Manual or automatic oil?

Good day everyone, it’s recently come to my attention that for those numerous owners who suffer the ‘notchy gearbox’ syndrome (that’s most of us), it can ofttimes be resolved by changing out the gearbox oil for automatic transmission fluid. With the proviso that it must be changed every 30,000 miles. But does anyone recommend what oil to use, answers on a postcard?

That’s a first for me, can’t say anyone on here has mentioned it before.
As for what I use, Castrol Syntrans 75w 90.

Yup, new to me as well. Came across it talking to my son who was putting it in his bmw, Redline even offer it as an alternative on their website, so it can’t be complete hokum.

Mt 90 Redline I’ve heard of being used. Being as I’m a tight one it’s a bit pricey so stuck with the Castrol.

I tried it in my NA once, the gearbox was noticeably noisy at idle when hot. I didn’t leave it in there for very long.

Mercedes used to use it in the 80’s - 90’s in manual transmissions but I would rather use one of the readily available and more modern spec GL-4 oils as Mazda intended.

If you have a NA or NB the gearbox oil needs to be GL-4, do not be tempted to go for GL-5 as it is “better” it is too slippery for the syncronisation to work peoperly and it will be harder to change gear.

Ok… And following that thread they say gl-5 has additives that can corrode the metals used in the synchro mesh! So my redline manual gear oil isn’t to bad.

The GL-5 is not suitable for the NA and NB gearbox because of the lack of friction in the syncromesh, which is needed for a smooth gear change. The fact that it damages the syncro rings metal (phos-bronze) is a problem that comes later on.

Yup! I emailed Redline and the guy confirmed it, Redline GL-4 is what they recommend fit the mk1’s, and as I’ve got Redline in already we’ll stick with that, any slight cold running notchiness I’m now calling ‘character’. That’ll do me.