem to swallow such miles effortlessly unless premature damage of some kind has been done to the motor and then you would have much greater issues to deal with- hopefully not the case.

The STP treatment has been around longer than me and I first used that stuff in my ancient technology British motorcycle engines back in the days when lube oils were not as advanced as they are today. That the stuff is still marketed and widely available suggests that its use is not likely to do any damage or they would have been dragged through your courts long since. If I had your choice of available lubricants most likely I would not take this approach but as I can tell it seems to work fine. Last time I had the cam covers off a couple of years ago the cam lobes looked perfect and so is my oil pressure.

Trust the above of interest.

SwayBar

There is no need for an additive if one uses a quality oil, and there are plenty of them.

Do a Google search, and you'll find that's what the industry oil-guys say.

Along those lines you'll also find that adding additional ZDDP is counter productive. Just because other's have done it with no readily-apparent issues doesn't make it a good practice.

The same can be said for using a race-oil in a street engine. It may sound cool to your buddies that you're using a 'race oil' in your Porsche, but the reality is that's the last oil you'd want to run in a street car.

Don't over-think it and just use any good street-oil and be done with it.

andy-gts

I use 20-50 wt with 1300+ on both zinc and phos, AMSOIL Z ROD 20-50 been very happy

jschiller

Yes Fred, very interesting. I presently use Castrol TWS 10W60 in my M5 which is priced about the same as "race oil" (ca, $15/qt). Do you think that is a better choice than the Mobile1 15W50? I'm not trying to reopen the "Which oil to use" debate again, just wondering if the greater viscosity range would be of any use here in Florida where it never freezes or gets much above 100 F.

FredR

John,

Had it been available for me to use I would not have hesitated to use the Mobil 1 15W50 variant providing the ZDDP content was adequate as that is essential for the flat bucket tappet configuration in our engines. I doubt there is a specific need for you to use that Castrol variant but I would think it should also be fine. I seem to remember BMW specified nothing but the Castrol lube for your M5 [very nice engine/car that model series]. Basically you are spoilt for choice and doubtless you have some excellent recommendations in this thread. I was very happy with both the Castrol and the Redline when I could get them.

GregBBRD

Unless you have a specific reason to use an "engine cleaner" (lifter noise), just use the proper viscosity oil (15-50 or 20-50 unless you live in a very cold climate), with ZDDP over 1100 ppm.

If you have lifter noise...which is generally caused by deposits (black junk) on the check ball seat of the lifter, Swebco 502 is a good "solvent" and seems to work very well (I have no experience with Rislone or any other additives....I never had to find something that works better than Swebco.)

Any engine "cleaner" is going to "rinse" loose gunk.....that's why it is used. If you have an old engine with high mileage and you use a cleaner, I'd suggest changing the oil and filter soon (250 miles, maximum), after using any product like Swebco.

Lifters have internal "sludge" shelves. Crankshafts have blind oil passages that are "sludge traps." Cylinder heads have blind drillings that collect sludge. Loosening the sludge in these areas will put that sludge into suspension (and in the case of the crankshaft "sludge traps" run the thick, hardened, gunk directly to the rod bearings), which can damage the bearings.

How much "gunk" collects in our engines?

I disassembled a GTS engine with just over 100, 000 miles (which had TERRIBLE looking rod bearings), a couple of weeks ago, and tried to see if I could clean out the "sludge traps" without removing the "plugs". (I do this, commonly.) Huge "wads" of black gunk came out...1/4" x 1/4" "chunks" of hardened, abrasive, metal ladened, carbon-like material. After an hour of fussing with the crank, I still did not have two "throws" (much less the other six) clean and gave up. Off to the crankshaft shop, for removal, drilling, and tapping of the galley plugs, so the blind holes could be cleaned.

Would an engine cleaner have hurt this engine, before it was taken apart? I've got no idea, but I do know the only path that gunk can go, if loosened....straight to the rod bearings!

In short, only use an "additive" if you have a specific need....don't "toss" in additives for the shear "what could it hurt" sake. Think about what you are trying to accomplish and what ramifications your action might have.

If all you need is an oil change....change the oil.

jschiller

Sounds like sound advice. I think that's the approach I'm going to take.