I'd like to know as well since I'm about to change the oil in my car for the 1st time. I think a lot of it has to do with how many miles you have on your car. So if someone could tell me as well that would be nice.
I've always wondered exactly what the numbers mean. Can someone explain what the first number and second number means? I assume the "w" stand for "weight" right? Also, my car was burning oil so the oil changers put in 20w50 because it is heavier and will burn less oil.
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w stands for winter. 10w30 is a multi weight oil. By adding viscocity modifers and improvers manufacturers are able to produce an oil that acts like a 10 weight oil when cold and like a 30 weight when hot. This improves circulation when cold, to extend engine life. Straight weight oils do exist, usually SAE30 but you only use it in the lawnmower.
The numbers are indexed values of viscousity classified at set temperatures.
The lower one at 20degrees celcius(68F) I think and the higher is at 100 degree celsius (212).
All non M-models come with Castrol SLX(?) 0w-30 here.
BMW recomends Castrol TWS 10w-60 for M-models. And that is what I use.
Low cold viscousity index is pretty much allways good. Makes sure you allways get lubrication from start-up. And it provides lower friction in the engine.
You want the warm viscousity index high if you drive the car hard and get high oil temps.
Race oils are usually 20w-60, they usually warm along time on idel/low rpms so the cold index isn't that important.
The wider the spread the more expensive it is to produce.
On my 1993 325 with 125k im using Lubro Moly 0w40 full synthetic oil, and im very happy about it, the engine revs smooth as butter and loose as a goose. Its great stuff, but its pricey. But i prefer spending 50 bucks buying the oil and changing it myself, so i know im using good stuff, that sending it to the 20min lube job..
any questyions ask
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