I've posted this on a couple other sites, but I figured I'd spread the love. So I ust had my 727 auto transmission rebuilt on my 345 78 Scout "grouchy", and the tranny shop strongly discouraged me from adding an auxiliary cooler. They said that the 727 needs the heat and that, especially in winter, an auxiliary cooler won't let the fluid heat up enough, and that there'll be condensation inside as well. This surprised my mechanic as well, but we both figured we should defer to the expert. Any thoughts? I won't be towing with this anytime soon, and nothing too extreme in the four wheeling either. Thanks
I would totally disagree with your "tranny shop" analysis!! They certainly did not explain to you the ramifications of adding an auxiliary heat exchanger in a proper manner!!
Any auxiliary unit should be plumbed in series with the existing setup and never installed in stand-alone mode unless a thermostatic control valve is added to the transmission plumbing along with the heat exchanger.
An automatic transmission uses a working fluid designed to operate within an optimal temperature range. Engine/transmission heat load is handled by the oem radiator package just fine, but for any service involving increased gcwr, then that package quickly is overworked. That is when an auxiliary cooler is called for even for occasional use.
Summer...winter...makes no difference to the powertrain operation if the entire engine cooling system is operating correctly. The radiator and engine cooling system package determines the working temperature of the engine oil and the transmission oil. And all the various "temperatures" are kept under control by the vehicle heat exchanger and the cooling system thermostatic control (if working properly). But when significant added load is added to the system over and above normal daily driving such as towing a trailer, an on-board "overload" of say...sacks of concrete, or slogging up a long incline at low ground speed and high engine rpm (when the transfer case is in low range), an auxiliary cooler is totally necessary in my opinion and I'd never build a transmission for anyone and stand behind it if the rig did not have an auxiliary tranny cooler installed.
The vehicle cooling system for any given engine/powertrain option was spec'd for a minimal ability to provide adequate temperature control for the spec'd gvwr of the individual vehicle. Add in any increase in load above the gvwr and engine cooling overall quickly becomes unmanageable.
That also happens to be the standing policy of the atra and their "member" transmission professionals as far as the blanket warranty they offer on a trans built by an atra member shop.
The effective "normal" transmission oil temperature range for a tf727 is no different compared to any other slush box of that era...a Ford c6, a GM turbo 400, etc. That would be a "low" of about 160f and a "high" of around 240f, these would be temps encountered for an extended period and not just an occasional anomaly.
All the above is in reference to vehicles/transmissions of the era in which we deal with around here. You cannot draw a comparison with more "modern" vehicles that incorporate computer control in the engine/powertrain module. The temperature control of all that throwaway shit is far more complex and involves changing shift points, disabling over drive or converter lockup, putting the engine/trans into "limp" mode, etc.