[mike944]

I use synthetic in all my cars, Mobil 1 in my 944, and 968. No noticable leakage out of the 944, but then again, it has new seals. My 968, well that's another story from a leakage standpoint. I think that's my own damn fault though, i didn't get the oil pan gasket on really well, and that's where it's leaking. Hard to say whether it would leak with dino-juice or not.

I just read a really good, technical article this month on motor oil, it was either in Panorama, or 9 Magazine. Hey, what can i say, i'm an Engineer, i love technical articles on anything! To summarize the article: The wider the "points spread" in oils, the more Viscosity Improvers that have to be added. Viscosity Improvers, without going into detail, are additives, that do NOT have any lubricating properties on their own. The more Viscosity Improvers you need to use, the less oil you're getting. At lower numbers (5, 10) more Improvers are needed for a given "points spread" then at thicker base numbers. A 20-50, while still having the same 30 point spread, has less Viscosity Improvers than 10-40.

The advantage of synthetic, is the base oil stock is more stable, over a wider temperature range, therefore for a given "points spread" significantly less Viscosity Improvers need to be added, and you get more oil. In addition, the synthetic oil base itself has better properties.

I think many people would agree, I would stay away from 10-40, there's too many additives. Depending on your climate, i would use 10-30 in the winter, and 20-50 (or 15-50 synthetic) in the summer.

Don't forget that the 944 series is designed to use much thicker oil, than most modern cars. Use a grade that either matches, or covers the reccomended grade numbers in the owner's manual for the temperature range you use the car in.