Should You Change Your Transmission Fluid?

June 9th, 2020 by

-The first automatic transmission was introduced in the Buick concept car in the late 30s, and in the post-WWII years, automatics became more and more common, especially in luxury brands such as Cadillac and Chrysler. Early automatics were derisively referred to as “slush boxes”- they were inefficient and slow, and tended to sap power and acceleration.
Automatics use automatic transmission fluid (ATF) and fluid couplings instead of a mechanical clutch disengaged by the driver. In other words, the ATF is pressurized and used to transfer the torque through the entire unit, as well as to cool and lubricate the rotating assemblies in the transmission.

In a modern vehicle with the most driving, performance and emission functions governed by the Engine Control Module (ECM), automatic transmissions have become far more complicated. They’re just as much an electronic device as a mechanical one, and although they’ve become more efficient and reliable, they’re a lot more expensive to service when something goes wrong.

One thing that is important to remember is that heat is the archenemy of your transmission and fluid. Even running 10 or 20 degrees above the recommended operating temperature of your manufacturer can quickly break down the fluid to a point where it loses its lubrication properties. Towing a trailer or transporting heavy loads will definitely stress the transmission and cause it to run hot, and the burnt or worn transmission fluid will put additional stress on the unit and may significantly shorten its lifespan.

The Different Kinds of ATF

It is useful to know that, in the last 20 years or so, automatic transmissions have become so specialized that many require their own fluid formulations. Each type of ATF has its own friction properties, detergents, anti-corrosion agents, seal and gasket conditioners, and other additives that are customized for specific transmission. Using the wrong brand or ATF formulation will quickly damage or even destroy the transmission. Here’s a partial rundown of some of the current ATF blends:

  • ATF +4: For Chrysler/Dodge/Jeep vehicles, replaces ATF+, ATF+2, ATF+3 formulations
  • DEXRON III/MERCON: Pre-2006 GM models, pre-2004 Toyota, Ford/Lincoln/Mercury, and others
  • DEXRON VI: Post-2006 GM models, some Fords, replaces Dexron III
  • MERCON V: Most Ford/Lincoln/Mercury, Mazda B-series trucks, Mazda Tribute
  • MERCON LV: Ford Duratec LE, Mazda Tribute
  • MERCON SP: Some Ford 6R transmissions (others use LV)
  • TOYOTA TYPE T-IV (aka T4): Some Toyota and Lexus models, replaces Type T, T-II, and T-III

So you see, there are quite a few different formulations of ATF now, each of which has its own specific properties. The correct fluid should be indicated on the transmission dipstick or in your owner’s manual.

How Often Should You Change Your Transmission Fluid

If you have a new vehicle, you should run the transmission fluid flush, change, and refill at a distance of about 40 km (check your manual for exact specification). If your vehicle is used regularly for heavy duty purposes, such as towing or transporting heavy loads, this interval should be shortened. Whenever the fluid is changed, the filter should also be changed (if your transmission has one) and the fluid should be inspected for metal shavings, plastic fragments and other signs of significant wear.

On a vehicle that has passed the 100k mile mark (especially if you bought it with a high mile mark on it), many technicians are now recommending that the fluid and filter should not be changed. If the fluid is old enough to be dark and has a burnt-toast smell, changing it may run the risk of dislodging sludge and varnish from the top to the torque converter. In such a case, these particles can make their way through the unit and the clog valves and other small passageways, leading to failure. However, this is something that should be addressed on a case-by-case basis and the decision should be taken by a qualified transmission technician.

Healthy ATF

  • Pinkish-magenta and translucent (almost clear)
  • Sweet-ish smell
  • A drop of ATF on a paper towel should be spread to about half a dollar, with no discolored spots
  • Remember to check the ATF level with the engine running and fully heated, the transmission in the park and the vehicle on the ground level.
  • Check your manual for specification, but a lot of people recommend that the fluid be warm but not hot.

If you decide to change your own transmission fluid, be aware that many units do not have a drain plug on the pan like the engine does. The fluid will drain after you’ve removed enough bolts from the pan, which means it’s going to be a messy job. Check the service manual for the bolt-tightening sequence and torque specifications when replacing the bolts for the pan. Do not over-tighten the bolts, as this may distort the edge of the pan and cause leakage. If you have more questions about your transmission fluid, or even want to learn about other topics like the difference between premium vs. regular gas, reach out to us today!

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