Do antifreeze and transmission fluid mix

May 12, 2009 3:45 PM

Someone I know (cough me /cough) put antifreeze in a transmission. Will it blend?

This person discovered a very large puddle of red fluid under their car this weekend. I, um I mean they, assumed it was transmission fluid even though it smelled sweet and the only fluid that indicated low was the coolant reservoir. A drip pan was installed beneath the car to capture whatever fluid remained. About six quarts came out all told.
One of those quarts was poured into the transmission via the dip stick for fear that driving the car even one mile to the mechanic with a transmission leak would be very bad. Once at the shop, the mechanic determined it was a bad hose, not anything related to the transmission. Apparently, GMC puts something called Dexcool permanent anti-freeze in their cars and it is red, not the normal green one would expect of coolant. Our hero wonders if they should have the transmission flushed and if even that will save this transmission from certain doom?

posted by toomuch to travel & transportation (10 answers total)

Well, you should ask your mechanic, but if it were me I'd absolutely have the transmission drained and flushed, though I'd say have it done by the mechanic, rather than a Jiffy Lube.

Do I read you right, that you already ran the car? If so, drive it back, tell the mechanic what happened and have it flushed. I wouldn't think you've done permanent damage yet.
posted by Pantengliopoli at 3:49 PM on May 12, 2009

The car has only been driven to the mechanic, where it currently sits. I'm happy to have him do the flush but is it possible that it's already too late? Is there some antifreeze/oil chemical reaction that will eat through transmissions like the alien blood on the Nostromo?
posted by toomuch at 3:53 PM on May 12, 2009

Yes, you want the transmission flushed. Do you want to drive for the foreseeable future with coolant in your transmission? Did you tell your mechanic about this? I'm sure your mechanic would recommend that you get the coolant out of there ASAP.
posted by ssg at 3:53 PM on May 12, 2009

I'd be more concerned about the anti-freeze foaming and damaging seals within the transmission, but this is all sort of moot -- 100% for sure get the transmission flushed and see what your mechanic thinks it's likely to have done. My guess is that, when flushed, if the seals look good and it still runs well, you're in the clear. I doubt you'll have a Nostromo effect, but keep Jonesy out from under the car just in case. ;)
posted by Pantengliopoli at 3:56 PM on May 12, 2009 [1 favorite]

I agree with above.

I seriously doubt that it is absolutely jacked. The fact that the tranny did have the requisite amount of the proper fluid probably helped a great deal. If you, or uh, our hero, had somehow exchanged the fluids and driven it for a bit, they would be in worse territory

Our hero should flush it and refill it.
posted by milqman at 3:56 PM on May 12, 2009

Oil and coolant are not going to combine to eat your transmission. Get that mix of stuff out of there, some proper transmission fluid in and be on your merry way.
posted by ssg at 3:57 PM on May 12, 2009

Water and coolant in the transmission fluid can't be good, if that's what you're asking, but I don't know if it will kill your transmission either. I'd play it on the safe side and replace the fluid in the transmission.
posted by zippy at 4:00 PM on May 12, 2009

Transmission flush: done and done. Do not pass go but be sure to pay the mechanic $200.
posted by toomuch at 4:05 PM on May 12, 2009

Thanks everyone. I'll be sure to pass along the sage advice to my "friend". The moral of this story is to trust your initial instincts and the data at hand. If the dip stick shows full even when you are presented with mass quantities of fluid below the car, the dip stick is right.
posted by toomuch at 4:08 PM on May 12, 2009

If you put old rusty coolant into the transmission you are likely screwed. You need the system flushed not just drained & added to as the torque converter & cooler holds back fluid. If you only drove a couple miles then flush & drive 10 miles or so (to get all warmed up & flowing) If it still works drop the pan & put in another new filter & more new fluid. You might get lucky.
posted by patnok at 7:57 PM on May 12, 2009