|Ken(Ark) said: (quoted from post at 22:09:12 04/07/13) |
Whats up with the cold viscosity of the 15w40 ? Those numbers look like straight 40 ??
Shouldn't the cold (15w) be somewhere between the 5w/10w and the straight 30 ?
62.5 - 69.8 - 116.0 - 87.0
No because the 40C measurements are not how the the SAE cold weather gradesare assigned. The cold weather grades are determined by viscosity measurements at much colder temperatures (-20C to -35C). The 40C/100C measurements are the input values for the industry standard method of computing full engine oil viscosity curves (ASTM D130). That graph is produced by feeding actual product data for Valvoline All-Fleet engine oil into an online ASTM D130 caclulator program provided by Robert Widman (Widman Oil)..
Because oil viscosity changes exponentially with temperature a non-logarithmic graph can't visually separate the curves over the entire temperature band very well and I only provided the upper end on the graph so you could clearly see the separation up there. Here is the sub-zero portion of the same curves rescaled so you can see the differences at that end. The surprising thing for most people is that SAE 15W40 is only a marginally better cold weather performer than a monograde SAE 30 and doesn't drop under the SAE 30 viscosity curve until around -10C. At or near freezing the SAE 30 is actually thinner.
This post was edited by TheOldHokie at 05:41:45 04/08/13.