According to former Indy car mechanic Dave Bowman, regular fluid and filter changes are vital to keeping automatic transmissions trouble free. Now employed as a vehicle-care expert for Allied Aftermarket Division (suppliers of Fram, Bendix, and Autolite parts), Bowman says that ideally the fluid and filter in the transmission should be changed every two years or 24,000 miles, particularly if the vehicle is over five years old. However, Bowman and other vehicle experts warn that by-the-book service is not adequate if you drive hard, tow a trailer, go off-road, or carry a camper. Under these “severe use” conditions, changing the fluid and filter every 12 months or 12,000 miles is critical as dirt and moisture buildup in the fluid can cause internal damage to an automatic transmission. Heat buildup can also be a problem. The harder the transmission works, the hotter the fluid gets. Even if your pikcup or SUV already has a towing package that includes a transmission cooler, having a second is just good insurance for those that live in the Deep South. The ideal operating temperature for ATF fluid is between 175 and 225 degrees Fahrenheit; towing in the heat of summer or tackling long grades can take those temps well beyond the safety zone. And when that happens, a good day turns bad.
It gets worse as temps continue to climb. Transmission plates start slipping at 295 degrees, and once the fluid temperature tops 300 degrees, the seals and clutches burn out and carbon forms in the oil. Complete transmission failure at this point is just a few miles away. In addition to checking transmission fluid levels frequently and having regular fluid and filter changes, the installation of an automatic transmission fluid cooler can go a long way towards increasing transmission life because it helps keep fluid temperatures out of the danger zone. Transmission engineers and cooling specialists say that a 20-degree drop in fluid temperature can doubles an automatc transmission’s life. This is especially important if you tow or carry heavy loads.
Even with the addition of a heavy-duty cooler, fluid temperatures can rise to dangerous conditions under certain conditions, such as when towing a heavy trailer up hills during the summer. That’s why it is important to keep an eye on transmission fluid temperature while you are driving, which means that the installation of a transmission temperature gauge is a vital part of making sure your transmission stays healthy. If you notice fluid temperatures are rising, pull over and let the transmission cool down before it reaches the danger zone. Just make sure that when you pull over, you put the transmission in Park, set the brake and let the vehicle idle for a bit, so the fluid circulates through the system as it cools down. Don’t shut the engine off because this will allow “heat sinking” of the fluid to occur, which can spike fluid temperature and cause the very internal oil cooking and parts damage you were trying to avoid.—Peter duPre |
Here is
an example of how heat kills: At 240 degrees, harmful
varnishes begin to form on internal transmission
components, at 260 degrees the seals harden and leakage
can occur as the hardening seals crack and break apart. 
You might think that
by having a transmission cooler installed and by
performing regular preventive maintenance on the tranny
that your transmission worries are over. Not So.