Quote:
Originally Posted by Cobb
I was reading something the other day that the larger the weight range was the more likely it was to sheer or loose that weight as the oil approaches the end of its life. So if you needed a 40 weight oil you were better off to buy a 20w50 vs a 5w40 or something to that effect.
The second example they gave was ow20 vs 5w20. They said the 5w20 would still hold its 20 weight at the end of its cycle where the 0w would drift to like a 15 or even 10 weight oil at operating temperature.
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I think that's only true for non-synthetic oils. Synthetic oil comes with that viscosity from the base stock, while conventional oil starts with a lower viscosity index, has VI improvers added, and then those get burned off and the oil thins out. I use non-synthetic and change slightly more often, my 1ZZ engine would burn too much of it between changes if I tried to extend intervals.