Trans temperature gauge

DougE wrote:
If you search some you will find most sources state that the design operating temperature of automatic transmissions is 175*. You will also find that most life vs. temperature charts for auto transmissions do not go below 175*. This is the reason behind installing an auxiliary cooler prior to the radiator cooler. This allows cool trans fluid to be warmed up to the correct temp as the outlet of the engine radiator is ~175*.

The engine radiator is NOT ~175°F. It usually is MUCH colder than that. Have you ever measured the temperature in the cold side of the radiator? I have, in ambient temperatures from -40°F to +115°F. When towing heavy in high ambients the temperature drop across the radiator can be as small as 15°F. But in cold weather, running lightly loaded the cold side of the radiator is within a few degrees of the ambient temperature. If it's 0°F outside you can expect the cold side of the radiator to be around 5-10°F. How well is THAT going to warm your ATF?

The correct routing for the ATF flow is from the trans to the radiator cooler, then to the aux cooler, then back to the trans. This is the way all of the auto companies route it because they understand how the system works.

But you are right, the designed operating temperature of the trans used to be about 175°F. It has moved higher in recent years to improve efficiency. Newer fluids and materials in the trans are designed to live at those temperatures.

Those charts that are floating around the internet that talk about trans death in feet instead of miles if the trans ever gets above 200°F are based on 1960's technology, or just flat out lies.