Viscosity @ 40°C a predictor of Cold Pumpability?

[ka9mnx]

I think what hasn't been mentioned is the VI of the oil will effect it's pump ability (slightly).

 

[ZeeOSix]

Some people here obsess over a 3cSt operating spread for a 30 grade, but don't seem to care too much about 100's of cST spread at extreme cold temps as long as it had the proper "W" rating because the manufacturer said it has a given rating and is rated to pump at a given temp.

Because when the oil is cold and thick there will be plenty of MOFT due to the visvosity. But a small difference in viscosity when hot can make the MOFT change enough to make a difference in wear protecton headroom. The thinner the hot viscosiy (specifically HTHS viscosity), the lower the MOFT, and the closer to metal-to-metal contact.

 

[ZeeOSix]

I think what hasn't been mentioned is the VI of the oil will effect it's pump ability (slightly).

Yes, and that should be reflected in the W rating.

 

[SR5]

Some figures from Castrol Edge products sold in Australia

Edge 10W-30 (API SN/CF, ACEA A5/B5, ILSAC GF-5)
Vis 40C = 66.2 cSt
Vis 100C = 10.47 cSt
Pour Point = -36C
HTHS = 3.2 cP

Edge 5W-30 A3/B4 (API SL/CF, ACEA A3/B4, BMW LL-01, MB 229.5)
(Note Castrols says: "Passes all engine test performance requirements for API SN and SM but exceeds Phosphorus limits for those classifications.")
Vis 40C = 71.8 cSt
Vis 100C = 12.0 cSt
Pour Point = -36C
HTHS = 3.6 cP
Also it has a TBN = 10.2 and UOAs show about 1000 ppm ZDDP

Anyway both have the same pour point, yet the thicker A3/B4 oil is the 5W30, while the thinner A5/B5 & GF-5 oil is the 10W30. All figures from Castrol.

 

[kschachn]

Because when the oil is cold and thick there will be plenty of MOFT due to the visvosity. But a small difference in viscosity when hot can make the MOFT change enough to make a difference in wear protecton headroom. The thinner the hot viscosiy (specifically HTHS viscosity), the lower the MOFT, and the closer to metal-to-metal contact.

This is a good point. People really don’t understand how thin oil will get when it’s hot.

MOFT always wins.

 

[Jetronic]

Yes that is what I am trying to do to see which is the easiest to pump at a given low temp from a sample of oils with the same W rating.

Some people here obsess over a 3cSt operating spread for a 30 grade, but don't seem to care too much about 100's of cST spread at extreme cold temps as long as it had the proper "W" rating because the manufacturer said it has a given rating and is rated to pump at a given temp. So the inverse of that would be, why care if its a 9.5cST 30 or a 12Cst 30? Hey that same manufacturer said it performs as a 30 grade why care?

One of them will not even hace 3 cP HTHS, the other could be 3.5 cP. It's a big difference if your engine requires 3.5 cP minimum. xW-30 is the grade where just buying whatever can bite you the most from a viscosity standpoint.