Postby smj999smj » Mon May 14, 2012 7:48 pm
"I think the whole concept of running tranny fluid through the bottom of the radiator where could potentially be a mixing of fluids is absolutely stupid. Ruining a 7k tranny to either heat up the tranny fluid or cool it down (I have no idea what their intention was) is dumb."
Radiators with internal transmission fluid coolers have been used for decades by practically every automotive manufacturer. Ideally, automatic transmission fluid should be around 175 degrees F. For most vehicles, the radiator internal cooler is perfect for this job and the only reason to have an external cooler is for severe-duty conditions, such as towing. The best setup is to have the fluid run through the external cooler first and then through the radiator's internal cooler. The external cooler will remove a large amount of heat from the fluid, but if the fluid gets too cool, the radiator cooler will warm it to proper operating temperature. If the fluid out of the external cooler is still too hot, the radiator cooler will cool it further. liquid-liquid coolers are far more efficient than liquid-air coolers.
The problem with the Pathfinders/Xterras/Frontiers of 05-10 is not that the radiator uses an internal cooler for the trans fluid, but that Calsonic made a radiator for Nissan that has had a lot of coolers developing cracks and subsequent issues with coolant being released into the trans cooler line, which takes out the radiator. How many trans cooler failures have you heard of in Maximas or Altimas? Probably none. Titans/Armadas also have radiator problems, but not with the cooler. Their problems involve the bottom tank cracking. These are also made by Calsonic. Some manufacturers (GM comes to mind) even use an internal cooler line in their radiators to cool engine oil, as well.
The biggest problem with this issue is worse than the faulty radiators, themselves; it's that Nissan hasn't stepped-up and recalled the problem-prone radiators despite being aware of it. Sure, they extended the warranty of the radiator to 8 yr./80000 miles, but the majority of the failures are on vehicles that have over 80000 miles but are under 8 years old (Really...what percentage of vehicles are driven 10000 miles a year or less??).
There are a lot of coolers that have the potential for mixing fluids if they fail. For starters, the engine coolant system, itself, can mix fluids if the head gasket fails. Same for oil coolers, like the one used on the VQ engines, if they fail. It's not a common issue, but the potential is always there.