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GL5 gearbox oil

Red Devil

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Ok, so I'm new to gt6 ownership so I'm slowly working many way through service related items so that I know where I stand with things. I have a mk2 although for the point below it probably doesn't matter. A couple of weeks ago I had the gearbox tunnel off to replace the gearstick bushing. At the same time I emptied and refilled the gearbox oil and also topped up the rear diff.


Today I reached for the oil as I was going to oil the trunnions. Well I couldn't help but notice that what I have been sold is 80/90 but is GL5 a I'm sure everything I have seen says it should be GL4. Do I need to drop it our again and replace?


I'm so annoyed about this if I have to replace it as not only is it time and cost but I got it over the counter at rimmers and they knew it was for a gt6 as they even gave me a copy of the catalogue! It is comma 80/90 gl5.


Advice please!





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There, s lots of debate over gl4 gl5 options


more modern gl5 doesnt read as detrimental as some years back, the difference is GL5 can errode bronze based metals when used in hot and high load operations


so the basic advise would be tomdrain and refill with GL4


many have used 5 without problems , my own experience was with truck warranty when some clever dick

decided to save costs by making gl5 the std. Was not long before the diff planet gears lost the thrust

washers and proved a very expensive cost saving


so my view is dont panic but change it soon.



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The GL4 versus GL5 argument is long and complicated.


As to whether GL5 is OK or not depends on the manufacturers blending chemistry - and they are all different.


GL5 oils where the chemistry includes a significant quantity of sulphur (not all of them do) makes the oil "yellow metal" corrosive under certain conditions.


The Yellow metal corrosion properties of sulphur rich GL5 is ONLY activated when the oil is VERY hot and been subjected to significant SHEAR activity.

These conditions are ONLY achieved when using the oil in a Differential, not a gearbox.

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