And a second opinion:  I have an AOD with a 2800 stall TC.  I have the two row, 20" aluminum rad and no secondary trans cooler.  So far (25k miles) it seems to be okay.  No strange behavior, no weird smells, no dark fluid on the stick.  It's been in parades, long highway trips, ambient temps well over 100 and well below 50.  But, it's not handling 400 HP and lots of hard use.  It does pull the Heap over an 11,000 foot pass from time to time but the Heap is a thousand pounds lighter than the Town Car it came out of which also had no separate trans cooler.

So...there ya go.

BB

This is how my AOD is hooked up. Disregard the old rad and fan, those are gone. It is a two pass horazontal.
 I bipassed the trans cooler in the new aluminum rad and this is what works for me
https://imgur.com/a/9YZUX
https://imgur.com/58XhV0u

Last edited by Rudi (11/18/2017 1:47 PM)

Ideally you'd have a trans fluid temp gauge.  The determining factor in whether or not you need an auxiliary cooler is whether or not the trans ever gets hot.  Ideally you want the fluid in the 180 degree range at most.  Newer vehicles have sensors from the factory, and even if they don't have a gauge you can read the temp via a scan tool. 

Its rare for a car to need a cooler, but red351's comment about stall speed is well taken.  If your cruise RPM is lower than the converter's stall speed you really should have a cooler if you go on long cruises.  In such a situation there is more slip in the system than there should be, and that equals heat. 

IF, he goes with a lockup converter.  I certainly would, and its a point worth making.  Lockup converters always command a peremium and its tempting to ditch the lockup to save cost on an aftermarket converter.  Also, if your cruise RPM will be higher than the stall speed there's effectively no reason to run a lockup.  I don't run one in my K5 Blazer because my highway cruise RPM is higher than the stall speed of my converter.  This saved cost on the converter and eliminated a potential failure point.  That's also a fairly radical truck I've built (450HP N/A, 600HP on spray, big tires, 4.88 gears, but I built and kept my 700R4). 

Stock converters will all be lockup BTW, so if you're just reusing what the trans comes with its a non issue. 

Not surprising.  Most heat related transmission issues are from moving heavy loads, which a car just doesn't do.  Vehicles used to tow and plow are the ones that need to be careful.  Years ago you had to add coolers to trucks, but now it seems they all have them stock.  I've never seen the temp in my '06 F250 get above 160 no matter what I'm doing.