Zumkopf

Regarding my problem-child 98 A8Q noted below, with the milky white-tan transmission fluid, I pulled the radiator hoses and the coolant that spilled out looked perfectly normal. I would think if the coolant contaminated the transmission fluid, the transmission fluid would have also contaminated the coolant. So I was wondering if (a) is it always the case that contamination goes both ways, or is it sometimes only coolant --> transmission? (b) Is there any other way for water to get in? The fluid that came out of the transmission when I originally drained it was dirty but not water-contaminated. The car has been on jackstands for several months, with the lower trans fluid-radiator connection detached, and the pan was on loosely for several weeks while I awaited new stainless steel bolts (the OE bolts were rusty toast). No floods, however. Could a significant quantity of water have nonetheless worked its way into the transmission? I can see maybe some small amount of condensation getting in an unsealed system, but enough water to turn the fluid white? Could rainwater on the cowl leak onto the transmission and find its way into the pan if the pan is loose and hanging down a quarter of an inch or so? Or am I just grasping at straws here?

Thanks for any experienced insight,

Z 98 A8Q 140k

hillpc

The fluid pressures in the trans are way higher, during running, than the radiator pressure, so I'd expect more of the trans fluid to be in the radiator than vice versa. Maybe the trans fluid is floating on top of the coolant and you didn't find that yet? After shutdown the radiator pressure stays high for a while, pushing coolant the other way. I'm hoping it was just condensation in your case, but can't say I know anything about it. How much water would it take to turn the fluid white? You mean milk-white? I had a cracked block in a '67 Firebird, and the oil got creamy tan (water in the radiator, instead of antifreeze; color might have been different with antifreeze?).

Test the cooling system with a pressure tester for a second opinion?

Zumkopf

The trans fluid looked like tan skim milk, that's all I can say. I found this article which claims (a) it doesn't take much water, (b) the coolant can get into the trans fluid before vice versa, (c) it's more likely to happen after a trans fluid change, and (d) there is a transmission vent on VWs and Mercedes (and therefore probably Audis) that might also let water in. So I guess the answer is that the radiator is probably bad, but there's a small chance it's OK.

I had the idea to drain the trans fluid (it has to come out anyway), refill the radiator but leave the trans empty, detach the bottom trans cooler hose, run the car, and see if coolant comes out the trans cooler. However, I suspect that even at idle and in park, running the engine with a dry transmission could damage the transmission oil pump.

That leaves me with two alternatives. One, I could just drain and refill the transmission and see if I get the same result. If water got in from some other source, it would be cleaner this time; but if it's the radiator, I simply wasted a lot of time and transmission oil. Two, pull the radiator and have it pressure-tested. Pulling the radiator is no small job, and once I go to that much trouble I may as well just replace it; at 20 years old, even if it's good today, who knows how much longer it would last anyway.

Z
1998 Audi A8Q 140k

jfrahm

I would not run the engine with a dry trans, also there is a lot of ATF in the TC which will come out.

It should be possible to rent a coolant pressure test kit and see if coolant comes dripping out of the trans ATF cooler, with the transmission cooler lines disconnected.

Samilcar

Or you could send off a sample of the milky ATF to be analyzed. ~$25 to find out if it's contaminated with coolant, just water, or neither.

jfrahm

Or if it rained while you had the pan hanging down maybe the heck with it, it was rainwater and you should put it back together and let 'er buck.