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YOUR RESEARCHBest Gear Lubricant (Transmission Fluid)
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Fill with motul synthetic gear oil
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Leading evidence: 'Fill with motul synthetic gear oil' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, The most frequently discussed action is 'Fill )' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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My independent specialist changed the Transmission Oil.
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I run Porsche transaxle fluid on all 4 P'cars now.
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I'm old enough to remember when pretty much every used car had a worn out 2nd gear synchro.
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After all this research, I am still not sure which one is the best, so am going just make a choice.
Well, I went down the rabbit hole... and I came back up with no definitive answer. I am trying to address a shifter that does not like to shift when cold. It mostly does ok when warmed up, with some 2nd gear quirks. My last 996 was not like this, so I am on a quest to fix it. Starting with replacing fluids.
The car has 109k miles and doesn't have an LSD. After fluids and clutch bleed, I plan to install new Function First engine mounts, FF transmission mount insert, FF classic shift **** and the FF Shift Right Solution. My cables are in good condition, so I am going to skip them for now, but if it's still an issue, I might try them later. Gbox makes an upgraded 2nd gear detent... doesn't seem to be my issue, but it's on my radar. Last stop, good old transmission rebuild. So, I am hoping fluids help tremendously...
Here are the main options I found:
Swepco 201 80w90
Mobilube PTX 75W-90 - 00004320420L
Porsche Classic Gearbox Oil - PCG04321052
Porsche Manual Transmission Fluid - 99991754600
Mobil 1 Delvac 75W-90
Motul 300 75w90
Luiqi-Moly
Red Line
Shell SPIRAX S5 ATE 75W-90
Amsoil 75w90
Miller's 75w-90
After all this research, I am still not sure which one is the best, so am going just make a choice.
That said, I thought I could compile all the recommended options in one spot for anyone asking the question in the future. Good luck whoever you are...
So, what fluids do you all recommend? anything to add to the list?
I’ve tried Motul and Shell (supposedly the factory fill). The Shell stuff was very hard to find in reasonably volumes, however I would say is “slightly” better than the Motul when cold. That said, I don’t think I’d go through the hassle of finding it again and would go back to Motul or maybe something else.
I've used:
- Swepco 201 80W-90
- Porsche branded 999999999999999
- whatever was in the car when I got it
None of them works well when cold. The Swepco is particularly unhappy at lower temps, by which I mean winter north of the Mason-Dixon line. But it gets over it very quickly, and it shifts wonderfully the rest of the time, which I can't say for the other two. Both of the others made 2nd gear miserable, particularly on the way down. The 201 cured that. For now that's my choice, at least until Tremec steps into the fray with a proper solution...
If your second gear is noticeably different from the rest of the gears you have a worn 2nd gear syncro...period...
2nd gear gets abused the most because it is in the "sweet spot" where people like to rawhide their car without getting too much speed above the speed limit...( 2nd gear will carry to above 65 mph)
I've tried Mobil1, Redline and finally Porsche Classic in our 996 and 986 S. The Porsche is the best all-around especially when, the Mobil1 was OK, but the Redline was terrible when cold and very 'notchy' at operating temp. I run Porsche transaxle fluid on all 4 P'cars now.
Yes I know, but please don't hate me for trying to give it a few more years of life.
I'm old enough to remember when pretty much every used car had a worn out 2nd gear synchro. Double clutching was almost a necessity.
Somewhere on RL there is a "mega thread" on transmission oils. I read all the transmission oil threads extensively before I chose what transmission oil I used, and the "in my head" consensus of all of that reading was that the factory OEM Porsche transmission oil seemed to have the fewest complaints, I would say by a reasonable margin. Most of the posts were about people hopping around the various name brand oils (everything but OEM) trying to find something better than OEM, but OEM seemed like the safest bet from the comments.
I replaced mine with OEM transmission oil (probably replacing original OEM). I had no shifting issues before cold or warm, but it did shift a bit better with the new oil.
My view/experience with transmission oils is that which oil works best is much more about "compatibility" with the transmission design, than "quality" of the oil. I'd recommend using the Porsche OEM oil, then try something else if that doesn't work.
What I've found is that if I caputre all the marketing material from the OEM stuff and compare it to the aftermarket often times the aftermarket stuff has more of everything. I used chatgpt to help me compare the two:
For a classic Porsche 911 (915 or G50 transmission)
→
Porsche Classic Gearbox Oil
is the safer choice due to its
GL-4+ rating
, preventing premature synchro wear and ensuring smoother shifts.
For a modern Porsche differential (non-transmission use, such as a limited-slip differential in a 996/997)
→ AMSOIL 75W-90
GL-5
is a great option.
My 99 996 C4 150k miles on it . I bought it as a roller as the engine was kaput . So I never drove it with whatever fluid the previous owner had in it . While my 3.8 engine was being built I drained the old fluid out of the transaxle and front differential . I filled with Motul synthetic gear oil . She shifts like butter but is finicky cold for like a mile . After that mile it is the smoothest water cooled manual I have ever driven .
Oh Sorry Dave...I didn't mean to throw a monkey-wrench into an oil thread...
Yea I have no problem with anyone trying to get another year or two out of worn syncro's...carry on !!
I would think this is from people "rushing the shift" into 2nd and making the synchro work harder, since by the time you're in gear and accelerating through 2nd the synchro has already done it's job - is that the right way to think about this?
Yes exactly !! Plus there is a big drop in ratios between 1st and 2nd so just waiting a second between the 1-2 sift will save the syncro....( lets the RPM drop just enough so the syncro doesn't have to work) and then a little rev ( rev match) on the downshift and you will never have any syncro wear...
But most Novice aggressive drivers wont wait for the RPM to drop and will force the syncro's to match the internal gear rpm on the 1-2 shift......and when rev matching on the downshift will over-rev/under-rev ..( also causing the syncro's to work hard)
I admitted in an earlier posting that I double clutch 1st-to-2nd when the engine is cold. Works every time! (And slows the shift.) BTW, use the Porsche fluid.
I swapped my motor mounts, added the function first transmission mount insert, and swapped my fluid.
my motor mounts were toast, should make a big difference.
My car was fully service 3 weeks ago
My independent specialist changed the Transmission Oil.
He suggested me Sunoco.
What a great oil! now the manual transmission runs incredible!
Just like engine oil, I bet there are quite a few gear/trany fluids that are excellent. Probably starts with an understanding of the differences in formulation thru oil testing to level set. And then an understanding of what formulation is required for our Trans for functionality and durability. Just like we do for engine oil.
It would be a good discussion.
When you say that the Redline fluid notchy, what do you mean? Like, when you would go to slide the shifter into the next gear, it would sort of fight you? And which Redline fluid?
Notchy as it felt like the transmission 'clicked' into engagement, like a rifle bolt feeling. I could live with it, liked it actually, but not at the expense of feeling like I was forcing the car into the next gear until the transmission warmed up. Odd as I have had great experiences with Redline in vehicles from early Land Rovers, Triumphs and 70's BMW's...
Swepco 201 has been a standby for years. Just doesn't like the cold.
I use 201, Driven, or Millers. To be perfectly honest, just changing the fluid more frequently is simply the best thing you can do.
Unless you are tracking the **** out of your car, 15k is far too often. If tracking your car, I'd do it once a year, bare minimum, regardless of mileage.
It's hard to say exactly when you should do it, but on my cars with automatic transmissions, I usually do a fluid and filter change every 2 years or 24,000 miles and do the gear lube every other ATF/filter service. Hope that helps.
