Changing Transmission Oil

[MNBoxster]

Originally Posted by JackG

Redline MT-90 is a GL-4 rated 75W90 synthetic gear lube.

Royal Purple also has a Max-Gear synthetic that is GL-4/5 rated.

Both are claimed to not be corrosive to soft metals. Maybe these are possibilities?

Hi,

They certainly could be. I have heard nothing but good things about the Royal Purple Line of products, and I use RedLine MT-90 in my Lotus Esprit.

The Lotus uses a Citroen SM Gearbox (modified), and it's really at the extreme of it's HP Rating in the Esprit. It uses Brass Synchros and so a GL-4 is called for. The Tranny shifts smoother and it is a must for any power-modded Esprit. In fact, Lotus introduced the Esprit SE because the Citroen Gearbox was no longer available and so they switched to a Renault Box which could take more HP, so Lotus redesigned the Head and aded a Chargecooler to up the HP to match the new Box.

If the Boxster uses hard metal synchros, there's no problem at all, but I've never been inside one and so cannot say for sure. But, GL-5 has been reported repeatedly to have attacked soft metal parts. GL-4 does not.

One other thing about the Synthetics is that they invariably make the Tranny noisier. This is because of their lower viscosity, and for some people, this may be a consideration.

I love synthetics, but not necessarily in every application. If the benefits cannot be utilized, it seems silly (to me at least) to pay a premium for the stuff. So long as the Oil level is kept at spec, a gearbox rarely fails because of the Oil it's using, except when Hypoid Lubes are used. Otherwise, most Lubes out there are really adequate. Gearboxes fail mostly because of consistent Operator Error...

Happy Motoring!... Jim'99
Happy Motoring!... Jim'99

[Cloudsurfer]

Resurecting an old thread here.... For a Boxster S 6-speed.... Is MT-90 a good choice? What else is worth considering? I'd prefer to stay with a synthetic due to the occasional use in the winter.

Patrick

[MNBoxster]

Originally Posted by bmwm750

Resurecting an old thread here.... For a Boxster S 6-speed.... Is MT-90 a good choice? What else is worth considering? I'd prefer to stay with a synthetic due to the occasional use in the winter.

Patrick

Hi,

You are not going to go wrong with RedLine MT-90. I've been using it for years in my Esprit, 240Z and my Race Car. It's really good stuff and you'll probably report better, more positive shifting and quieter operation. Obviously, this would be my choice...

Happy Motoring!... Jim'99

[John V]

I have had very good results with MT-90 over the years as well. However the Redline folks suggested to me that the best match for the Boxster S transaxle was their 75W90NS (non-slip) oil. I've had it in for about a year with no complaints. Some people, especially owners with B+M shifters, prefer the Redline "cocktail" which mixes the 75W90NS and Light Gear oil.

[Cloudsurfer]

Well, the MT-90 is a GL-4 fluid, while the 75W90 is a GL-5. The question then, obviously, is does the 6-speed box in the S have any yellow metal in it to worry about?

Patrick

[CJ_Boxster]

Dont forget you have to remove the metal rock sheild under the tranny and you will need a Pry bar to get the diagonal braces and rock shield to pop off.

[roadracer311]

Speaking of pry bars... Has anyone had trouble getting the plate and braces to line up when going back on?

[saaber]

Originally Posted by MNBoxster

Hi,

They certainly could be. I have heard nothing but good things about the Royal Purple Line of products, and I use RedLine MT-90 in my Lotus Esprit.

The Lotus uses a Citroen SM Gearbox (modified), and it's really at the extreme of it's HP Rating in the Esprit. It uses Brass Synchros and so a GL-4 is called for. The Tranny shifts smoother and it is a must for any power-modded Esprit. In fact, Lotus introduced the Esprit SE because the Citroen Gearbox was no longer available and so they switched to a Renault Box which could take more HP, so Lotus redesigned the Head and aded a Chargecooler to up the HP to match the new Box.

If the Boxster uses hard metal synchros, there's no problem at all, but I've never been inside one and so cannot say for sure. But, GL-5 has been reported repeatedly to have attacked soft metal parts. GL-4 does not.

One other thing about the Synthetics is that they invariably make the Tranny noisier. This is because of their lower viscosity, and for some people, this may be a consideration.

I love synthetics, but not necessarily in every application. If the benefits cannot be utilized, it seems silly (to me at least) to pay a premium for the stuff. So long as the Oil level is kept at spec, a gearbox rarely fails because of the Oil it's using, except when Hypoid Lubes are used. Otherwise, most Lubes out there are really adequate. Gearboxes fail mostly because of consistent Operator Error...

Happy Motoring!... Jim'99
Happy Motoring!... Jim'99

This has probably been answered elsewhere but if someone is searching this may help... In regards to GL4/GL5 and is their Yellow metal in there Qs, I got some good info From Doug H. at Renntech re original tranny oil FYI. This was in regards to an 00' S

"...perhaps the initial fill was an Esso product
Mobil are emphatic about specifying their "PTX" lubricant or going to a Dealer and Castrol (Germany) recommend their excellent SAF-XO (at 160k kms OCI)

In any case they all concur on a 75w-90 synthetic (GL5) but not all gear oils are made the same and the above two are recommended with good purpose and no doubt to improve shift quality and longevity

Many Manufacturers do have special gear oil "brews" and in many cases these are only available via the Approved Dealers"

Also, if you don't want to go through all the hassle of removing the plates underneath, you can use a $6 hand pump and pump out the old fluid via the fill hole. On the 00' S the fill hole is on the drivers side and is a 10mm. You don't have to remove anything this way but you will only get about 1.75 liters out, leaving about 1/2 liter of the old stuff, so it is great for refreshing but probably doesn't replace the 90k recommended drain and fill.

[HammerESQ]

Bumping this thread again... Is the gear oil capacity, and filling instructions the same for the 6 Speed in the Boxster S, and the 5 speed in the regular Boxster?

Thanks,
Eric