Gearbox oil choices

Planning on changing the gearbox oil on my ‘08 Boxster (base) 5-spd manual and after reading numerous threads and articles on options to choose from, I’m still on the fence over OEM vs. aftermarket. Seems as though half the ownership insists on not straying from Porsche original fluid, and the other half stands behind some of the well known brands out there, such as Red-Line, Motul , etc. Cost is not the issue, as with any DIY job the savings far outweigh counting pennies when selecting the best product for the application. OEM goes for $40-45 per liter, while aftermarket runs about $25/l. In the end, I feel like it will be a coin toss anyway but I value the opinions of our seasoned knowledge base with its combined years of experience and expertise. What have others been using, and why? Thanks in advance for any feedback.

Well, it was in the 6-speed, but I tried the Redline 75W90NS and didn't like it; it made the transmission balky in the cold. I went back to the Porsche -branded fluid and it worked well. I believe the Porsche stuff is just Mobilube PTX 75W-90...it's not like Porsche 's making gear oil. But there wasn't much of a price difference between the two (at least, not at the time) so I just bought the Porsche stuff.

I went OEM as well. Too many times I've put the latest greatest in and it felt like crap. Even Redilne. OEM for me.

FWIW, a friend of mine works of Infineum and is a tranny fluid R&D guy. With his 2008 987 BS, he went with Redline 75W90 and I did as well although I was contemplating with Mobil DelVac 75W90. The Redline works well for both of us.

Im considering Schaeffer’s but my mechanic is also pushing for oem so ill likely go that route.

Do these recommendations also apply to PDK gear oil?

Thanks to the community for your input on this topic. Found some more old posts on this going back a few years and the majority of posts reference using either Porsche OEM fluid or RedLine. RedLine has a good reputation, with many posters using it and reporting no issues, but when it comes to peace of mind, using the fluid that Porsche initially puts into their cars when built is proof enough for me. And judging by the content of some of the feedback, there were no regrets over using OEM, but a small percentage that went aftermarket and experienced issues, causing them to revert back to OEM. Probably leaning towards going with the OEM, so I don’t have any trepidation over my choice.

Don't think so...per my buddy (but not specifically for PDK ) auto = always OEM, manual = relatively "simple" mechanics so Redline is fine (and apparently Redline has the "right" additive for our synchros).......(without getting into the details) for autos, lubrication is secondary, and friction / friction modifier is the primary, hence auto = OEM. He also developed "universal" ATF but only uses OEM for his other auto vehicles

I advise using full synthetic gear oil instead of OE or aftermarket conventional. Regardless, you might find my write-up helpful. True, it is for the 6sp, but many of the details will like still apply. https://www.planet-9.com/posts/857935/ PS - I recently used this same NEO gear oil in my 2021 Cayman GTS 4.0 6sp manual.

I see it, Pentosin is full synth. Actually, I also just saw that Advance Auto is clearancing this out: Pentosin FFL3 Full Synthetic Double Clutch Transmission Fluid: 1 Liter 1052107 - Advance Auto Parts

I'm coming from 997, but we are talking the same. The PTX is a weird hybrid GL4/ GL5 mix, and I can tell you now that nothing else comes close to super crisp gear changes, on a manual more noticeable. In fact half the issues people have are when moving away from this. Even Porsche went to Delvec and then moved back. The closest compatible is Redline 75w30 NS or Motul MotilGear (Do not use Motul 300!). I have tried so many different gear oils and the difference between PTX and the rest is the huge. On a manual 1st gear is hard to engage until warm, second gear spongy or worse pops out, but the main thing is you can feel that rifle bolt gear change with a manual, it is effortless and precise, the gears snap into place. Same thing will be happening with PDK cars, just hidden because the automation is doing the work. But this is one time I would say stick with the factory fluids, the PTX is so much better than everything else. People who thought they needed a gearbox rebuild have gone back to PTX to find it is the best they have ever had it feel.

Mobil 1 Delvac full synthetic 75W-90. Recommended by a garage mate when I was at VIR. Research has revealed that Porsche uses it in their Motorsport (GT) race cars (back when they were MT). Not for PDK obviously. Since I started using it and changing gear box oil yearly because of many hot, fast, track miles, the shifter feels like it slips between gears so smoothly.

My 6sp 2006 987 Cayman S has been using Mobil1 Delvac with LiquiMoly gear additive for the last 50,000 miles, about 14,000 of which now are track miles. Why? Because I discovered that Porsche had/uses that exclusively in their MT Cup Racing cars, I felt if it was good enough for those beasts then it's good enough for my mine. No issues with the transmission or shifting whatsoever. To note, the LiquiMoly additive has helped with cold weather shifting a bit. It has almost 120,000 miles on it now.

delete

We both must have been typing this info at the same time... LOL

Glad to hear from someone else that isn't afraid to put a few miles on. Mine is only at 110,000 and has been put away for the winter.

My Porsche dealer said all you need is one that meets GL-5 and they use Mobil 1 75w90 for manual transmission.

So here's the thing: pretty much any 75W90 GL5 gear oil will meet the spec and will protect the gears and the ring & pinion. Where things can get quirky is the transmission synchronizers. Those rely on friction to work, and subtle differences between gear oils can cause differences in shifting performance and feel. Some transmission designs will shift fine with anything, some tend to be on the more finicky side. The 987 (at least, the 6-speed Getrag in my CS) seems to skew towards "more finicky" given it didn't seem to like the Redline 75W90NS all that much. So my suggestion is to stick with the OEM stuff, which from all reports appears to be Mobilube PTX 75W90 but don't quote me on that.

