Cold Weather Gear Changes

[oilman 7]

Hi all,

Around this time of year we get quite a few questions about experiencing difficult gearshifts in cold weather, so we thought you might find this useful.
Using the incorrect viscosity gear oil in your car can make gear changes very difficult when the gearbox, and oil are cold. This is why we often don't recommend using thicker gear oils than the manufacturer specifies. It is easy to think that increasing the viscosity from a 75w-80 to 75w-90 or 75w-90 to 75w-140 isn't going to affect the cold properties of the oil, but it does.
Below are some figures showing the viscosity of a selection of oils at 40C measured in mm²/s ( 1 millimeter²/second = 1 centistoke, A centistoke is a decimal fraction of the CGS unit of kinematic viscosity stokes, which is equal to centimeter per second (cm²/s). 1 stokes is a kinematic viscosity of a fluid with a density of 1 g/cm³ and a dynamic viscosity of 1 poise… In short the thickness of oil!). 40degc may not seem cold but this is the temperature at which the viscosity is measured and is the information you will find on the oil technical data sheets.
I have listed specific brands and products to make it easier to see the differences in viscosity.
Fuchs Sintofluid FE 75w = 40.8 @ 40°c
Fuchs Sintofluid 75w-80 = 49.8 @ 40°c
Fuchs Sintopoid 75w-90 = 90.5 @ 40°c
Fuchs Sintopoid LS 75w140 = 170 @ 40°c

As you can see from that, they are all 75w oils, but there is a large difference in the viscosity at lower temps; the Sintopoid 75w-90 is over twice as thick as the Sintofluid FE 75w when cold and the 75w-140 is almost twice as thick as the 75w-90.

So, if you've got a car that needs one grade of oil as standard, but you've modified it and decide to try a thicker oil, or someone puts the wrong oil in, it might really affect the cold gear shifts. Usually, increasing the quality is a better option than increasing the viscosity when thinking about upgrading from standard fluid.

Also, viscosity ratings are not exact points, but are a band that the viscosity should fall in. The Motul Gear 300 75w-90 has a viscosity of 76.2mm²/s at 40°c and the Castrol Universal 75w-90 is 84.8mm²/s, so you can see there is some variation in oils that appear to be the same viscosity.

A lot of gearboxes specify an 80w-90 rather than a 75w-90, but I would always tend to go for a 75w-90 instead as there can be a large difference is the viscosity when cold. The Motul Gearbox 80w-90 is 164mm²/s, so over twice as thick as their Gear 300 when cold. If you're using an 80w-90 and are having stiff cold gear changes, changing to a 75w-90 is likely to improve things.

If you have any questions or need further advice please post here or email us at sales@opieoils.co.uk

Cheers
Tim.

[petert 586]

Great theory Einstein, but just use a full synthetic such as Castrol Syntrax or Redline Shockproof.

[oilman 7]

It is not a theory, it is all fact. Just to say use Redline Shockproof is daft... Which one, and why? And the viscosity of them at various temps some of the strangest of them all!

 

Cheers

 

Guy

[petert 586]

Sorry, Shockproof Lightweight. Maybe in the Australian climate there's no percivable difference. ie 4-45 deg C. I've used both and I can't tell any difference between a hot day and a cold day.

[Vili 18]

Here in Finland cold day is -30 deg Celsius and at those temperatures gear change becomes almost impossible before gearbox oil heats up on some cars. It's very nice to drive using only the first gear for the first half a kilometer to heat up the box.

But that 500-1000 m is plenty enough to heat up the oil. After that there no such a big difference between cold winter day vs. summer.

Edited January 24, 2013 by Vili

[oilman 7]

Sorry, Shockproof Lightweight. Maybe in the Australian climate there's no percivable difference. ie 4-45 deg C. I've used both and I can't tell any difference between a hot day and a cold day.

 

That's it, you don't really get cold enough for it to be a real issue. In Europe, parts of the US and Canada, parts of Asia etc where it does get properly cold, the gearbox oil viscosity can really affect how the gear changes go from cold. It's also down to the gearbox too - older ones tend not to be so bad, but some newer ones can be really fussy. Like putting a 75w-90 in a post 2000 BMW rather than the standard 75w-80 will lead to real cold shift problems in many cases.

 

Cheers

 

Tim

[Vili 18]

 

That's it, you don't really get cold enough for it to be a real issue. In Europe, parts of the US and Canada, parts of Asia etc where it does get properly cold, the gearbox oil viscosity can really affect how the gear changes go from cold. It's also down to the gearbox too - older ones tend not to be so bad, but some newer ones can be really fussy. Like putting a 75w-90 in a post 2000 BMW rather than the standard 75w-80 will lead to real cold shift problems in many cases.

 

Cheers

 

Tim

 

My BMW doesn't like shifting in cold even with the std. gearbox oil. But still it's not half as bad as Audi or other small engined VAG-cars.

[oilman 7]

Hi

 

A lot of people put a 75w-90 in VAGs, when a lot of them want a 75w or 75w-80.

 

Which BMW have you got? An E46 by any chance? They are the worst ones for cold gear changes. Using a mix of MTF and ATF often sorts the problem out.

 

Cheers

Tim