Quote:
Originally Posted by FirstToy
then why do car makers recommend 5W-40 or 10w-30 etc instead of 0w-40?
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They're several reasons:
- In the case of 5w-40 (who recommends that anyway these days ?) or 5w-30, it's because the 0w, as in 0w-30 or 0w-40 is hard to find. 5W-xx is easier to find.
- They assume that most people are going to use regular oil, not synthetic. In the case of multi-weight, regular oil (lets say 10w-30), the oil starts as a 10w oil and viscosity improvers/enhancers (VI's) are added to make it behave as a 30w at operation temperature.
The problem is that the VI's are a "wear item", that is they wear out and as/when they do, the oil stops behaving as a 30w at operating temperatures (the VI's are gone) and it's now a straight 10w and that
is too thin at operating temperatures.
So they're trying to protect the engine from the most likely damage (over time) that will happen to it and that is people will use regular oil and a lot of the clowns won't change it as often as they should.
If they recommended (and people used) say a 0w-30 and the oil wasn't change properly, it'd act as a straight 0w oil when the VI's wore out and that would hurt the engine more (they believe) than the excessive cold start wear that occurs when running the 10w-30 in the vehicle.
Fred