Here is where things are tricky with a transaxel. GL5 is best for differential due to the high gear face loads on the pinion. GL4 is best for synchromesh transmissions because you actually want a little bit of friction under high face loads to make the synchronizers work well. There are very few GL4/ GL5 oils available. Mobil1 was, but is no longer. I believe that Valvolene Synthetic still is rated. Lots of gear oils say "suitable for GL4/5 used but we really need "rated for" or specified for.

The genuine Porsche oil -Mobilube PTX 75W-90, is basically impossible to get in Australia. In fact, it looks like our easily available choices are pretty limited. My 2006 987.1 S Manual, with Numeric short shift is nice when warm, pretty difficult to select 1st when cold. I’m not sure what oil, or when it was last changed - so I’d be keen to change it. Twice in quick succession if the first lot looks really old. Lot’s of opinions/advice, some conflicting. I understand the oil also lubricates the diff - I have a Wave-Trac LSD . So competing needs potentially. Difficult to be sure - I guess - Pick a likely suspect, and see the results. Hopefully smooth shifting will also align with good protection.

Can you get Redline products? I mean, the Redline 75W90NS wasn't bad , per se, it just wasn't quite as good as OEM in my opinion. And it's got the right specs for your car. The NS doesn't have LSD friction modifiers; I don't know if the Wave-Trac is a clutch type or not. If it is and you get LSD chatter you can just add friction modifier until it stops, but as you noted it's always going to be a tradeoff between synchronizer performance and LSD performance.

Actually I should search first. From the Wavetrac FAQ it's a gear-based design and they do not recommend LSD friction modifiers. So the straight Redline 75W90NS would be a good choice in your case, if you can get it. FAQ Wavetrac limited slip torque biasing differentials. www.wavetrac.net

FWIW, I recall using Redline 75W90 on one of my previous cars (Mazda MX6, manual trans). The redline wasn't great there... and most of the forum users recommended Pennzoil 75W90 instead. Like this stuff: 75W-90 Synthetic Gear Oil | Pennzoil® That fluid was great on the manual trans, and made shifting a lot smoother. IIRC, I changed out the Redline soon afterwards, because I really hated the shifting issues. As I recall, it was an NS as well (no friction modifiers needed there).

Thanks. I’ll look into Redline. The Wavetrac info says “use what the manufacturer recommends. Or use Motul 300.”

If you can get the Motul 300 that looks like it could be a good choice too. It meets GL-5 specs for the diff but is also recommended for gearboxes doesn't seem to have LSD additives. So pretty equivalent to the Redline NS spec-wise, though no personal experience with how well it works with the 987 synchros.

Try rolan.com.au for the Redline 75W90 NS GL-5 Gear Oil. I got it from there in a gallon bottle - although right now I can see it only in quart bottles.

Have I got it right: GL5 is best for the 6 speed manual GB GL4 is recommended for the stock diff? The Wavetrac, gear - not clutch type, LSD diff is happy with GL5 but not LSD oil or additive. (They recommend either what the car manufacturer specifies or Motul 300) So really, any high quality synthetic 75W90 gear oil should be ok. Preferably a brand others have had success with eg TRANS GEAR 75W-90 (Full Synthetic) | Penrite Oil Trans Gear 75W-90 is an SAE 75W-90, premium performance full-synthetic manual gearbox transaxle oil. It is manufactured from a blend of highly refined base oils, the latest technology additives, friction enhancers and an advanced viscosity modifier. It meets the performance requirements of API... penriteoil.com.au

No, Afraid not. Most are awful. Motul 300 75w90 is horrible, really not good at all. I wil quote myself here, done testing with around 12 different transmission fluids and this is what I would recommend......

The issue is our transaxles have both a synchro transmission and a differential bathed in the same oil. Hence the need for a GL4/GL5 oil.

Skypig, you need either.... Redline 75w90 NS Motul MotilGear 75w90 (This is a GL4/5 semi synth. very similar to PTX). PTX is so, so much better than the rest though. You can get it in Aus in 20l drums. I the UK we are the same. We buy 20l and then 4 cheap plastic jerry cans and divide it into 5 and sell to others. They sell in around a day on the forums.

Really appreciate the effort and answers. Looks like PTX it is - no matter the difficulty and expense. Manual gear changing, especially heal/toe is one of the joys of this car - need it as good as can be. Mine is currently “difficult” into first when cold. All seems good once warmed. Numeric short shifter . Last change 3 years/20k km (12k miles) ago. Indy specialist lists “85W90 Mobil Gearbox Oil”??

Mobil 85w90 is a GL5 oil. Can make 1st gear a pain until up to temperature and can make 2nd gear feel a bit rubbery. These cars should feel like a rifle bolt as they snap into each gear. One other tip, don't over fill. Look at the amount needed and put that in. If you fill till it drips from the fill hole, wait for it to stop and suck out 50ml. Slightly too much turn the gear shift rubbery too. I have Redline in mine at the moment, one of the very well know Porsche specialists put it in about 7k miles ago, it is passable, but I have bought 4 litres of PTX, I have a weeping rear drive shaft seal, so waiting to get that done before putting the PTX in. As the weather has got colder you can really tell when a car has not got the right PTX stuff in. I tried the Mobil SHC(Think this is called Delvac too) that Porsche sell in 1 litre bottles. That was terrible, 2nd gear was really horrid and even popped out. I'm sure half the people who rebuild their gearboxes just needed to put the correct oil in.

So now the hard question: Should I replace the SWPCO 201 in my 914 with PTX?

No freakin' way. Swepco 201 is the best stuff I've ever found for older-style synchros. If the OEM Mobil PTX didn't work so well in the 987 I'd be using it there too.