Originally Posted By: 92saturnsl2
Originally Posted By: 69GTX
Good points. I've used both M1 5w-30 and 0w-40 in one of my cars. And for my typical cold start nearly all year round, the 5w-30 has the better low flow specs. Though at -40 to -35 deg C, the 0w would win out.
So many people blindly assume that 0w must be better than 5w, for cold temps.
I think with the acknowledged caveat that we are looking at oils within the same grade and classification (GF-5 for example), generally (not always) a 0w-xx will have a more gentle curve to it, due to it having to meet the CCS and MRV requirements for the designation.
Originally Posted By: 92saturnsl2
Couldn't be further from the truth. M1 0w-40 is thicker at 32F than M1 5w-30, and even M1 10w-30.
I would bloody well hope so, it is a 40 being compared to two energy conserving xw-30's. When you start getting down toward the limits of the 20w or 15w designation, you might see it thicken less, but even that's not guaranteed. We just know the other two won't pass CCS and MRV at -35C and -40C respectively.
Of course, I wouldn't call 32F cold. Location is important when making that qualifier. "Cold" in Florida means something quite different from "cold" in Winnipeg.
The OP listed his location as Canada and gave a floor temperature of -30C, which is the CCS limit for the 5w-xx designation and the MRV limit for the 10w-xx one. At that temperature the 0w-xx, even in a heavier grade, is almost a guarantee as to ending up on top, which can be easily estimated by taking the CCS and MRV values and cutting them in half to get their 5w-xx versions, and in half again to get their 10w-xx ones.
Originally Posted By: 92saturnsl2
Castrol makes a 5w-50, it will be far thicker at 0-32F than any 5w-30 or 10w-30.
Yeah, being an xw-50, of course it would be.
Originally Posted By: 92saturnsl2
If I were concerned about cold starts primarily, I'd choose a good 5w-30 or 0w-30 that is is on the thin side-- generally those are the ones without ACEA A3 rating.
Unless of course your vehicle calls for an oil with an HTHS >=3.5cP