mixing synthetic transmission fluid
 

I plan on draining my ATF fluid this weekend, and I know just draining from the pan does not get near all of it out. If I drain it, is it ok to refill with synthetic ATF fluid since it is non synthetic now?

Thanks!

Oh and btw, if anyone asks, yes I replaced the ATF filter last week, so am not doing it again. Just filled with standard ATF fluid and drove it for a week, rather than trying to drain from both places.

Thanks!

I can't speak for all syn fluids, but most are compatible with dinosaur ATF, I know that Mobil 1 ATF is compatible.

If you drain the torque converter you will leave less old fluid.

If you just changed the fluid last week, I wouldn't worry about putting synthetic in yet. At least not for another few thousand miles. Unless you just really like to change ATF.

It's hardly more work to drain the torque converter. Turn the engine in direction it normally rotates until the plug lines up with the access hole in the bell housing. Why would you drain the pan and not drain and not do this extra step?

Sixto
93 300SD 3.0

Because I am in a townhome complex and they do not allow cars to be jacked up. So I must do everything under the car with the car level on the ground. It is hard enough to drain like that, pretty much impossible to do the torque converter.

I am doing a change so soon, in a week, because I overfilled a little bit, and need to drain some anyway. I also have given it a chance to mix with what is in the torque converter.

So im pretty much ok to drain and fill right back up, without the torque converter drained, with synthetic?

Thanks!

You can do it. I don't think there's much benefit. If you can't wait until you can replace 90+% of the fluid with synthetic I'm not sure you should bother.

Maybe you can talk to a gas station about draining it for you. Fill with four quarts then creep to a parking lot to fill with the engine running however much more is needed.

Sixto
93 300SD 3.0

Next time it's at a shop, have them put a mark on the crank pulley so you can tell from above when the torque converter drain points straight down. That way you can turn the crank pulley until you see the mark, then reach under to remove the torque converter drain plug.

Sixto
93 300SD 3.0

I was under the impression that most modern ATF was synthetic. I heard this from a lab tech at Havoline (Texaco). Am I wrong?

Wait! Don't drain it yet. If you have a hand operated vacuum pump (MityVac) you can just draw some of the fluid out through the filler tube. I overfilled my transmission a little bit, and drew the fluid out with my pump earlier today. It's very quick, precise, and it doesn't make a mess.

Good point Logan!

For light fluids like ATF, brake fluid and PS fluid you can use a hand pump. For heavier fluids like engine oil you need something more like a Topsider - http://www.amazon.com/Northern-Tool-and-Equipment-Liquivac/dp/B0000AXBO5

The gravity drain folks will be upset that another newbie is advised of this option :D

Sixto
93 300SD 3.0

Do you or anyone know if overfilling a little can cause shifting problems?

-Thanks

I'm pretty sure that it can. I was driving a little bit overfilled for about 2 weeks, and my transmission had a terrible clunking sound when I came to a stop. I leveled off the fluid today, and the clunking has gone away. So we'll see if it stays gone. Vacuum leaks are next on my list.

Any change is better than none, if you're using Mobil 1 than I know it's completely compatible, change away. If another fluid check the bottle, probably compatible.