Most of the engine wear occurs at startup. Thicker the oil, the longer it takes for it to circulate.
In my opinion, if the ambient temperature routinely goes above 100F, 10W40 may not be a bad choice, but for temperatures going upto to only 80F, 10W30 or even 5W30 should work fine.
Before my Mercedes, I did not give the Oil grade much thought. Used 5W30 year round in Indiana, in all of my vechicle which ranged from 94 Passat, 2000 Maxima, 98 Montana, 87 300ZX, 89 Galant, 82 Century, Taurus, Probe etc.
I belive that with the MB, all of us on this fourm have an emotional attachment and we pay attention to a lot of small details, and MB's can be expensive to repair if something goes wrong!! and we keep them for a longer time.
As far as manufacturer's recomendation, I do not think it means much. All modern engines are fairly similar and operate under similar pressures and temperatures. I do not belive that auto makers collect historic data or do extensive testing, as everything keeps on changing, the oils, engines etc. are under constant development. They probably rely on oil manufactures's data.
All they can do is guess. A good example is the Mercedes FSS system and the associated engine problems relating to sludge etc. Computer models can give an idea, but the real world has too many variables. It becomes more of an ART then Science.
As an engine gets older, thicker oil can be useful at that time.
The best recomendation would be to choose engine oil based on ambient temperature and driving style.
Just think of the temperature in centigrades, so SAE 30 would be good upto 30 deg C, same thing with 40 and 50. The number before the W (which stands for winter) means that due to the addition of polymers, the oil behaves like a thinner oil at low temperatures.
As far as brands, all are similar. In Oils, Polymer additives are a little different. In fuels, fuel detergents are a little different, but the basic product is the same.
Automotive suppliers supply the same componets, eg. from Axles to piston rings to ignition systems with slight variations to OEM's. A lot of the componets are developed by the suppliers. Same thing with the oils. I am sure that all major brands have pretty much the same product.
94 E320 58000 Miles
Last edited by zafarhayatkhan; 05-22-2003 at 03:36 PM.