But the owners manual for both of my cars....

... Porsche has introduced their Porsche Classic Motor Oils.
Two viscosities for classic cars:

The Porsche Classic Motoroil comes in two different versions: 20W-50 for all 356, 914 and 911 models up to the 2.7-litre G-Model and
10W-60 for flat-six engines from a displacement of 3.0 litres up to the 911 (type 993).

[4.bp.blogspot.com]

Glad to see that they are acknowledging what many of us have been doing for a long time: Use heavier blends for the older cars and for cars that have high mileage.

They ain't cheap, though!
$13.65/liter for the 20W50 and $15.95/liter for the 10W60.

Happy Porsche'ing,
Pedro

Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

---

Racecar spelled backwards is Racecar

"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"

"If you wait, all that happens is that you get older"... Mario Andretti

"Being second is to be the first of the ones who lose" ... Ayrton Senna

says nothing about high mileage. And for many cars of the era the engines are low miles as the engines have been rebuilt. Last but not least all of the cars from that era are air cooled and the blurb at the web site specifically touches upon this.

Here's a link to the web site:

[www.porsche.com]

My latest copy of the approved oils list still applies to Porsche sports cars from IIRC 1984 and newer and there's not one 10w-xx or 15w-xx or 20w-xx oil listed. The only guideline for which viscosity of oil to use, 0w-40 vs. 5w-40 is temperature related.

.... does list 10w, 15w and 20w as preferred for warm environments, defined as "typically above 50 deg F". Then came stiffer cafe requirements, and the push for longer drain intervals in Yurrup (which means leaving the oil in for a full year +, crossing seasons) and it magically disappears.

Grant

Grant

gee-lenahan-at-gee-mail-dot-com

Quote
grant
.... does list 10w, 15w and 20w as preferred for warm environments, defined as "typically above 50 deg F". Then came stiffer cafe requirements, and the push for longer drain intervals in Yurrup (which means leaving the oil in for a full year +, crossing seasons) and it magically disappears.

Grant

that refers you to the dealer for the final word on what oils to use.

And the approved oils list the dealer can provide you -- at any rate mine does when I ask -- does not have one 10w-xx, 15w-xx, or 20w-xx oil listed.

We all know they changed. But history often reveals intent, much like an incriminating email....

And in hot climates, why would one care if its a 5w or a 10w.... is a 5w in -20 deg flowing better than a 10w in +45 deg?

If not, its arbitrary, or at least incomplete. Oh, and the viscosity curves prove its not.

Grant

Grant

gee-lenahan-at-gee-mail-dot-com



Edited 2 time(s). Last edit at 05/10/2014 11:56AM by grant. (view changes)

I cringe when I put 0W-40 in my 993. I used to use Delvac 1 but I read something in Excellence that highly recommended against doing that. Not sure why? The only question now is where can we get that stuff at a reasonable price or are we stuck with the dealer?

in the south bay -- recommends running Mobil 1 0w-40 oil, which the 914 owner has since he bought and installed the engine. He tracks the car too, every chance he gets.

Then there is as I've covered before the Porsche approved oils list. This list of oils applies to Porsche sports cars from the mid-80's on and that includes all 993 models. Not one 10w-xx, 15w-xx, or 20w-xx oil is listed.

Unless one doubts Porsche knows what it is talking about any of the 0w-40, 5w-40, or even one 5w-50 oil should be fine for your 993.

If you doubt Porsche knows what is talking about then how can you then turn around a use a Porsche classic oil?

Before I jump ship from M-1 to P-stuff I need to see the level of ZDDP it contains.

(~6K) RPMs at the ring/cylinder wall interface? Its detergent properties compromise the ability of the oil to lubricate.

Also, immediately upon beginning service the ZDDP starts to deplete.

How fast does it deplete? Well, from a test diesel engine (Mazda 4 cylinder inline OHV) producing 86.5bhp (at 3K RPM) and 22.9Kg.m (at 2K RPM) -- which I note suggest the test engine's RPMs are quite a bit lower than those experienced by our Porsche engines -- assuming 100% of the ZDDP was active at 0 km by 4000 km the percentage of active ZDDP was down to 23.6%. At 8000km it was down to 15.3%. by 13200km it was down to 2.0%.

There's more: As the ZDDP level goes down carboxylic acid goes up.

So you have to run lots of ZDDP to have any meaningful benefit (and its benefits are highly questionable -- I mean I have to point out most automakers recommend an oil with reasonable levels of ZDDP and the forums are not flooded with reports of engine failures or anything else that can be attributed to the amount of ZDDP in these oils) when the oil has some miles on, yet stay below 6K RPMs to avoid the risk of ring/cylinder wall damage and as the ZDDP depletes builds up acid in the oil.

More on that benefit thing…

There's the question of just how well ZDDP does what everyone believes it does. Spectromicroscopy of tribological films from engine oil additives one of the conclusions from looking at surfaces using x-ray microscopes found this:

The morphology of the alkyl and the aryl films are very different. The alkyl ZDDP decomposed rapidly to give protective pads of about 1–10 μm in diameter. In contrast, the much lower decomposition rate of the aryl ZDDP yields much slower, more uniform, formation of phosphate after a lot of wear has already occurred. There is no evidence of protective pad formation.

So run high levels of ZDDP as if it is some magical elixir.

But wonder what's happening at the rings/cylinder walls at high RPMs.

As the oil accumulates miles, work out how much of the that ZDDP remains to do its magic thing.

Think about those increasing levels of carboxylic acid.

Then recognize the stuff does not appear to form any protective anti-wear layer on the very surfaces it is supposed to protect.

What an additive.

Used a quart every 900 miles after the "rebuild." Back then I thought that was high, but apparently it wasn't too bad.