Carrera Mike

Here's PCA tech board answer. This topic has been and will always be subject for debate. IMHO, Joel has a good point regarding the Hydraulic Valve Adjusters

Q:
Is Mobil 1 0W-40 a recommended oil for a 95 993 in the USA for temps generally above freezing? I have been using 15w-50, but now 0w-40 is available and I am wondering whether 0w-40 is better. I know that it is the factory fill for 996s, but does it offer any advantages for a warm weather 993?

A:
The 15W-50 is for warmer climates and/or tougher service, and the 0-40 is for cooler climates. I hope I did not misunderstand the question. 0 will flow better at a lower temperature than 15 will. Likewise the 50 will handle the higher temps better than the 40 will. In warmer weather and on the track I run the 15-50, whereas I run 0-40 in my street car for the cold winter weather. So I would say 'no, it only has advantages for the colder weather'.

Since publishing the note above, I have additional information from Bruce Anderson and Peter Smith to pass along. Porsche is currently recommending the following in Technical Bulletin 1701, "Engine Oils Approved by Porsche":

Porsche's approved lists of oils appear in Technical Bulletin 1701, and they are all synthetic:

Castrol Syntec 5W-50 (G)

Mobil Mobil1 0W-40, 5W-40 (GL)

Sunoco Synturo Gold 5W-40 (GL)

Havoline Formula 3 Synthetic 5W-40 (GL)

Valvoline high performance synthetic 5W-30 (GL)
Note that Mobil1 0W-40 was not available yet at that point in time.

We are thinking that Porsche favors the 40 top weight over the 50 for street use because it is friendlier to the hydraulic valve adjusters (993 and 986/996) and other areas of the VarioCam valve train (986/996). In the case of the former, we have seen some of these newer cars struggle to achieve compression on startup in certain circumstances because the hydraulic valve adjusters are not pressurizing correctly.

So the revised answer is 'yes, it offers valvetrain advantages provided you keep the oil temperatures within specs'. In other words I will still run 15W-50 in my GT3 Cup car with the hydraulic valve adjusters because it is still heavier duty service than a 0-40 would be best for. But on the newer street cars the 0-40 is probably better if your climate is not hellaciously hot and you don't overdrive the car.

Joel Reiser / Bruce Anderson- PCA Website 2/02

KINGSRULE

Once again I'll tell you guys;
993's came filled from the factory with Mobil One 5w40.
5w40 Mobil One was not available in the US when 993's were built.
So are you going to listen to all the "experts" out there or follow the factory? My feeling is that for the longest time Mobil One here in the US was only available as a 30 or 50 weight oil so the "experts" went with the 50 weight (15w50 to be clear) because as we know "bigger is better"!
Now that a 40 weight Mobil One product is available is there any question which Mobil One product is the one to use?

0w40 is the right oil for 993's under all driving conditions.

Greg Fishman

I will bet the engine in my race car that it isn't!

914und993

0W-40 is probably the perfect all around choice for 98% of street driven 993s. I think it does have an Achilles heel that make it not so good for some owners, of whom there is an especially high incidence on the Rennlist forums.

To get a 0W-40, even starting with a synthetic base stock, you must begin with a rather thin oil, probably what would be the equivalent of a 0W-20. Then you add viscosity extenders to it, which are long chain organic molecules that unfold as they meet higher temperatures. This keeps the oil from thinning as fast as it would normally as it heats up, and allows it to have the 40 weight rating at 100 degrees Celsius.

One problem with viscosity extenders is that they aren't lubricants themselves, so their volume displaces the lubricating base stock, and the lubricity of the resulting oil is actually a little less. The bigger problem is that under high temperature, high shear conditions (high rpm!) these molecules are sheared apart and destroyed - over time. As these molecules are destroyed, the oil becomes thinner at high temperatures, so what was originally a 0W-40 oil starts approaching the viscosity of the original base stock - the 0W-20 stuff. This is not good for continued use at high temperatures and loads.

