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Old 06-20-2022, 02:16 PM   #1
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Transmission fluid for 986 5 speed - redline?

After reading the Pelican parts/101 projects article on Boxster transmission oil changes, it sounded like any 75w90 gear oil would work in the Boxster 5 speed, so I went ahead and purchased some Redline MT-90, and put it in.

I don't know what gear oil was in there before, but the transmission shifts much smoother now, it slides right into gear.

However, after putting it in I noticed that Redline states on their website not to use MT-90 in hypoid differential applications, and the boxster 5-speed indeed has a hypoid differential. So I became concerned that this oil would wear out the diff gears.

Now, some more searching on this forum reveals that the Boxster 5 speed is really just an Audi 012 transmission, e.g. as you would find on a 2003 Audi A4 FWD 5 speed (and many other FWD Audi models).

It appears MT-90 is in fact the recommended Redline oil for the Audi 012 transmission equipped cars... and many people on the Audi forums use it, with no apparent problems or damage. Moreover, Redline MT-90 is rated to the VW/Audi G 052 911 spec, which is what the 012 transmission requires.

So right now I am thinking that this oil probably is a proper and safe oil for the Porsche 986 5 speed despite the fact that it has hypoid gears.

As a side note, when changing my oil I noticed that the transmission was previously way overfilled- it poured out of the fill hole instead of being 11mm below the line. Some comments on this forum suggest that this can cause the transmission to leak onto the clutch, and cause it to slip. I did this whole project because of a mysteriously slipping clutch, despite the clutch being fairly new. The slipping clutch didn't look worn down, but after replacing everything with the "complete" Pelican Parts kit and changing the fluid, the new clutch doesn't slip like the old one did.

Finally, I contacted Redline asking if I should drain this oil back out, and they said no, if starting from new it's not the oil they would recommend, but they said it should work fine.

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Old 06-24-2022, 07:05 PM   #2
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You are correct that this transmission is the 012, but if you search through the forums you will find a fair number of people who have had bad experiences with mt90. If it's not recommended for hypoid gears, it shouldn't be used with hypoid gears.

Btw, the original audi factory recommended transmission oil was also a special one off, just like the porsche oil.


It's your transmission, and I'm not gonna tell you to drain it, but does that guy's logic sound right to you?

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Old 06-26-2022, 07:42 AM   #3
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You are correct that this transmission is the 012, but if you search through the forums you will find a fair number of people who have had bad experiences with mt90.
I did search as much as I could, and most people seemed to be having no problem with it. I noticed one person complaining of 'notchy' shifting, but my shifting is extremely smooth feeling.

Indeed, the logic from the redline engineer makes sense to me. Here is the full text of what they sent:

Quote:
Thank you for contacting Red Line Oil, in your Boxster transaxle the 75W90NS would be recommended as the Porsche hypoid amnual transmission fluid is called for. These transaxles don’t have a high offset hypoid gear set so don’t technically require a GL-5 gear oil but that is what they call for. The MT-90 would almost provide GL-5 protection level, would be suitable but just a little different product than called for and recommended.
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Old 06-26-2022, 08:14 AM   #4
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Originally Posted by casioqv View Post
I did search as much as I could, and most people seemed to be having no problem with it. I noticed one person complaining of 'notchy' shifting, but my shifting is extremely smooth feeling.

Indeed, the logic from the redline engineer makes sense to me. Here is the full text of what they sent:
Just to put his comment in context, the fluid which is made for Porsche does not have a GL rating of any kind; a small division of Royal Dutch Shell (Burhma) makes it to Porsche specs, so it completely unique.

For years, many aftermarket gear oil companies have claimed to have substitute products, but in reality, do not. Years ago, we contacted Mobil, Castrol, and several other oil company's technical groups, and the honest ones responded that the Porsche product is a "one off", and that they had no matching products.
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Old 06-26-2022, 04:59 PM   #5
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I have tried the cocktail and snake oils of transmission fluid in both my 996 and 986S. All have had their quirks. Having said that, the one sold by Porsche is the one that has worked best for me and I personally swear by it. Your mileage may vary.

I have never had great experiences with Redline MT-90 in a street application. Takes it a while to heat up to really work but some folks out there worship it.
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Old 06-26-2022, 07:38 PM   #6
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Originally Posted by JFP in PA View Post
Just to put his comment in context, the fluid which is made for Porsche does not have a GL rating of any kind; a small division of Royal Dutch Shell (Burhma) makes it to Porsche specs, so it completely unique.
Any idea why Porsche would use such a custom fluid when they're just using a VW/Audi transmission that itself has a spec (VW/Audi G 052 911) that is widely matched by a lot of products?

I'd imagine maybe they are trying to tune the 'feel' of the transmission engagement for performance driving in a way VW wouldn't care about?

Still, it makes me doubt that using a VW/Audi spec oil will cause premature transmission failure.

