0-w40 as a substitute of x-w30???

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Oct 3, 2002
Could you explain me this: if synthetic 0-w40, for example Mobil SS, is better than say 5-w30 (as I read in several posts), why would they bother producing 5-w30, 10-w30 and 10-w40 grades? Why not just use 0-w40 for all these applications. Is it all about volatility? Otherwise, it indeed has better cold flow and higher high temp. film strength and doesn't contain too much VII (again as I understood from some posts). Any other reasons
They have to produce 5w30 since it's probably the best selling viscosity out there right now.

Even if us oil experts know that the 0w40 is a better oil, the average motoring public does
not know this. They just follow what their owner's manual says.

It's in a company's best interest to offer as many viscosities as possible in order to increase
their market share. As much as I don't like 5w20, I'm surprised more oil companies don't make it, since both Honda and Ford (foolishly) recommend it for almost all of their new cars.
But then why don't they put a label like "Can be used for any applications requiring 0-w30, 5-w30, 10-w30, 10-w40"?
And is there a reason why all the "oil experts" don't use it instead 10-w30?

Oil companies make their lubes in the standard SAE grades recommended by engine manufacurers. For the past 10-15 years, the vast majority of US and Japanese manufacturers have recommended 5w-30 and 10w-30 grades for gas engines and 15w-40 grades for HD diesel engines. European engine manufacturers have continued to recommend a variety of SAE grades, depending on the ambient temp range the vehicle is being used in.

The M1, 0w-40 is made for those European vehicles that recommend an oil meeting the ACEA "A3/B4" and VW 502/505 specifications. If you are experiencing oil consumption or oil pressure problems running the M1 5w-30/10w-30, then the 0w-40 would probably help to some degree. It runs about 20% thicker in terms of high temp, high shear viscosity - this reflects the thickness of the oil in the bearings.

The additive chemistry of these three formulations is virtually identical, so I would not say the 0w-40 is necessarily a better product. All things being equal, the 10w-30 is going to be the most thermally stable and it's properties should change the least with use ....
You got me thinking. Next timken test day I'll do M1 TS 10W30 (no 0/5W30 here) and recheck TS 0W40. I'd be surprised if the 10W30 is as good. Hopefully M1 SS 0W40 and SS 10W30 along with CI-4/SL version D1 5W40 will be here too. Really looking forward to testing this bunch!
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