Transmission Temps: How Does Extreme Cold Affect Your Transmission

Some time ago, I put together an article that talked about how heat affects transmission fluid. It’s no surprise that getting this lubricator of gear changes hot has detrimental effects, but what we didn’t get into in that article was about transmission temps when it’s cold. While this might not be much of a concern in warmer southern climates, those of you in the north might want to hear about what the professionals at RevMax have to say about the subject.

Since transmission fluid does have an optimal temperature range for longevity, truck manufacturers have been incorporating thermal switches in the transmission fluid lines for several years to help the fluid warm up to this range. But enthusiasts have been removing these thermal switches for just about as long.

The reason, at some point, a couple of truck owners had an issue where this switch stuck in the closed position. When this occurs, the fluid is not allowed to circulate through the fluid cooler and this causes overheating issues. RevMax offers what is called a thermal bypass block that eliminates the problem-prone switch.

transmission temps

However, I got to wondering if the removal of the thermal switch could have adverse effects in severely cold climates. Since the thermal switch keeps the fluid circulating within the transmission and does not allow it to reach the fluid cooler until a certain temperature is reached, the absence of the switch could cause warm-up to take longer. Heck, without the switch, will transmission temps even get to optimal temperature in severe climates?

To get some answers, I reached out to Tom Hauser at RevMax to find out.

“From all of our research and real-world testing, the RevMax bypass block that eliminates the factory thermostatic valve has been nothing but a huge success. You bring up a great point about “optimal operating temps” but when we removed the thermostat, we have 100-percent, always on cooling.”

“When people say the word “optimal” are they talking about clutch holding power or economy? From what we have gathered from engineers, there are two main reasons for the factory thermostat. One is to get the truck up to operating temps faster, especially in cold climates.”

Tom continues, “the second reason comes about when you have thicker fluid. This will possibly decrease mileage (according to some government agencies) and this is what we feel they are talking about when they use the word optimal.”

Tom also told us that when RevMax speaks to customers who live in Canada, Alaska, or other regions with extremely cold climates, they do suggest that truck owners keep the thermostatic block installed. However, they also always suggest keeping an eye on transmission temps. The main reason to replace the factory thermostatic valve is to not cause the fluid to remain cooler than with the switch, the main reason is to eliminate the factory thermostat so that it is no longer in place and able to get stuck in the closed position and overheat your transmission. “If you remove this factory block you will never have to worry about it failing,” quips Tom.

transmission temps

Adding a thermal bypass will eliminate any chance of the thermal switch getting stuck close.

Something to keep in mind is synthetic fluids are not as susceptible to temperature extremes as traditional fluids and retain their given specs under cold weather conditions. What’s more, synthetic fluid has other advantages beyond temperature management.

According to AMSOIL, synthetic transmission fluid offers several benefits over conventional transmission fluid. These are improved wear protection, increased cleanliness, better heat resistance, and smoother cold-weather shifts. Synthetic transmission fluid doesn’t contain the impurities inherent to conventional fluids that are distilled from crude oil. Instead, synthetic uses base oils that are engineered in the lab.

This allows the fluid to contain only molecules that serve a designed purpose. As a result, synthetic transmission fluid delivers excellent wear protection to help your transmission last as designed, helps reduce heat to keep components clean, and flows readily in the cold.

Maybe including a thermal bypass switch and synthetic fluid is the right combination for your truck.

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About the author

Randy Bolig

Randy Bolig has been working on cars and has been involved in the hobby ever since he bought his first car when he was only 14 years old. His passion for performance got him noticed by many locals, and he began helping them modify their vehicles.
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