Penrite Synthetic Gearbox Oil

GR124 · Postby **GR124** » Sun Oct 07, 2018 12:19 am

RS2000 wrote:GR, its 1999 NB8A which is the same as 2000.

Big thanks mate, I’ll run with the GL-5

JBT wrote:Nulon do a GL4 synthetic. I'm using that in the NC and it's fine.

Cheers JBT, this issue was the Penrite full synthetic oil I have purchased is GL-5. Looks like it will be fine.

Red_Bullet · Postby **Red_Bullet** » Sun Oct 07, 2018 12:36 pm

Most of everything I've read recommend a GL4. Which is what I use, never tried a GL5 in it. Something to do with compatibility with synchro rings.

RS2000 · Postby **RS2000** » Sun Oct 07, 2018 6:18 pm

I see that Penrite now have a full synth GL4 75W-90

https://www.penriteoil.com.au/applications/car-4wd/gear-oils/pro-gear-gl-4-75w-90

Magpie · Postby **Magpie** » Sun Oct 07, 2018 6:25 pm

https://www.widman.biz/uploads/Transaxle_oil.pdf

Wombit · Postby **Wombit** » Sun Oct 07, 2018 8:03 pm

Magpie wrote:https://www.widman.biz/uploads/Transaxle_oil.pdf

Hey Magpie, what's your reason for posting this article?

Funnily enough, I came across this earlier today when looking into GL-4 and GL-5 oils, and am going to order the Penrite GL-4 oil tomorrow.

I'll be getting the full suite of fluids that I haven't yet changed recently, including diff, power steering, and brake fluid.

Magpie · Postby **Magpie** » Sun Oct 07, 2018 8:25 pm

Was because people were asking the difference

Wombit · Postby **Wombit** » Sun Oct 07, 2018 8:49 pm

Cheers for that, that's what I thought.

The key point I took away from it was there's a higher level of sulphur/phosphorus additive in the GL-5, which disagrees with the bronze synchros in the 6-speed transmission, causing excessive wear.

RS2000 · Postby **RS2000** » Sun Oct 07, 2018 9:00 pm

I'd be interested to know if the NB8A owners manual lists GL5 as suitable for the gearbox, like the Mazda workshop manual does?

manga_blue · Postby **manga_blue** » Sun Oct 07, 2018 9:58 pm

My NA8 owners manual says both GL-4 and GL-5 oils are OK and, apart from a few changes to the turret and shift forks, it's the same 5 speed gearbox as the NB8A.

manga_blue · Postby **manga_blue** » Sun Oct 07, 2018 10:20 pm

manga_blue wrote:My NA8 owners manual says both GL-4 and GL-5 oils are OK and, apart from a few changes to the turret and shift forks, it's the same 5 speed gearbox as the NB8A.

Just found the page for the NB8A Owners Manual. It says the same thing: GL-4 and GL-5 are both ok. 75W-90

https://manuals.co/workshop/mazda/mx-5/2000-mazda-mx5-owners-manual/3275/252

RS2000 · Postby **RS2000** » Mon Oct 08, 2018 7:35 am

Many thanks for that manga.
So, there is a bit of contradiction at the bottom of page 5 in the article https://www.widman.biz/uploads/Transaxle_oil.pdf
He says follow the manual (for modern cars), then says GL5 is not suitable for synchro transmissions.

GR124 · Postby **GR124** » Mon Oct 08, 2018 8:33 am

Magpie wrote:https://www.widman.biz/uploads/Transaxle_oil.pdf

Magpie I also found that write up as well during my google search.

I found this from Penrite as well https://www.penriteoil.com.au/assets/pd ... ential.pdf

I have already cracked open the bottle of Full Synthetic GL-5 so I'll be using it.

Red_Bullet · Postby **Red_Bullet** » Mon Oct 08, 2018 9:16 am

I think from memory it depends on what the synchro rings are made from. While GL5 or GL4 may both "work" I believe from what I have read that GL4 is preferable. When I got Automotive Plus to replace a broken gearbox for me they put martini extreme pressure 75/80 GL4 in it.

I have a 6 speed waiting for the next failure of the 5 speed and have some of the Motorcraft GL4 waiting ready to go in it.

GR124 · Postby **GR124** » Mon Oct 08, 2018 9:29 am

If I get a minute today I'll give Penrite a call. I'm guessing they wont have a hang over after the Bathurst result :roll:

Magpie · Postby **Magpie** » Mon Oct 08, 2018 10:41 am

My concern is the cost of repair to the 6 speed box. Hence I will continue to run a GL-4 oil.

A second hand (unopened, unknown condition) costs over $1k (less than a hardtop at the moment) the OEM parts are VERY VERY EXPENSIVE and as Daffy found out the main shaft is made on demand...

Yes the Aisin 6 speed is used in other cars, but interchangeability information is very hard to come by