Dear analogdad,

Hope you're well. About a year ago, I dismantled a replaced radiator. I detached the plastic side-tank and so exposed the automatic transmission fluid (ATF) cooler. The ATF cooler is a double-wall, foot-long copper cylinder, with a hose nipple mounted perpendicularly at each end. The hose nipples protrude through the side tank's walls. The steel ATF fluid pipes attach to those nipples.

The ATF cooler's copper wall is thick: it would be hard to twist the nipple enough to crack the copper, where a nipple joins the ATF cooler's cylindrical body. Twisting the nipple - by not holding it with a wrench, when loosening the ATF fluid pipe hex nut - would break the seal between the nipple and the inner wall of the radiator's side tank. This would cause a coolant leak, but not allow coolant to enter the ATF.

In short, this "post-mortem" suggests it will take a lot of twisting to create a crack in the in-radiator ATF cooler. If this happened, pressurized coolant could enter the ATF after engine shut-down, when the ATF no longer was being circulated by its pump, but while coolant was still pressurized, albeit not by the water pump.

Hope this helps.

Yours faithfuly,

Spook