Noob question - Which gearbox oil?

[RileyR]

I know this has been covered on a few different forums and I have been reading for over an hour now, but all it has done is confuse things further

And I know that I am probably opening a can of worms here.... but here gores anyway...

I am wanting to change my gearbox oil in my 1996 NA8 (5speed manual) to a high quality product - for street and track use

Redline MT90 gets both great and horrible wraps - but is GL-4
Nulon full synth 75w-90 is said to be good, but is GL-5 which some say will damage the gearbox.

Some say to only use GL-4 (and avoid GL-5 because it damages our gearbox), some say it doesnt matter, some say that GL-5 offers better protection :/

All the info I have come across seems very contradictory and confusing. - Im hoping to do the change this weekend...

Also, I just use whatever I put into the gearbox into the shifter turret?

Any advice would be greatly appreciated

[hks_kansei]

Mazda recommend GL4 from memory, but have a read of the booklet, it tells you.

I've always used Castrol VMX-M for both the gearbox, and the diff, including my Torsen (clutch based diffs use a different oil, and Torsen T1 need one rated for high shear pressures)


For the Turret, it's supposed to be greased, not oiled. Over time though the seals that separate the turret from the box wear and the two mix. Many people put some of the regular gearbox oil in there, but I just use a glob of bearing grease.




Everybody has different preferences though, same as engine oil, so what you'll get is about 50 replies each one suggesting something different, and at the end of it you'll still be sitting where you are now thinking "so which one should I use?"


For reference, VMX-M is about $45 a bottle, one bottle will do your gearbox, AND diff, and still have a litre to spare.

[hks_kansei]

As for the some oils/products offering more protection thing, it amy be correct, but if the item you're trying to protect isn't designed for it you can just make things worse.


Saltwater in a fishtank will reduce the likelihood of algae as opposed to using freshwater.
Therefore, Saltwater offers more protection.

However, if you're keeping goldfish, you may end up with an algae free fishtank.... with dead fish.



You'll need to look it up, but basically the thing that usually gets annoyed in gearboxes (with the wrong oil additives) is the synchros.
Driving a box with stuffed sychros isn't that fun.

[RileyR]

ah ok, well that clears up the turret issue, thanks.
I had a look in the owner manual but I can find any recommendations for manual gearbox oil - only auto's
My diff oil was replaced when I had a t2 put in a few weeks ago, so its good to go

[RileyR]

yeah I definitely want the right oil for my gearbox. I have read that GL5 will ruin synchros - hence my hesitation to go for Nulon oil. But ive also read that it wont hurt the synchros and that GL5 is better as it offers more protection to the gearbox

[hks_kansei]

My gearbox is happily going on 170,000km
My GF's NA6 box is on about 450,000km

Both using regular old Castrol oil, GL4, just changed at the regular intervals, sometimes earlier.

Both boxes healthy and good, mine just has a slight whine in 2nd (on decel loads) from me driving it a bit too hard in motorkhanas.

[TrackAttack]

For the Turret, it's supposed to be greased, not oiled. Over time though the seals that separate the turret from the box wear and the two mix. Many people put some of the regular gearbox oil in there, but I just use a glob of bearing grease.

As per the workshop manual, the change control case takes 80-95cc of GL-4 or GL-5 (75W-90)

[Mr Morlock]

the spec for the oil in your gearbox or any fluids will definitely be in the owners manual- all makers include this info in the Owners manuals. If you buy oil from a proper oil distributor you can get advice on what to use- I am fortunate in having a business close to me that sells oils. The quickest way to wear synchros is abuse a gearbox. The other thing to do is ring one or more of the Oil companies info lines and they will give advice. HKS has covered it very well.

[93_Clubman]

NA8 Owner's Manual specifies GL4 or GL5 GB oils.
NA Factory Workshop Manual specifies the same GB oils for the turret:

MX5 GB 5 speed turret oil1.JPG

[RS2000]

If the manufacturer says use GL4 or GL5 then they both must be ok.
If they only mention GL4, then I wouldn't use GL5.
See 'Gear & Synchro Wear protection' on 2nd page of:

http://www.redlineoil.com/content/files ... 20Info.pdf

Cheers

[93_Clubman]

Oil specs source: Mazda NA8 Technical Specs:
viewtopic.php?f=29&t=63728&p=795615&hilit=na8%2520gearbox%2520oil%2520spec#p795615

PRR clarifies ref GL5:
viewtopic.php?f=29&t=58558&p=737913&hilit=gl5#p737913

[RileyR]

Thanks for all the info every one. I will order myself some redline mt90 tomorrow (i cant find a local seller) -the good reviews far outweigh the bad by the looks of it. Ill post up what I think of it when I get it done

1996 BRG NA8