Originally Posted By: wemay
I understand your position Shannow and can see the logic following through. But to CATERHAM's point, when a normal Joe who doesn't have a sickness for all things oil like us, reads on the bottle/online 'compatible with all other oils', he isn't going to do the research that may yield the theoretical study results presented here. He's going read and understand that phrase to mean, "can mix". He will then pick up his oil and place it in the shopping cart next to the barbeque sauce, milk and never think twice. Nor does the vehicle's OM warn said Joe against mixing. It becomes sort of a non-starter argument to ask for proof of this.
wemay, they are all compatible, to the point that nothing bad is going to happen...Joe will not waste an engine, I agree...
But nothing guarantees that the cold weather end of the oil, the "W" will remain in any mix...even the oil manufacturers have to retest that claim when they change basestocks in certain directions (like choosing a new GrIII)...Joe doesn not have certainty that if he NEEDS a 5W, he's actually got one...there's no test for that in any of the licencing.
As I previously stated, most people are operating in the "normal" operating range, and are unaffected by the extreme "W" end of the spectrum...you'll be fine.
I'll be fine...look at what's in my sig...I've never tested the extreme end of my blend because Oz is impossible ... I just can't claim that it's a "5W40", or that any blend similar IS a "5W"