Quote:
Originally Posted by Jesse Z
I've always assumed that the big finned auxiliary coolers are more efficient than the in-radiator types, if for no other reason than they are farther away from the heat of the radiator and engine.
If in doubt you can run lines to BOTH your radiator cooler and auxiliary cooler in series, like so:
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there are two reasons to use a rad mounted cooler over an external cooler.
1. heat transfer by conduction (by contact) is much more efficient than convection (by air movement), and is not subject to changes in efficiency by variation in the air (temperature, humidity, airflow speed, etc). this is why rad mounted coolers can be so small in the tank, the contact of the coolant with the cooler is very very efficient. a comparable external cooler will need to be much larger, even the efficient stacked plate types. the ability to reject heat through the radiator is also much much more efficient, meaning, a very hot trans will have a lot of cooling potential in a radiator mounted cooler system, the rad rejecting heat by convection, but the surface area of the rad is very very large, larger than an external trans cooler.
2. its true the radiator mounted cooler will never cool beyond the thermostat temperature (or final temperature) of the coolant, but the coolant will warm up much faster than the transmission fluid will, and so on cold days or even during a cold start the transmission fluid in a rad mounted cooler will warm up much faster than with an external cooler. if you have ever driven a cold trans, you know the benefit. external coolers sometimes have a waxstat to limit flow until warm
transmission damage is exponential as fluid temps rise over ~250 degrees. there is a lot of sense in running an external cooler WITH the rad cooler, especially when towing or climbing hills.
stay away from fin type or tube and fin coolers for an external cooler. stacked plates, also called plate type, maximize surface to air convection.