Volkswagen Repair: My 96 Jetta, coolant leak, resivoir

Question
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well thanks for your quick response and your answer. I do know that it was a new part as it looked new and I was there when the VW guy brought it. Apparently it takes 2-3 days for that part. Anyway, he also checked pressure that u mentioned and it seemed ok throughout the system. I was never loosing/leaking coolant just happened all at once. Hpoefully the "new" one is ok and my problem is solved. I'll also ask him about the 2 O rings that u mentioned. Thanks again for your input, I might be back to pick your brain again soon.
Sean Greene

Followup To


Question -
I presently own a '96 Jetta GL 2.0L (gas) with 130,000kms. I'm told the AT fluid and rad coolant pass throught the trans cooler, (but don't mix cause it's sealed). My trans was slipping and fluid overflowed out the top of the coolant resivoir. At that point I lost my AT fluid. I was told that My AT cooler malfunctioned causing the AT fluid AND the coolant to mix. When I took the cap off the ball shaped resivoir it looked like a milkshake. My local garage fixed it (total bill was $480) Everything was fine for a week, then I noticed the temp light was flashing on but the gauge was ok. My tranny was starting to slip yet again. These were the same symptoms as before. Anyway they tell me the cooler was a defective part (what are the odds)and needs to be replaced, and sent back. They will do this under warranty this time of course. My Q is, could there be something causing these coolers to malfuntion shortly after instalation? If so what? Because if this happens a 3rd time they will NOT replace it.Also, what causes the 2 fluids to mix? Hope you can help.
Thanks,
Sean G
Answer -
Did they buy a new part or a used trans cooler? Make sure the second time that a new part is used. Other then the cooler being defective, maybe there is a coolant leak somewhere else in the cooling system causing pressure throughout the cooling system including the trans cooler. The trans coolers do go out occaisionaly, but it is not a big problem. My guess is that the shop you took it to didn't do a proper job. Did they use new seals? There are two O rings that seal the cooler to the transmission.  

Answer
The trans cooler runs the transmission fluid through and it is cooled by the engine coolant. When there is a crack in the cooler the trans fluid and engine coolant mix. As I said before: The only thing that comes to mind is that there is too much pressure in the cooling system and that pressure damages the trans cooler.