Originally Posted By: KrisZ
Lets substitute PYB for PP and at -35C we have M1:6,625 ....PP:9,000, the difference is much less.
But it is still 3,000cP, and the relative difference persists right up until whatever the crossover is
Originally Posted By: KrisZ
Now lets substitute M1 to Shell 0w30 and at -35c we have Shell:9,450 ....PP:9,000.
Yup, but you have to include CCS in your thinking about that as well, which we know for the 5w-20, was above the limit at -35C to classify it as a 0w-20. That's why it is nice to have both figures. I wish it was mandatory to include both on a PDS.
Also, you are comparing to a (much heavier) Euro 0w-30, which is like GC and wouldn't be cross-shopped here, that's why I chose the AFE 0w-30, as it is your typical PCMO style 0w-30. M1 0w-40 also has a relatively lacklustre MRV, but we know for CCS, it is under the limit at -35C.
However, you did bring up a great example with PP,as they actually list CCS for it. It is 4,000cP @ -30C. We know that the Shell 0w-30 is
Interesting the difference between the two tests eh? MRV tests pumpability, CCS is the Cold Cranking Simulator.
Originally Posted By: KrisZ
Petro Canada's synthetic 5w20 (9,100) is also thinner at -35c than their 0w30 (11,450).
Now THAT is a good find! As those are both PCMO's. So you DID manage to find an example, that is excellent, so I'll cede that one to you, victory sir! Did you notice their 0w-20 isn't much thinner either?
Originally Posted By: KrisZ
M1 ESP 0w30 is 26900 at -30C.
That's a typo. MRV has to be measured at the spec for the weight, so its MRV is 26,900 @ -40C, so 13,450 @ -35C, so a bit thinner than PYB but thicker than PP.
Originally Posted By: KrisZ
Like I said, it's not the same as the hot viscosity. Now why would it be like that? Why would the requirements only be for the maximum viscosity for the extreme cold spec, and be so specific as for the hot spec? Could it be that, as long as the oil is below the maximum, and is pumpable, there is little difference in wear protection during cold starts?
I don't think it is the wear, I think it is that it becomes unpumpable below that point, LOL! That's why I said earlier that the Cold Cranking viscosity (CCS) may be a better reference point, as the limit on it is much tighter.
Originally Posted By: KrisZ
I ask again, if it was so important, why such a variation between 0w oils. Why would M1 0w20 be 9,200 at -40C , M1 AFE 0w30 be 13,250 and M1 ESP 0w30 be 26,900 at -30C or 107,600 at -40C? Those ar pretty big variation in viscosity for oils that have the same 0w rating.
Well the limit is 60,000cP for MRV, so we know that last one is wrong, LOL! But for CCS, they all have to be under the limit of 6,200cP, which is a lot more stringent and they will be all a lot closer to that limit than they are to the MRV.
I think the "importance" thing is relative
but I know that I'd rather have the AFE 0w-30 in the sump (or the 0w-20, which I do have) than the others due to what I mentioned about cylinder lubrication earlier. Another good choice would be the EP 0w-20.
I don't think about it in terms of comparing it to hot viscosity, just about how much less it thickens as the temperature plummets; about keeping the oil as thin as I can as the temperature goes down. This allows better cold cranking and better splash lube in places that receive it. And better spray lube in areas that see that. This also, IMHO, means that there is less time on the pressure relief and less time on bypass, though that may be completely irrelevant in the big scheme of things, I just figured I'd mention it. My biggest "hangup" here is cylinder spray lube, which I think is a genuine thing to think about, as it is something that once an oil does get down to these extremely low temperatures and high viscosities, that may actually be affected
That's my theory anyway, LOL!