[QUOTE=Flavor 987S;266560]
Quote:
Originally Posted by rene525d
It seems that the only porsche approved oils come in the 0w-40 and 5w-40 grades. No mention of the 10w-40 grades. QUOTE]
You are correct. Plus, Porsche also approves 5W50 in some brands.
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Porsche has typically "approved" a variety of products without any specific technical definition as to "Why?" The "N" rated tire is a perfect example; another is the use of a 196 F thermostat; both of which have been demonstrated time and again can be ignored with positive results. Oil weights over the last decade of so have been going towards lighter weights with no apparent rationale. Not that long ago, 10W oils were the "recommended" standard for use in arctic like climates; now 0W oils are the supposed choice for use in southern California or Texas; yet most people do not ask why. If one collects and examines the flow characteristics of various weight oils at low temps, you begin to notice there is not all the large a difference between a 5W oil and a 10W oil when they are cold; so why the big push to low weights, particularly when these light weight oils tend to show a lower ability to "stay in grade" under heat and shear? The answers to lie in the manufacturer’s need to get their CAFE ratings as high as possible. Some time back, the EPA changed the standards by which the OEM's develop their mileage ratings for fuel economy; previously, the OEM's had been allowed to use any oil for the EPA testing, and then the EPA discovered that they were using oils like 0W-5 (or lighter) for the tests to max the mileage, but recommending much heavier oils for normal maintenance. The EPA altered the rules to require that the test be run using the recommended oil weights. Porsche went to 0W-40; Toyota and Honda went to 0W-20, and so on.
Unfortunately, this move has sometime backfired on the OEM's, BMW and Toyota both had to change their oil weight recommendations after a large number of early engine failures pointed out the weight's shortcomings of the very low weight oils. When we saw 0W-40 Mobil 1 oil falling way out of grade after a couple thousand street miles in a "soccer mom" vehicle, we started looking for products that could go 5-7K miles under mixed street and track usage in a M96/97 and still pass muster. 10W-40 oils and particularly the Castrol Syntec did that well, while still allowing use in cold temps with no start up issues.
Just because Porsche “approves” or “recommends” something doesn’t mean they do it with your benefit in mind………..