46RH transmission cooling

[Duodec]

Another question for future planning.  46RH transmission in my 318 A/C auto Challenger.  Generally the suggestion for cooling is to run fluid first to the cooler in the lower radiator tank, then to an external cooler, then back to the transmission. 

However the in tank cooler is set up for the stock 5/16" cooler lines, not the 3/8" recommended for the OD transmissions.  May only be the fittings but still a partial impediment to flow.

And however the in tank cooler is recommended because it helps the transmission fluid come to operating temperature faster, which is better for the transmission.  The radiator actually initially heats up the fluid before it starts

For those without the in-tank cooler, you just use an external and deal with the slower warm-up.

So, bad idea thread.  Would there be any benefit (re: warming up the fluid faster without losing flow) to running an external 3/8" cooler in parallel with the in tank cooler?  Tee off where the lines attach to the radiator cooler and run 3/8 to the external cooler.  That way you get the faster warm-up from the in tank cooler along with the increase capacity of the external cooler but with no restrictions to flow.

[MoparLeo]

If the engine is still carbureted, you will be warming the car up anyway.
 You can install and temp gauge for the transmission if you are concerned with temp.
Are you running a stock stall converter ?
If not, temp could be an issue.

[Katfish]

I'm in FL, so low temp is a non-issue.
I bypassed the radiator and only use a cooler.
What's the realistic low temp you'll see?
I assume the car is garaged, so outside temp would not be the determining factor on low operating temp.
ATF4 has a -50F pour temp, so I'd think anything you'll see won't bother it.
The manufacturers have to design for the worst of the worst, I'm guessing your car won't see that.

Heat is the real killer, that's why factory added an external cooler.

[Duodec]

Right now the car is immobile; I am just collecting info for the future.

Its a 318 2 barrel with A/C.  I don't know the level of impact of driving with cold fluid on wear, just have read a number of articles pointing out that a Torqueflite has a 'happy zone' for operating fluid temperature, and that wear is higher when the temp is low as well as too high, function improves and getting the fluid to operating temp quickly is a good thing and a valid reason for the cooler in the radiator.

As I remember, it has been many years, the car didn't take much engine/carb warmup before being quite drivable, certainly before the thermostat opened.  So driving with cold fluid, but that was in Las Vegas.  I drove it in 18 degree (f) up to 120 degree ambient and don't recall having issues at either extreme (though I did replace the radiator and chose one with more cores when I did).  the A904 trans never had an auxiliary cooler but it wasn't the original; I bought the car with the transmission malfunctioning and paid for a reman to replace it (which is still in the car 40+ years later).

     I'm assuming splitting the fluid flow across two paths will act somewhat like splitting current flow through two wires, one larger than the other.  Overall flow is not reduced, the smaller in tank cooler connections will mean more fluid flows through the 3/8" (or larger) external cooler, but with the head added from the radiator helping get the fluid to temp faster than just transmission operation would. 

Just looking for a bet of both worlds.  I do hope to drive the car on longer road trips; it might even be a daily driver once I'm retired and I certainly want to see how it does on a drag strip but that won't be a regular thing.  I don't know yet where we'll be other than not in ill-anoy and probably not the desert southwest...