Cold weather gear changes

oilman

AOC Trader
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
 
Not had any issues myself but certainly seems a bit of a minefield!

Will have to check the stuff I have standing by.

What's your thoughts on regular gearbox oil changes? Worth doing at least for Winter then one for Summer?
 
Can you recommend a good gear oil for a nissan pulsar vzr iv changed from a viscous differential to a cusco plate type differential. It will see lots of fast road and trackday driving.

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Not had any issues myself but certainly seems a bit of a minefield!

Will have to check the stuff I have standing by.

What's your thoughts on regular gearbox oil changes? Worth doing at least for Winter then one for Summer?


Hi

No need for changes that often in a gearbox - they don't have the combustion by products to deal with like engine oil has to, so the oil will last longer. Every 3 years or so is fine for a road car.

Cheers

Tim
 
Can you recommend a good gear oil for a nissan pulsar vzr iv changed from a viscous differential to a cusco plate type differential. It will see lots of fast road and trackday driving.

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I think it takes a SAE90LS oil, so the Motul 90PA, Fuchs Race Gear 90LS and Shell TS90 are ideal. If there is any info with the diff that says different, let me know.

http://www.opieoils.co.uk/c-679-sae-90-mtfs-manual-transmission-fluid.aspx

Cheers

Tim
 
Hi,
a local transmission specislist recomends atf for all types of gearboxes. A friend of mine had his fiat box rebuilt and was supplied back to him with atf, possibly dextron 3. Are there any down sides to this and would it be something you recomend ?
My mate has had no trouble so far and says the gear change and drive is much better than before (before his box gave up )

Thanks.
Rob.

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Hi Rob

ATFs are too thin for a lot of gearboxes and will not give sufficient protection, although several things like BMWs use an ATF in certain manuals.

Cheers

Tim
 
I used ATF in my VAG box because although the standard oe stuff is rated as 75w, its actually as thin a water.
 
I think it takes a SAE90LS oil, so the Motul 90PA, Fuchs Race Gear 90LS and Shell TS90 are ideal. If there is any info with the diff that says different, let me know.

http://www.opieoils.co.uk/c-679-sae-90-mtfs-manual-transmission-fluid.aspx

Cheers

Tim

You recommended this OIl for me with similar set up as damo
Fuchs Race gear Oil
And its been by far the best oil iv used in the box ....and Iv used 4-5 Different Oils
Makes the diff feel much better and a bit less clunky then the others
 
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