'99 5 speed trans oil change, why not fill to overflow? why -11mm??
 

I'm planning on changing the trans oil in my '99 base model 5 speed.
I bought 3 liters of the 'special sauce' at my local Porsche dealer.

I see in the 101 projects it says to fill to 11mm below the fill hole, but online videos (youtube) say nothing wrong with filling until overflow.

Is there any problem with simply filling until overflow? Did the engineers make the fill hole too high? or is it completely fine to fill until overflow?

My tranny runneth over
 

I’ve filled my three Boxsters, my 911’s, and every other manual-transmission I’ve ever had, for 50 years, to the point of overflow, and I’ve never had a problem from overfilling. No oil leaks at the input shaft or output shaft(s) , shift shaft etc. ever. I’ve seen gearboxes that died painful deaths from too little oil. The extra 11mm oil level will make very little difference as the oil is sloshed by car movement, stirred by gear movement, etc. I’m mystified why Porsche makes that suggestion.
11mm? Not 10, not 12mm?

Yes, filling it until it overflows will most likely allow gear oil to leak out the front input shaft bearing of the trans where it will destroy the clutch. The fill spec exists for a very good reason.

Well, they are the engineers and that's what they determine to be correct so why put in more then what is specified?

Would you fill you engine with oil till it came out the fill cap or just go by what is specified?

2.25 quarts is what you need. Don't fill it until it drips. very real risk of getting fluid all over your clutch

Input shaft has an oil seal so overfill won’t immediately cause leakage and wet clutch…. But regardless it is specified for reason, and I trust Porsche engineers know how fluid sloshes around when the car is in motion… not logical reason to fill to the plug hole.

Because the 5-spd tranny is from Audi, the hole location was not originally designed for Boxster installation thus the height spec., I guess…. It’s not a big deal to check it, if you can bend and mark a paper clip. Can be done faster than typing up a question here.

Ok, this is exactly why I asked. The hole position was not originally placed for this exact set up.

I will DEFINTELY do the -11mm from the hole.
I'll add the 2.25l and check from there.

Thank you everyone for your inputs :0)

Interestingly the 6 speed is filled to overflow so I suspect they put the fill hole in the right place.

Right, Audi did not design it obviously…

To see is to believe! My 2001 was sold with a "bad" gearbox. It was extremely difficult, almost impossible to shift, but the price was so good that I planned on finding a second hand gearbox and swapping it out.

I did the usual checks with cables, linkages, and adjustments and everything was OK. I was stumped and already planned on a replacement so I decided that what the heck, I'll do a fluid change. When I pulled the side fill plug to vent, oil just shot out like it was running from a faucet. Clearly somehow the level was much higher than 11mm below the fill plug. Not sure how it happened but luckily no leaking into the clutch or anywhere else.

Drained and refilled with the correct fluid (also important) 11mm or so from the top of the fill hole as best I could. Shockingly, the gearbox was back to normal immediately and has been just fine for the last 4 years.

Well, that was a long speech. Sorry lol. I would say, and especially with German cars, to follow the factory recommendations. For all the other British, Japanese, and American cars I have owner I never cared or worried about those kinds of things at all.