What is the best oil weight to run in a diesel in the winter? Also, when you see an oil can that says for example 10W40 what exactly does that mean? What the difference between the numbers?? When you talk about the weight of the oil does a lower number mean it's thicker or thinner??
The best oil to run is that which the VW calls for. Since VW has called for different oils for different engines in different years, it would only be a guess for us to make a suggestion.
Diesel oils are different than oils for gasoline cars. Make sure that the oil meets VW's specifications for the year of your engine.
As for the numbers, the first number is an estimate of how that oil will pour at a given temperature and the second number is the same for a warmer temperature. I don't remember the temps, but the first one is cold and the second is hot. The smaller the number the thinner the oil so the faster it will pour. A 10W oil is thinner than a 40W oil. All oils get thinner when they get hot.
You want a thinner oil when cold because it starts lubricating sooner. You want a thicker oil when hot because it lubricates better.
Note: a 10W40 will be thinner when hot than cold, but it will be thinner cold than a 30W and thicker when hot than a 30W.
All multi weight oils have additives to give them that property. Those additives detract from some of their abilities to do other things oils need to do and they also wear out as the oil is used.
Synthetic oils are generally better at maintaining their thickness by nature.
However use the oil weight VW recommends for your engine.
Alan,
You'll find the answeres to both your questions at
Jo Bo
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