I have a 92 230E, 100 kmiles. The viscosity chart in the car=B4s manual indicates that I should use a 10w-40 oil viscosity for the temperature conditions where I live.
However every lube shop I go, they recommend using 20w-50 viscosity because of the age / mileage of the car. They say that due to engine wear, a car with more than 60 kmiles should use a thicker oil.
It makes sense. It is just that this car does not show any sign of wear yet, at least the ones that I am aware of, blue smoke exhaust and increased oil consumption.
In that case, and according to what I know (though not much and just theory), the thicker cold viscosity (two times thicker) would make the cold oil harder to flow during winter cold starts, increasing the wear. Also the thicker hot viscosity would cause the engine to generate more heat (and hence be less efficient).
What do you think?
Thanks Marcelo