Oil Recommendation

[Draol]

I have a 1996 911 cabriolet, model 993. In the summer, I have always used Mobil One synthetic oil 15W-50. This year I changed dealerships and when I took my car in for its pre-summer oil change, the dealer said that Porsche now recommended Mobil One 0W-40. I accepted what the dealer suggested, but then recently on a hot day in traffic, I noticed that even when reving above idle (in fact up to 2800rpm's), the oil pressure did not max out, but stayed slightly below 5 on my gauge. Above 3000 rpm's, the pressure returned to maximum. Since then, I have not been in much traffic on hot days and have not noticed more problems.

Is this issue one that has occurred before? Is it something that might just affect air cooled engines? Is the recommendation from the dealer aimed at those who don't use a different weight summer oil? My dealer has nothing to say except this is what Porsche recommends.

[Loren]

Sometime last year Porsche issued new TSBs that changed the recommended oils listing for all (90's and newer) cars. On that list they no longer recommend Mobil 1 15W-50 but do recommend 0W-40. The complete approved oils list is about 8 pages long to cover all worldwide requirements.

It's hard to say why they changed, but I do know MB also changed about the same time... and that MB had some serious problems with oil sludging.

[mrmickeymouse]

The reason you saw the lessened oil pressure is because your oil thinned. I don't know about you, but thin oil is not a good thing.

I am sticking with thicker oil [boxster motor], oil is much more important to you then me, it play's a dual rule of lubrication and cooling.

If there is no justification for using 0W oil I would avoid it. Maybe Loren can tell us why he believes it's better, or maybe his opinion.

TIA

Scott

[ron in sc]

Below is a good discussion I had saved about oil. I did not write this so I can not take credit for it.

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!

[ar38070]

0W-40 improves gas mileage and consequently lowers emissions (thinner oil, less friction). I do not know how much, probably not much more than 1 mpg, but anything helps with regard to CAFE. I think that that is the major reason manufacturers are recommending 0W-40.

I will agree that for 90%+ of the porches out there, 0W-40 is okay. If your car spends a lot of time at redline (track or really, really agressive street driving, like redlining the car every 5 minutes) then 15w-50 is the better choice.

Oil consumption is also probably a bit higher too with 0W-40.

[stlrj]

Why not compromise and use 5W30?

[djantlive]

5w30 is too thin at high temp to protect engine.

[stlrj]

5w30 is too thin at high temp to protect engine.

That's what you might think but I have found it to be an excellent choice for my 86 3.2 and have been using it for 3 years now without any adverse effects. However, the benefits are better lubrication at startup where 90 percent of wear occurs as well as cooler oil temperatures which I find hard to beat! :cheers:

Cheers,

Joe

Edited October 1, 2006 by stlrj

[dshepp806]

5w30 is too thin at high temp to protect engine.

That's what you might think but I have found it to be an excellent choice for my 86 3.2 and have been using it for 3 years now without any adverse effects. However, the benefits are better lubrication at startup where 90 percent of wear occurs as well as cooler oil temperatures which I find hard to beat! :cheers:

Cheers,

Joe

On an 86? You must be kidding me? NO way on this Earth would I run that light of an oil in that engine..

Have you read all of the data at Pelican or Renlist?

And which 5W30 do you use?

Best,

Doyle