Honestly, I didn't know all of this when I bought the MT-90. Likely I will change back to the Porsche fluid if I change it again, but in the mean time there are much more pressing maintenance issues on this 22 year old car... and I am satisfied that the MT-90 isn't likely to cause transmission failure.
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Old 06-27-2022, 03:09 AM   #7
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Quote:
Originally Posted by casioqv View Post
Any idea why Porsche would use such a custom fluid when they're just using a VW/Audi transmission that itself has a spec (VW/Audi G 052 911) that is widely matched by a lot of products?

I'd imagine maybe they are trying to tune the 'feel' of the transmission engagement for performance driving in a way VW wouldn't care about?

Still, it makes me doubt that using a VW/Audi spec oil will cause premature transmission failure.

Honestly, I didn't know all of this when I bought the MT-90. Likely I will change back to the Porsche fluid if I change it again, but in the mean time there are much more pressing maintenance issues on this 22 year old car... and I am satisfied that the MT-90 isn't likely to cause transmission failure.
So long as your feels tell you you're satiafied, you should be good. Keep up that imagination.

Me? 99% of the time I follow the advice of JFP (and a few others who do more than read...). You blaze your own trail and keep us posted on how that works out for you.
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Old 06-27-2022, 05:50 AM   #8
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Originally Posted by casioqv View Post
Any idea why Porsche would use such a custom fluid when they're just using a VW/Audi transmission that itself has a spec (VW/Audi G 052 911) that is widely matched by a lot of products?

I'd imagine maybe they are trying to tune the 'feel' of the transmission engagement for performance driving in a way VW wouldn't care about?

Still, it makes me doubt that using a VW/Audi spec oil will cause premature transmission failure.

Honestly, I didn't know all of this when I bought the MT-90. Likely I will change back to the Porsche fluid if I change it again, but in the mean time there are much more pressing maintenance issues on this 22 year old car... and I am satisfied that the MT-90 isn't likely to cause transmission failure.
A retired Porsche engineer told me it is because the transmission used in the Boxster has synchro rings made from an unusual alloy that are not used in the gear box when it is in other applications. We have seen similar unique oils used in other applications for similar reasons; the one that comes to mind is the 5-speed used in late 1990's Nissan Maximas, it required a different oil than all other Nissan applications.
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Old 06-30-2022, 07:19 AM   #9
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Originally Posted by JFP in PA View Post
A retired Porsche engineer told me it is because the transmission used in the Boxster has synchro rings made from an unusual alloy
If true that makes a lot of sense. Damn, I guess I'm changing the fluid again after all. I will be more skeptical of what I read in 101 projects from now on...
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Old 06-30-2022, 08:13 AM   #10
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If true that makes a lot of sense. Damn, I guess I'm changing the fluid again after all. I will be more skeptical of what I read in 101 projects from now on...
Over the years, Wayne published several "sub optimal" ideas, such as using set screws to secure the IMS shaft while doing a retrofit; not everything was off kilter, but some were real doozies............
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Old 08-03-2022, 03:23 PM   #11
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I just (today) went to my local Porsche dealer and bought 3 liters of the 'special' gear oil. It was $35.74 per liter

The price is so close to everything else, it seemed there was really no benefit to trying anything else.
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Old 09-01-2022, 10:28 AM   #12
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I promised to report back on Miller from another for thread I believe. I do find it a bit notchy. I am working with a six speed which is well seems to be inherently notchy anyway I'll go back to the Porsche fluid at some point and report back. Just wondering if there's a difference in formulation for the six speed versus five speed

Miller was put in as a substitute for the Porsche fluid without my knowledge or without my consent
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Old 09-01-2022, 11:15 AM   #13
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Just wondering if there's a difference in formulation for the six speed versus five speed
Yes, the five-speed oil is unique to that transmission, and only when it is in a Porsche because Porsche used some custom alloy in the synchro rings that were not used in the same gear box in other applications like Audi.
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Old 09-01-2022, 12:37 PM   #14
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Okay, is there more freedom with the six speed or is strictly another dedicated oil from Porsche? I think I have come across something pertaining to Mobil Delvac being superior…but may have this muddled
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Old 09-01-2022, 12:51 PM   #15
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Okay, is there more freedom with the six speed or is strictly another dedicated oil from Porsche? I think I have come across something pertaining to Mobil Delvac being superior…but may have this muddled
Porsche has always set the specs for their manual gear box oil independently of what is available on the street for general usage. Years ago, I contacted Mobil 1, Castrol, and others about suitable aftermarket products and was told that what Porsche uses is unique to them and because they are such a small market, the aftermarket people tend to "drive a square peg into a round hole" with products they already make rather than make one to match. M1 also called the Porsche factory fill products "very high quality full synthetics". They also told me to just buy the factory stuff for either gearbox and get on with life rather than try to make something work. We did and have never had a problem.

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