That Pelican guide should really be a little more explicit about which instructions are for which transmission. I double checked my Bentley manual, and for the 5-speed it should be 11mm below the fill hole.

Damn!! Is overfilling bad?? I can't get back to the lift for atleast 2 weeks! Will it be ok?

Overfilling puts an extra load on the gears inside the transmission. You can draw it down without a lift. Floor jack and jack stands do the job.

The larger issue with overfilling the gear box is oil getting onto the clutch via the input shaft when the oil gets hot.

I will try and do this in the next couple of days. I still need to remove the aluminum tray and diagonal brackets covering the transmission right?

Not sure. I have the 6 speed and the fill plugs are in different locations.

Save time, effort and a lot of potential alignment issues and drill an 2" diameter access hole in the tray. You'll be happy you did.

To remove just a little fluid, remove the fill plug and jack up the from end, some fluid will leak out the fill hole and then level the car and see if the 11 mm difference is met.

Awesome, thanks! Can you explain the potential alignment issues?

The hole will give access only to the drain plug right? I am not sure if i can access the fill plug without remove the tray.

You should be able to get at the fill plug with the tray in place. It may be a bit awkward but accessible. The fill hole for the 6 speed is more accessible.

The alignment issue comes into play when the tray is removed. It is a bear to get back in and align it with the bolt holes in the two support arms. Wrestling it back in is a pain and could result in things not lining up correctly.

This is right, 2000 and older use a special oil. It is not the same oil for the later models as Rick very correctly states. It will make a difference, I went to the dealer and they sold me the gear oil for the later models, and its did not work, the shifting was balky and when I put in the correct oil, it shifted perfectly.

I spent a few hours researching the transmission oil for the '99 before I changed mine. Porsche really went all out on the early five-speed's and the oil is in fact specific to the transmission. It's a shame most dealers will try to sell people the wrong fluid, because they don't stock the 20L drum. Don't trust the parts guy at the dealer!

The plate is part of the suspension system, it acts as a brace between the rear suspension, and when you remove it, you can change the alignment of the car. If you choose to remove it and not drill a hole, use jack stands and not ramps. By taking the weight off the wheels you will reduce the chance of messing up the alignment. When I removed the plate I used stands, and when I had my alignment checked afterward it had not been affected. :cheers:

I was due to change my transmission oil ('01 S, ie 6 speed), so I gave my semi-local Porsche dealership a call. Turns out what they sell for DIY purposes is Valvoline 75W90. I guess I'll check with the folks at Sunset. In the 101 Projects book Wayne also mentions using Mobil Delvac Synthetic Gear Oil. Anyone have any experience with it?


My driveway is sloped. When I do an engine oil change I point the car uphill then back it onto homemade ramps. By finessing it a bit I can get the car nice and level and still have access to shimmy underneath and reach the drain plug & filter.

With changing the transmission oil, if I did the same thing but, instead of using ramps, jacked the back end up and then put it on jack stands, could I avoid the potential alignment issues? The other thing I'm wondering is this: I feel very safe under the car on the slope using the ramps for doing an engine oil change. OTOH I'm suspecting it may be a bad idea to use jack stands on a slope, even a pretty gentle slope like what I'd be working with. Actually, if I do it right I can have just the front end of the car on the sloped part of the driveway while the rear end (where the jack stands would go) is still on the flat part.

When you guys have done the transmission oil have you put the car on stands on all 4 corners? (I wish I'd bought a lift years ago... :rolleyes:)

I just noticed that the Mobil synthetic transmission oil question was already addressed earlier, so I probably don't need any response on that. OTOH, if anyone's used it and found absolutely no decrease in performance or smoothness of shifts, I'd be interested in hearing about it.

Is that same socket for 2003 Boxster 5 spd Trans.?

I'm newbie I just purchased this car 3 months ago has 71K miles no service record or one's manual. When do I replace the Trans. Fluid? at 100K ?

According to Bentley should be the same socket.

On how frequently to change the transmission oil opinions vary. The Bentley manual (which I assume is based on Porsche recommendations) says only every 90k miles. Wayne, in his 101 Projects book, recommends every 30k miles. I tend toward somewhere in between.

30 to 40K miles is the optimum window, depending upon how the car is used (track cars change sooner).

I'd listen to him...he kinda knows this stuff pretty well.. :D :D :D

New info: I contacted the folks at Sunset, asking about their transmission oil. He replied, "This is the Mobilube PTX 75w90 transmission fluid. Porsche only sells it in 20 liter containers so we break it down in to individual liters for our customers."

I was thinking the "Porsche stuff" was a Shell product. I'm not sure exactly what constitutes OEM transmission fluid in P-cars anymore. Is this Mobil product the one that is so much better than the other oils out there? The stuff that you, JFP, have had customers drain out other transmission oils to put in?

Porsche currently has two approved 6 speed lubes, this is one, the other was a Shell product. The early 986 base cars with a 5 speed used a totally unique product which was made by Burmah, which is also a Shell subsidiary.

Okay, now we're gettin' somewhere.

So, when people say it's best to use the Porsche transmission oil, that it's so much superior to the competition, that would apply equally to both the Mobil and the Shell products?

BTW, I have no axe to grind here...I'm just trying to figure out what's going into my gearbox. :cheers:

Looking at this again, I should re-word: Not what "you, JFP, have had customers drain out other transmission oils to put in?"

What I meant to say is what "you JFP, at the request of your customers, have drained out of transmissions to put in?" I'm pretty sure you weren't holding a gun to their heads.. :p