The Case of the Disappearing Automatic Transmission Fluid

For a while now, one of my younger sisters has been driving a 2005 Impala. Base with the 3.4L V-6. It has been having shifting issues for the past couple of years. Basically, it keeps running out of fluid until it's bone dry. The mechanics refill it for her, it starts shifting normally for a while, then the shifting performance begins to deteriorate until it needs another refill. Now the transmission is finally dead. According to my dad and to the mechanic, there is no visible evidence of an ATF leak, so my question is, what else could cause the transmission to go through all that fluid?

RexSeven wrote: According to my dad and to the mechanic, there is no visible evidence of an ATF leak, so my question is, what else could cause the transmission to go through all that fluid?

Sounds like an elusive invisible ATF leak. Where else could it go if it is not leaking out? I'll be watching this thread to learn something about the mysteries of automatics.

Is it making coolant?

If the cooler leaks inside the radiator, you're in for a headache.

Shawn

My bet is the cooler lines at the trans. Those quick connects suck for longevity but great for assembly.

Does the engine smoke??? Older transmissions with vacuum lines for shifting used to have the diaphragms fail and suck the tranny fluid into the engine. Of course I am a dinosaur and maybe the trannies are different now.

It's either going out a (probably non existent on a 05) vacuum modulator or into the radiator.

Dad said the car was smoking this last time the slushbox ran dry. He couldn't tell me the ATF fill-up interval but it did get a couple of quarts added about 2 months ago.

All this is academic now. Sis decided she is going to shop for a different car. The Impala has been trouble since day 1 and has pretty much cemented my dad's hatred for American cars.

Here is my theory. Is the coolant funky? If so, the trans cooler is leaking into the radiator. The trans cooler line fittings are also prime suspects.

if the red Dexcool coolant looks extra "Dexcooly", then i'd bet that the cooler in the radiator tank is leaking into the radiator..

Much more common on Neons and Stratuses, but cooler is the likely culprit. Look for an oil slick in the overflow tank. A cousin of a friend had a Ciera that she didn't realize she had a problem until the upper radiator hose burst from being oil-soaked from the inside out. I replaced the upper hose and the radiator, and the car was fine.

I don't think GM used a vacuum modulator on a front drive since the late 80s, maaaaybe very early 90s on the last of the old 3.8s.

Unless it had a leaky intake gasket that was leaking the coolant atf mix into the engine then I'd think eventually something would blow out in the coolant system from slowly being filled with atf.

moparman76_69 wrote: Unless it had a leaky intake gasket that was leaking the coolant atf mix into the engine then I'd think eventually something would blow out in the coolant system from slowly being filled with atf.

That's actually a pretty awesome method of failure, and I say it's reasonably likely for one of those cars.
At least you can get a junkyard trans put in one for like $700 at a shop (or at least you can near me).