# Widman Viscosity Curve M1 0w40 vs M1 5w30HM

#### mahanddeem

See attached pic.

How does Widman Curve determine these numbers at say 0c? Intuitively, M1 0w40 (blue) having a higher viscosity at 100c than M1 5w30 HM (red), 12.9 vs 11.9, and almost the same viscosity at 40c (around 70) it would be reasonable to assume M1 0w40 thicker at 0c! Curve shows the opposite!

Why it shows at 0c M1 is less viscous than the HM oil?

#### Jetronic

Have a look at the viscosity index of both oils, I bet 0w40 has a higher viscosity index, which is an oils resistance to viscosity change. If 0W40 was already thicker at 0C it would be very hard to make the 0W anyway.

#### ka9mnx

One is a 0w and one is a 5w. Not a fair comparison.

#### mahanddeem

Have a look at the viscosity index of both oils, I bet 0w40 has a higher viscosity index, which is an oils resistance to viscosity change. If 0W40 was already thicker at 0C it would be very hard to make the 0W anyway.
This curve doesn't take into account 0w or 5w and it never cares.
It only needs to know the viscosity at 40c and 100c.
Curve is not "cheating".

#### mahanddeem

One is a 0w and one is a 5w. Not a fair comparison.
This curve doesn't take into account 0w or 5w and it never cares.
It only needs to know the viscosity at 40c and 100c.
Curve is not "cheating".

#### blingo

The curve is okay around 40°C and around 100°C ;-)
Or for looking at an additional SAE-30 to find north and south.

#### Jetronic

This curve doesn't take into account 0w or 5w and it never cares.
It only needs to know the viscosity at 40c and 100c.
Curve is not "cheating".
You didn't understand what I was trying to say. The viscosity spread at 40C and 100C means the 0W40 has a HIGHER viscosity index, which means LESS viscosity change per degree. This means the 0W40 will thin less above 100C and thicken less below 40C.

You also won't find a 0W oil with a low viscosity index, that's a seperate point.

#### mahanddeem

You didn't understand what I was trying to say. The viscosity spread at 40C and 100C means the 0W40 has a HIGHER viscosity index, which means LESS viscosity change per degree. This means the 0W40 will thin less above 100C and thicken less below 40C.

You also won't find a 0W oil with a low viscosity index, that's a seperate point.

That I agree on. Good points

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