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Originally Posted by Easy Rider
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Originally Posted by primal
Why exactly? At temperature a 5W-40 oil will have the same viscosity as a 10W-40 oil.
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No reason, exactly. I'm just blowing off hot air. :shocked:
In that kind of climate, you probably should have a 50 as the top number.
They both "should" act like a 40W at high temperatures but maybe not exactly like and maybe not exactly the same.
I am not an oil engineer but I have looked at a LOT of owner's manuals for all kinds of vehicles and the recommendations for 5WXX and sometimes even 10WXX oils stops at the upper temperature ranges. I don't know why EXACTLY and I don't especially care. If you DO, maybe you should ask an engine manufacturer. |
At extreme hot temps the lighter oils will break down sooner and cause engine failures. Also some bikes(especially air cooled bikes)will run at higher temps which affect oil life.