This is probably unlikely to happen to 0W-40 to a significant extent under normal street use within a recommended oil change interval. But if you drive your car hard on the streets of Phoenix in the summer, or regularly take your 993 to the track for DE events, 0W-40 might not hold up very well. This is why track guys like synthetic 15W-50, which has a higher viscosity base stock, and uses little (maybe none) added viscosity extender and will provide proper protection to the engine under "race" type conditions for a longer time than 0W-40.

So you see why Mobile 1 0W-40 might be the perfect oil for GJ, but not at all the right one for Greg's race car. There are no simple answers!

Chip

Speedraser

You can hear it when hydraulic lifters don't pressurize -- I've never heard it in my 993.

Greg Fishman

I have heard this a time or so on my race car at start up when it had sat for a month or so. Took about a minute or so for the clacking of the lifters to subside. In my street car it occured once when new and the lifters were replaced under warranty.

Dick in TN

What is your collective thinking about Castrol 5W-50? Wouldn't it provide better low temp flow than Mobil 15-50 while at the same time equal high temp viscosity?

GrantG

Dick - The Castrol 5-50 is my choice

Steve Weiner-Rennsport Systems

I'd just jump in here and offer that we use 15w-50 Mobil 1 for all air-cooled cars.

Please bear in mind that the oil temp guage only samples & displays temperature at a single point in these "oil-cooled" engines and its far hotter in other places.

0w-40 is the right stuff for the water-cooled 996's equipped with Variocam that require the thinner oil for proper camshaft dynamics. Porsche also recommends the thinner oils for fuel economy; something very important for Federal CAFE compliance.

IMHO, the 5w-50 oils break down much faster due to being comprised largely of Viscosity Improvers that are the most subject to heat degradation.

tsjoel

Perfect timing on this thread for me. Yesterday I walked out of the auto parts store without oil because of confusion with all of the choices of Mobil 1.

GrantG

Steve W - Is the 15W-50 ok to use in really cold climates (below zero)? Also, I thought the synthetic Mobil 1 is not recommended for the older 911s, so I've been using the 5W-50 Castrol in my 993 in the cold weather (I change to 15W-50 Mobil 1 in the warmer months) and only use Valvoline Racing 20W-50 Dino in the 911 RS2.7 (primarily a track car that rarely goes out in the cold). Would you change this approach?

Rob993

The P-car dealer in my part of Canada only uses 5-50 Castrol since the first 993's arrived, and has been in my car since factory. In our driving season, the weather swings from 32 F to 90 F.

Rob

Carrera Mike

I'm gonna try 0W-40 Mobil 1 this winter. As Joel Reiser said, it can only do good for the hydraulic valve adjusters. I have replaced head gaskets recently so they should hold that thin oil real good. I'll keep everyone posted.

lexpilot

Based on Chip's dissertation would not 5w-40 be a better choice for summer street cars ? The premise being that the 5w-40 starts with a thicker base than the 0w-40.
Professor Weiner ?

Edward

Warning -- opinion alert (with a little bit of experience, anyway ):

I'm willing to bet that Porsche's "Factory Recommendations" are influenced largely on the economics and liability with regard to the Current production models. Testing oil is costly, especially if doing durabilty tests with various brands, viscosities, and over varying conditions. If you were responsible for the "bottom line," you would probably opt for the fewest variables possible with the hope of arriving at a "one-size-fits-all" solution --all manufacturers do this. As for liability, it's the current production cars still under waranty that the factory is most concerned with. Again, reducing their liability exposure weighs into the their "Official Recommendations." I like to think of all manufacturers' maintenence intervals on routine maintenence. Tell me those aren't motivated by the appearance of making the car appear "cheaper" to operate, and now car makers are even touting the "less maintenence" angle to help hawk their product. The "proper oil," just like the "proper driving line" or the "proper oil change interval" depends on many condition which vary as much as there are drivers. Thus, I personally consider all factory recommendatins along with my own experience, the experience of a few professionals, and the conditions at hand. In my mind, these are the most prudent steps for a maintaining a happy car over the long haul.

Edward