Gearbox Oils - Castrol vs Redline?

booki89 · Postby **booki89** » Wed May 28, 2014 1:53 am

Hey all,

Been doing some heavy reading from past forums and struggling to make a decision.

A buddy bought 2 bottles of Syntrans 75w-85 for his 98 NB, but after we did some reading...we are now tempted to use Redline MT90 instead...

I am currently using Castrol Syntrans 75w-85 in my car at the moment (NA8), cold start, gear change from 1st to 2nd is a bit stiff, no clunks or bad noises just a little hard to get in. After that first change its fine, no complaints.

Do you think its worth swapping the oil before we open it to get some redline MT90?

tescoking · Postby **tescoking** » Wed May 28, 2014 4:02 am

Redline MT90

booki89 · Postby **booki89** » Wed May 28, 2014 10:15 am

Have you tried any other oils?
Can you justify tour answer a little.

93_Clubman · Postby **93_Clubman** » Wed May 28, 2014 11:48 am

Redline is very well regarded, but forumites have also had very good results using Nulon full synthetic 75W-90:
http://www.nulon.com.au/products/Gear_a ... a_kZ5w2X_g

to which they add Nulon G70 additive:
http://www.nulon.com.au/products/Specia ... Treatment/

Plenty of posts regarding the Nulon GB oil & additive on here.

booki89 · Postby **booki89** » Wed May 28, 2014 12:01 pm

I thought the general consensus was to use gl4 not gl5?

Because gl5 causes accelerated wear due to the brass components?

16bit · Postby **16bit** » Wed May 28, 2014 12:38 pm

having just had castrol in and now redline i would say redline is superior for feel.

much smoother from cold.

as for protection i can't comment.

93_Clubman · Postby **93_Clubman** » Wed May 28, 2014 1:26 pm

booki89 wrote:I thought the general consensus was to use gl4 not gl5?
Because gl5 causes accelerated wear due to the brass components?

NA8 Owners Manual says GL4 or GL5 for manual transmission.
Don't forget PRR's input:

project.r.racing wrote:Go to the specs of any bottle or oil manufacturers website and have a look at the specs. If it is GL-5 and also has something like MIL-XXXXXXXXD or E in the specs. It is fine to use on brass synchos as it has additives to protect the brass.

project.r.racing wrote:
project.r.racing wrote:Again GL-5 is fine as long as it has a military spec attached.
MX5 gearboxes are not the only Mazda gearboxes with brass synchos built in the 90s and early 00s. All this has been tried and tested and proven before.

This is what I use:-
http://www.penriteoil.com.au/products.p ... oducts=376
for my 323 with transaxle gearbox and hypoid clutch plate lsd. and have so for 100,000km. it's a GL-5 75-90.

manga_blue · Postby **manga_blue** » Wed May 28, 2014 1:27 pm

Mazda specify either GL-4 or GL-5.

Source: Mazda NA8 Technical Specs

Personally I've tried a lot of different gear oils. Nothing that's readily available has come close to Redline MT-90. Some others have been disasters. I haven't tried the Penrite gear oil yet but so far I've had a a lot of success with all their other oils.

JBT · Postby **JBT** » Wed May 28, 2014 6:53 pm

project.r.racing wrote:Again GL-5 is fine as long as it has a military spec attached.
MX5 gearboxes are not the only Mazda gearboxes with brass synchos built in the 90s and early 00s. All this has been tried and tested and proven before.
This is what I use:-
http://www.penriteoil.com.au/products.p ... oducts=376
for my 323 with transaxle gearbox and hypoid clutch plate lsd. and have so for 100,000km. it's a GL-5 75-90.

Penrite here too but Transgear 75W-90. Used in our old 2002 Astina that my daughter now has and the MX-5. Purrrfect.

Locutus · Postby **Locutus** » Wed May 28, 2014 8:57 pm

16bit wrote:having just had castrol in and now redline i would say redline is superior for feel.

much smoother from cold.

as for protection i can't comment.

this.

booki89 · Postby **booki89** » Wed May 28, 2014 9:12 pm

Went with the Redline MT-90.

Will post up how it goes after I change it and take it for a drive

hks_kansei · Postby **hks_kansei** » Wed May 28, 2014 10:21 pm

Castrol VMX-M

One bottle does gearbox and diff.

corners · Postby **corners** » Thu May 29, 2014 10:05 am

I haven't used MT90 but I have used the Lightweight in a 6 speed. It does improve the feel but I'm not convinced its any better than any other gear oil.

I'm not using the Nulon stuff with the additive and it feels good

Sailor · Postby **Sailor** » Thu May 29, 2014 4:27 pm

+1 for the Castrol VMX-M works a treat in my NC which are notorious for hard shifting when cold.

MrRevhead · Postby **MrRevhead** » Thu May 29, 2014 7:42 pm

I use VMX 80. Was great when first changed, now, 4000kms later, it's a bit notchy shifting into 2nd (new upper, lower boot & nylon bushing installed at the same time).

I will add G70 soon and hope it smooths things out.

It's great that a 4L bottle does both diff & gearbox with some to spare.