Automatic Transmission Cooler Testing and Development Part 3

With cooler weather rolling into Southern California this winter we noticed that the transmission temps were a bit cooler than we’d like to see with our transmission cooler installed. While we plumbed it so that the fluid goes from the transmission to our auxiliary cooler to the factory heat exchanger and back to the transmission, the factory heat exchanger can’t quite add enough heat back to the fluid to warm up sufficiently. In some cases of cruising on the highway in 40 degree weather we saw transmission fluid temps drop as low as 127 degrees at steady state. Considering that our initial testing indicated that the OEM engineers designed the system to run at higher temperatures (189 – 200 degrees) and viscosity is affected by temperature we started working on a thermostat option for people that drive their cars in cooler weather.  Here is a diagram of how the thermostat gets plumbed:

T-Stat Plumbing Diagram_Flat

We started by adding an off the shelf, inline thermostat rated at 180 degrees to the system. Initial testing showed that the thermostat actually started opening at 160 degrees. Since thermostats are generally rated by their opening temperature, we thought that was a little odd. After discussing with the manufacturer of the inline thermostat we opened up the housing to swap out to a higher temperature wax motor. Low and behold it was equipped with a 160 degree wax motor as the temperature was stamped onto the housing. Apparently, this is common practice with the oil thermostat manufacturers for some reason.

While we tracked down a suitable replacement wax motor rated at a higher temperature, we did a little long term testing with the 160 degree thermostat installed. It did help bring the temperatures up a little higher, but they were generally in the 158 – 163 degree range cruising on the highway and up in the 169 – 177 degree during extended street driving. Obviously, the transmission cooler is more effective at highway speeds at shedding heat.

We finally were able to source a 195 degree wax motor that works in the thermostat housing, installed it and started doing some testing. Steady state cruising on the highway is now closer to OEM at 170 – 180 degrees. While one would expect the temperature to be closer to the opening temperature of the thermostat, approximately 10% of the fluid flowing through the thermostat does go out to the cooler circuit when the thermostat is closed. This is to prevent thermal shock when the thermostat opens as well as keep the cooler circuit pressurized.

In addition, we did some quick track testing to verify that the thermostat does not adversely affect the cooling ability of the system. We were fortunate enough to get 4 runs in our session (1 more than when we did the initial track testing). We are happy to report that the transmission outlet temperature stabilized at 223 degrees at the end of the 3rd run and did not exceed that temperature during the 4th run.

In conclusion, we are now offering a thermostatic option as an add on for those who drive their cars in cooler weather and would like their transmission temperatures to be closer to stock when adding our cooler kit.  Now available for purchase from our web store here.