Most people know about fluids like motor oil and windshield washer solution and regularly check and replace them. But other fluids, such as brake fluid and (especially) transmission fluid fly under the radar. That’s a shame: Other than the engine, the transmission is the most vital component to the vehicle’s operation. If you don’t know how often to change transmission fluid or how to check it, read on for a rundown.
How often should transmission fluid be changed?
Many car owners don’t know how often to change transmission fluid, and the truth is that there’s no hard-and-fast answer. Different manufacturers use different formulations, and their maintenance intervals for how often you should change transmission fluid can vary from about 30,000 miles to… never. Some automakers have even introduced sealed automatic transmissions with no dipstick, no filler tube and lifetime transmission fluid.
There are a lot of reasons for that variance.
Is there a difference between manuals and automatics?
Manual transmissions need their gear oil changed over a vehicle’s life cycle, but they require a completely different type of oil from the kind used for automatic transmissions. A manual transmission’s design is fundamentally different, but their oil can still be prone to contamination by microscopic metal fragments that wear synchronizers, bearings and other parts. Manual transmissions should generally have their gear oil changed every 30,000-60,000 miles.
What is automatic transmission fluid?
Automatic transmission fluid (ATF) is as vital to your transmission as motor oil is to your engine. It lubricates and cools the transmission and prevents oxidation and corrosion, as well as transferring torque through the unit. Until the 1970s, transmission fluid actually contained whale oil as one of its ingredients. ATF contains additive packages, friction modifiers, anti-foaming additives, gasket conditioners, anti-corrosion agents, detergents and other ingredients custom-formulated to provide the best protection and reliability.
Unlike green antifreeze or honey-colored motor oil, ATF is dyed red to make it easy to identify. Without the fluid, your car’s transmission would overheat and self-destruct within a few minutes of operation.
Types of transmission fluid
There used to be only a few types of transmission fluid on the market: Type F for Ford vehicles, Type A, Dexron/Mercon for General Motors and Dexron II for GM and Chrysler models. Today, manufacturers and engineering teams have ATF formulations specific to their vehicles, including:
- ATF +4 (Chrysler, Jeep, Dodge)
- Mercon V (Ford products)
- Mercon LV (other Ford models, Mazdas)
- Dexron VI (GM, pre-2004 Toyota)
- Matic S, Matic K, Matic D (Nissan, Subaru, Infiniti)
- Toyota ATF-WS (post-2004 Toyota)
- ATF-TIV (Lexus, Volvo, VW, Audi, certain Toyota models)
- SP-IV (Hyundai, Kia, Mitsubishi)
No doubt this seems pretty confusing, but here’s the one thing you need to remember: Each of the variations listed above are designed specifically for those vehicles. Using the wrong variety of ATF in your transmission can cause serious damage or even destroy the unit in fairly short order. Make certain that you’re using the manufacturer’s recommended fluid—even if you take your vehicle to a shop for a flush and refill.
Why does transmission fluid need to be changed?
Motor oil degrades over time, picking up contaminants and losing its ability to lubricate. The same sort of thing happens with transmission fluid—it picks up microscopic metal shavings, some of which are caught in the filter, then loses its lubricating properties and leaves varnish-like deposits on internal assemblies, possibly clogging small passages inside the unit.
Heat in particular is the enemy of transmission fluid. The excess heat generated by towing a trailer or hauling a heavy load puts a huge amount of stress on your transmission and ATF, and will break the fluid down much faster. That’s why aftermarket transmission coolers are available for heavy hauling or towing. A transmission cooler looks like a small radiator and mounts up front for air flow, with a supply line and return line from the transmission circulating fluid through it.
Signs you need to change your transmission fluid
Regardless of manufacturer recommendations on how often you should change your transmission fluid, these are all signs of possible trouble:
- ATF darker in color, rather than the pinkish/magenta color of fresh fluid
- A distinct burnt-toast odor
- Delayed engagement putting the transmission in gear
- Delayed shifts from one gear to another
- Slippage when the engine races but the transmission isn’t really engaging properly
Some of these conditions can be the result of low transmission fluid levels. Burnt transmission fluid means you should get to a transmission shop for a flush and fluid and filter change as soon as possible.
How to make your transmission fluid last longer
You still need to have your fluid and filter changed at recommended intervals, which can vary by year, make and model according to manufacturer designs. To try and get more life out of your transmission:
- Regularly check the fluid. Many manufacturers recommend checking fluid with the engine idling and the transmission in park, while others require the engine to be off.
- Top off the transmission if the dipstick reads low.
- Keep an eye out for darker, burnt-looking fluid and the telltale burnt-toast smell.
- Go easy on acceleration and try to avoid towing or hauling extra-heavy loads.
- Always wait until the vehicle is completely stopped before shifting from reverse to drive or vice versa.
- Never rock a vehicle back and forth from reverse to drive to get out of mud or snow.
The transmission is the single most complex part of your vehicle—and one of the biggest expenses should something go wrong. The good news is with the right driving habits and the right maintenance, your automatic transmission should last through the entire life of your car or truck.