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Cold weather gear changes

Discussion in 'A4/S4 forum(B5 Chassis)' started by oilman, Jan 21, 2013.

  1. oilman
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    oilman Member

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    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.
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  2. dan_s2k
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    dan_s2k New Member

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    Hi,

    Please could you confirm the correct oil for my 2003 1.9 TDi 130 5 speed and how many litres I will require? I've read on here there is a difference between the 5 speed and 6 speed, is this right? As I can't see this as an option on your website?

    Also, any recomendation on brake fluid and how many litres required for a flush?

    Thanks,
    Dan.
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  3. oilman
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    oilman Member

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    Hi Dan

    What's it like with cold shifts?

    Cheers

    Tim
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  4. martin_addlestone
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    martin_addlestone Member

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    Hi Tim - do you do an equivalent to the Redline MTL oil - I have been told that the one I should be buying for my Merc with a crunchy 6 speed when cold but it's pretty pricey for 2 litres
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  5. oilman
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    oilman Member

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    Hi

    If you have a problem with a gearbox, Redline is something I'd always recommend. You can try something cheaper, like the Motul Motylgear, but it's less likely to sort the problem out. Considering the difference over 2L is about a tenner and it will stay in the gearbox for a couple of years at least, so I'd say the difference is worth it.

    75w-80 / 75w-85 MTF's - Manual Transmission Fluid

    Cheers

    Tim
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  6. dan_s2k
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    dan_s2k New Member

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    Not good, its on 170k and wouldn't surprise me if the oil hasn't been changed to date so definitely due! Its not too bad when warm but very notchy when cold.

    Dan.
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  7. oilman
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    oilman Member

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    Hi Dan

    The standard spec is a 75w-90, but as it's not good when cold, going for a good 70w-80, 75w-80 or 75w-85 like Redline MTL, Fuchs Sintofluid, Amsoil MTF or Redline MT85 can really help things.

    75w-80 / 75w-85 MTF's - Manual Transmission Fluid

    Although they are thinner than the standard stuff, they are very high quality and will give plenty of protection.

    Cheers

    Tim
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  8. Bradderz_1988
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    Bradderz_1988 Dont replace it, Upgrade it !!

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    My gearbox has a very crunchy 1st and 2nd gear from cold and is better when warm it also has a whine from the box when in 2nd i no why this is as i was giving it some welly and slightly missed the gear which resulted in the cruch/grating noise i may just source a 2nd hand box i have done a few gearbox strips on a few peugeots and citroens at work but for the price off a 1st/2nd syncro and the time involved to change it i see it more off an easy option to just throw a box in but then theres always the risk of not knowing the condition of the box i would recieve is there a write up on changing the syncro on the 01A box and anyone have a price on the syncro i need to way up my options ???
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  9. dan_s2k
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    dan_s2k New Member

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    Thanks Tim. Could you also advise on quantity required for gear oil and brake fluid changes?

    Dan.
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  10. oilman
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    oilman Member

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    Hi Dan

    You'll need 3 bottles of gear oil (my data varies from 2.3-2.8L, I assume that's the 5 or 6 speed versions). The brakes take about a litre of fluid, but I don't have any accurate brake capacity data.

    Cheers

    Tim
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