Re: Transmission Cooler Mounting FAQS

[Tom Jennings <tomj@xxxxxxx>]

On Sat, 25 Jun 2005, Bruce Hevner wrote:

> The auto trans gives off more heat than you think. Anyway that's my story
> and I'm stiiicckken to it.


Yeah, check this out!

The efficiency of an automatic transmission is pretty good;
somewhere in the upper 90's percentage-wise.

Horsepower NOT sent to the wheels becomes heat.


It's about 770 watts per horsepower if I recall. Here's chart
showing how much heat is produced:


           transmission efficiency 
HP  |      0.99 (1%) 0.98 (2%) 0.95 (5%)
------------------------------------
100 |        770      1540      3850 watts of heat
200 |       1540      3080      7700
300 |       2310      4620      11550
400 |       3080      6160      15400


As HP passes through the trans, 1% to 5% (anyone know numbers?) of
it turns to heat. 100HP engine power generates 770 watts of
transmission heat.

Put a 750 watt spaceheater inside a small metal enclosed box and
see how hot it gets. If there wasn't a safety switch, it would
reach 500, 600, 700 degrees in minutes. The spinning torque
converter dumps some heat, as does the cast body, the rest depends
on that cooler.

It's a miracle that auto transmissions work at all!

(Even a little Rambler with 100hp six doesn't really output 100hp
for very long, at highway cruise, it's what, 30? 40? hp? The
problem is the heat builds up in the transmission, even a 300 -
400 watt space heater locked in a metal box will get oven-hot.)

You could probably work out the difference in miles/gallon manual
vs. auto trans in terms of BTUs/mile and figure out the amount of
heat produced in the automatic transmission that way.