Transmission Fluid Change - Is The Car Being Level Critical?

I have been changing the tranny fluid of our Acura MDX on ramps. I basically measure what came out and put the same amount back in (for years). Just wondering whether I can / should do the 2005 Boxster 2.7 (5 speed) with only the rear end jacked up - I have a cross beam for my floor jack (which barely slides under) so easy to lift the back all at once. I understand the "proper" way is leveling the car (and my garage is not perfectly leveled either) and measure with a paperclip but as long as I can measure exactly what came out, and pump in the same amount, I should be good to go, perhaps? I don't think our tranny fluid (e.g., OEM or DelVac) expands (based on the temp) like our Subaru's CVT fluid, and just wanted to check whether this approach is detrimental - I don't track or autocross Thanks for your input!

It probably won't matter for the manual transmission as much as an automatic, but I would want to know if the fluid level was right before I started, and to make it right when I was finished. If you don't see any seepage around the axels and bell housing, then it may be okay?

A great point as I was assuming the original owner has not change the tranny fluids as the car had 74k when I bought it - i.e., factory fill. No leaking as the underside is rather immaculate. Thanks for your input!

Yes, it is important to have the car level with every car I have ever changed it on that uses a fill/top off hole and drain hole. Over the years I have even done it on slightly angled driveway BUT I leveled the car with jack stands that have ratcheting bars and even using a piece of plywood under them to get it fairly level. With that said your method of measuring sounds ok too but I would measure what came out of your car and compare against the specified amount for your and and go with the one that is greater for an extra margin of safety in case there was a leak you didn't know about. Also, I my pump has never been able to pump the whole amount into the car, it always leaves a bit at the bottom so you will have to add extra and guess to get the "measured" amount back in. For that reason, I would try first to level the car. It doesn't have to be perfect but basically level. There are other benefits to learning to level the car...like brake fluid flushes, coolant flushes. Best of luck.

Close to level is good enough. In previous cars I have even tilted them to get more out. But for my 981 I do it pretty level. And of course put back in what came out. Usually I add 100-200 ml more. I like to see it flowing out of the fill hole pretty good, before I put the plug back in.

great points . Yes, my $9 pump always leave "some" but I just pour the remaining into another bottle Thanks for the insights!

The technique of measure and fill the same is time-honored with a number of good mechanics I know. It's how home changes of the hydraulic circuit fluid in the PDK transmissions by a DIY'er is suggested to be done (in that case, the car is jacked on one side - the side the fill port is on, since the fluid may rise above the fill port if the car is level..) It's a valid technique. On a manual transmission, the exact level isn't super critical, 50cc's isn't going to make ANY difference at all, the lubrication isn't by immersion, it's splash - as in the fluid getting splashed around all over (eventually creating an oil mist) by the rapidly rotating gears in the trans. On a PDK , I'd try to get it within 100cc or so, erring a bit on the high side perhaps. The actual PDK gearbox (there are two oils used in a PDK , clutch/control oil, and gearbox oil) - the gearbox part is equally uncritical since it's actually just a gearbox (no clutches or hydraulic controls in it.)

Don, as usual, your wealth of experience and knowledge is very helpful. For our other cars, I probably overfilled a bit (the diffs) as I do the fluids on rhino ramps ....thanks!!!

Thanks for the info and just wanted to double check for any " Porsche -specific" things although my buddy says the manual tranny (Getrag, I think) is very simple so don't worry as current "regular" passenger car's CVT / auto fluids are more complex to deal with

Manual is so easy I would change it often. My PDK the rear gear oil is like the manual. When I opened the fill plug with the car level nothing came out. I never had any leaks, but this concerned me. But it was just below the hole. When I refilled I made sure it was pouring out the fill hole. I will likely open the fill hole with the car level and check it in a few months when I do the clutch aside again.

Seems like a reasonable theory provided what you take out is equal to the factory fill.

I agree, only possible issue was if you had a small leak and you were under filled. Then you are filling to an underfilled state again. I made sure I put in what came out and I think about 100ml more. It was flowing out the fill hole pretty good.