5w- and 10w- convergence point

[JHZR2]

Hi, For this example take m1 5w-30 and 10w-30 oils. At 100C, their viscosity is almost identical. So the 5w- oil meets a CCS spec at one temp and the 10w- oil meets a CCS spec at 5C warmer temp. Around what temperature can we assume the viscosity numbers to begin matching up equally? Is the slope or the behavior of the viscosity line at all temps from the CCS line always different until we hit the 100C mark, or are they mostly identical, except at the low temperature mark? Thanks, JMH

 

[haley10]

This is an interesting question. I notice Mobil 1 10W-30 doesn't cold crank quite as easily as Syntec 10W-30 at my mild zero F temps, even though I know it has a drastically lower pour point and better cold flow pumpability. Even though we know that real syns will flow at the lowest temps. The 0W, 5W, and 10W ratings seem to have a big real world impact, even though they will all have similar pour points. Good question. Wish I knew the answer.

 

[heyjay]

I bet Mobil does have this graph as an internal document, but I've never seen it. Esso did cold flow tests a LONG time ago and graphed them. They converged at around -25 C and AGAIN at around 43 C. This was an old test so it probably has no relation to the current oils. Of course, you can apply intuitive process to determine that for COLD temps, all other things equal, the "0W" will be best, then the "5W" then the "10W." There are exceptions and this is not a set-in-stone fact. Example, I notice that Esso markets a synthetic passenger car oil: Esso SuperFlow Synthetic. It appears tailored for high temp use as the 5W-30 is borderline at -34 C. That is worse cold temp performance than Mobil 1 SS 10W-30, at least based on the few test points that Mobil used to publish. Jerry