The Best Transmission Fluids to Keep Your Car Shifting Smoothly

Valvoline is one of the world’s best-known makers of automotive lubricants, so you know you can trust its automatic transmission fluid (ATF) to keep your vehicle working well. The product we’ve highlighted here is Valvoline’s Dex/Merc formulation, which will work in many General Motors, Ford, and import models with an automatic transmission designed for use with Dexron or Mercon lubricants. If this particular fluid isn’t recommended for your vehicle, don’t worry: Valvoline makes transmission fluids for nearly every modern vehicle, including those with manual transmissions, so you should be able to find one suited to your car or truck.

This friction-modified transmission fluid starts with a premium base lubricant and is fortified with additives to stand up to whatever driving conditions you can think of. Valvoline says its Dex/Merc ATF promotes smooth shift performance in your vehicle’s automatic transmission, as well as excellent friction stability for consistent shift quality.

This transmission fluid also promises protection against high-temperature breakdown, which means you can trust it to provide good lubrication if you regularly use your vehicle to tow a trailer. This fluid is formulated to flow well at low temperatures too, so your transmission will perform as it should even in cold winter weather.

Like any mechanical component, an automatic transmission will wear out over time, and you will eventually be forced to decide having it rebuilt or replaced, or bite the bullet and buy a newer vehicle. But in many cases, you can extend the life of a transmission showing signs of old age with an additive like Lucas Transmission Fix.

You don’t have to drain and refill your automatic transmission’s existing fluid to use this additive; you can simply add some of this product to the fluid in your transmission. However, if your transmission is already filled to the correct level, it’s recommended that you drain a small amount to prevent overfilling before adding Lucas’s solution.

Lucas says its Transmission Fix additive will help smooth out rough shifting and refreshes an automatic transmission’s clutch bands to eliminate slipping when the car is in gear. If your vehicle’s transmission is leaking fluid, Lucas Transmission Fix can also help by reviving the old, dried out rubber seals. The company also says you can use Transmission Fix in manual transmissions to reduce shift effort and extend the life of the gearbox.

The dual-clutch transmission (DCT) is a relatively new technology found mostly in high-end sporty vehicles, so you won’t be surprised that Triax’s Transyn synthetic lubricant is compatible with the DCTs used even in the Bugatti Veyron and the Ferrari 488 GTB. However, Transyn is also meant to do the job in the comparatively mainstream Ford Focus economy car, as well as models from Audi, BMW, Mercedes-Benz, and Porsche.

Triax Transyn is formulated to meet a DCT’s specific lubrication needs. That’s an important point, because the inner workings of a dual-clutch transmission are much different than those of a traditional automatic. Triax’s transmission fluid boasts low-friction chemistry to support the quick, smooth shifts that dual-clutch transmissions are known for. It also helps reduce wear and tear on the transmission’s gear sets. According to the company’s specifications, Transyn remains fluid at temperatures down to minus 60-degrees Fahrenheit.

Once you replace your dual-clutch transmission’s fluid with Triax’s Transyn, you shouldn’t have to change it again for at least 300,000 miles—which is to say it’s unlikely you’ll need to do so again as long as you own the vehicle.

Here’s a lubricant from another well-known brand that promises great protection for your vehicle’s transmission. Unlike the Valvoline product we named our Editor’s Pick, Castrol’s Transmax line of fluids is only for automatic transmissions and doesn’t include a formulation for manual transmission vehicles. This recommendation is formulated to meet the requirements of automatic transmissions designed for Dexron and Mercon lubricants. That makes it suitable for a vast number of vehicles, especially the Ford and GM vehicles for which those two lubricant types were created.

You can also buy Castrol Transmax fluid for imports, Chrysler vehicles, and cars and trucks that use a continuously variable transmission (CVT) instead of a traditional step-type transmission. If your vehicle has high mileage, Castrol also makes a special version of Transmax with additives to help with rough shifting and leaks typical in older cars and trucks.

Transmax boasts a low-viscosity formula that Castrol says will help boost your vehicle’s fuel economy. Enhanced friction durability ensures smooth shifting performance in your transmission, along with high-temperature protection for both city and highway driving, while oxidation resistance helps avoid viscosity increases that can degrade transmission performance and service life.

The final entry in our list of the best transmission fluids is Hot Shot’s Secret Shift Restore. Unlike Lucas’s Transmission Fix, this product’s focus is preserving performance and reducing wear and tear in your vehicle’s transmission rather than improving the function of a worn-out unit. However, Hot Shot’s Secret says Shift Restore will also address some of your most common transmission performance complaints, like inconsistent shift quality.

Hot Shot’s Secret Shift Restore’s main claim is that it reduces the formation of gum and varnish deposits that can build up over time in your transmission and cause poor shifting. It can also dissolve existing deposits, which can be the root cause of driveability problems including hesitation, rough or noisy operation, and overheating.

Shift Restore’s other trick is its ability to coat your transmission’s metal components to provide an extra layer of lubrication and protection against metal-on-metal wear. A by-product of that is a promised reduction in operating temperature, which helps extend the life of friction components like the clutch bands that allow the transmission to drive the car.

How often do you need to change the transmission fluid in your vehicle?

Can you change your car or truck’s transmission fluid yourself?

Should you use synthetic transmission fluid?

This is up to you. Synthetic transmission fluid is made to last longer than conventional types, so you can go longer between fluid changes without sacrificing quality lubrication. However, synthetic oil costs more, so we recommend you do the math to see which type of transmission fluid will cost you less over the life of your vehicle.

Are transmission fluid additives safe to use in your vehicle?

Yes, they should be safe to use without fear of damaging your vehicle. However, if a fluid is not specifically recommended by the company that made your vehicle, using it could void the warranty if your car or truck exhibits transmission problems.

Your best bet is to talk to your mechanic or dealership service department to ask what they think about a particular additive and whether it could help or hinder your vehicle’s performance.

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