Best gearbox oil?

Afternoon all,

I’m wondering if anyone can give me a any recommendations from experience about which is the best gearbox oil to really complement the 5 speed box in a MK3 NC…

I’m torn between these two:

https://www.opieoils.co.uk/p-739-castrol-syntrans-multivehicle-75w-90-fully-synthetic-car-gearbox-oil.aspx

https://www.opieoils.co.uk/p-1020-red-line-synthetic-manual-transmission-90-mt90-75w-90-gl4.aspx

Of course, I’m open to any recommendations deviating from the above!

What to people have the best results with?

Similarly, I’m going to put this in the differential… Can anyone advise otherwise?

https://www.opieoils.co.uk/p-806-mobil-mobilube-1-shc-75w-90-fully-synthetic-performance-gearbox-oil.aspx

Thanks :slight_smile:

Syntrans probably easier shifting cold
Redline maybe not so easy to shift but potentially slightly better at higher level of abuse.

SHC Gl-5 fine for diff.
IMHO

I said this in my two posts in this thread re the Redline, it mentions the Syntrans and which diff oil I used.

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Buuuuutttt…

You’ve got the 6 speed box which are famous for being notchy and a hot awkward, particularly when cold…

The change on mine is really quite nice so I just want to change it for the piece of mind more than anything, but at the same time I’ve changed transmission oils in the past and had some unexpected problems with it, namely the oil completely changing the shift dynamics despite being the correct oil…

This is why I really want to know what other people are using and are happy with. The car doesn’t get abused/driven hard and is only used at weekends, so I want which ever oil will give the best quality gear change.

As I say, I can’t really decide between Syntrans or redline at this point

The Syntrans is suitable for the 5 speed even though that doesn’t display the 1st to 2nd notchy change. I’ve used it in my Mk1 5 speed, all good.
As long as it says GL4 on the label it’s good.

As they say here, suits all model although Mobil it’s GL4 spec.

https://www.mx5parts.co.uk/gearbox-manual-fully-synthetic-models-p-1591.html

Funnily enough, there’s one review of that oil on the mx5 parts website and someone is complaining of a stiff change when cold, citing the GL5 standard vs recommended GL4 standard as being the culprit

Having said that, my user manual specifies either GL4 or GL5… Do you know what the difference is between them? Is GL a durability or viscosity indicator?

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Explanation here…

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You are probably over thinking this. For a box that you say has no shifting issues the safe bet is somethinglike syntrans with GL-4 spec. GL-5 oils generally have an extreme pressure additive package based on Sulphur compounds which are thought to cause damage to brass components.

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Just an opinion, but it’s best to ask what is the “Correct Oil”.
To which (as already pointed out) are many.
As long as you choose the “Correct Oil” you should have no problems.
Brand is generally a personal preference.
I recently have used Total, but that’s just me.
If opie oils comply and is your preference then job done. :+1:
I use the Total both in the gearbox and diff.

Can’t remember exactly when, but they modified the gearbox too so it shifted easily without bulking. In particular, when cold. So not all NC"s suffer the gearbox bulking problems. (Another story).
EDIT- My gearbox is NOT “notchy”.

An email sent and received as below.

My email to Total Oils.

Hi l have a Mazda MX5 2.0 2013.
I have just changed the 6 speed transmission oil based on your
recommendation. i.e Dual 9 FE 75W90. I have been told I should
only use a GL4 oil due to the additional chemicals used for a GL5
oil which can harm the synchromesh hubs etc. But as you list
suitable for both GL4/5 I am now very confused! Is it safe to
use? Many thanks.

From Bob WOOD at Total Oils.

Technologies have changed but the performance levels have stayed the same. In some of the GL5 oils they contain twice as much EP Sulphur Phosphorus additives as a GL4 and this can affect copper in synchromesh. Using the new technology in Transmission Dual 9 FE 75W/90, different chemistry has been used to get both performance levels without affecting the synchromesh yellow metals.
I hope this explains everything.
Best regards,
Bob

That’s a bit confusing, buyer claims they supplied GL5 but the blurb on actual stuff they are selling is GL4. Changes could have been made though.

All I’ll say is GL4 75w 90 will be ok whatever the brand. I’ve lost count how much I’ve bought and used in MX-5’s. I’m a regular oil changer, done it also for a couple of members cars too, 5 speed, 6 speed, Mk3, Mk2 and Mk1. The Syntrans isn’t a miracle cure for the notchy 6 speed but it helps ease the change, 5 speed I would’ve have picked one if they did one for the sport model, all 6’s.:+1:

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That’s a good tip and advice too! :+1:

Right that settles it then, syntrans it is!

Should be doing it next weekend so I’ll report back with my findings.

Made sure that I can get all drain and refill plugs off the diff and box today too, everything is moving nice and freely :ok_hand:

Do you have the new crush washers as well?
Necessary, because re-used ones usually leak!

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No I don’t!

Where can I get them?

eBay is a good source.
Bit limited at present dealer wise.
Just type in MX5 NC gearbox drain plug washers. Various come up.
2 each for diff and gearbox.
Do sets, i.e 4 and an engine drain plug washer too.:+1:

5 speed no washer on the fill plug, wrap with PTFE tape to seal the thread on the plug.:+1:

Ahh, thanks for that :+1:

Oh that makes life easier definitely… I’ll just have to raid the garage for it!

I’ve reused sealing washers more times than I’ve replaced them over the years… Never had a problem! Though I do always check them to make sure they’re not over compressed!

I must say, I gave the fill plug a close inspection today when I attempted to make sure it will move and there’s no sign of any ptfe tape on it at all… Is sealing this way standard practice from the factory?

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TBH I don’t think it’s really needed but I do it, think it has a slight taper on it. The last one I took out didn’t have anything on it and that was untouched from the factory. Don’t over tighten it.

Same here re crush washers, I’ve reused them when I haven’t got that size, if they aren’t too crushed or out of shape