Do Transmission Fluid Additives Work?

Walk the aisles of most auto parts stores and you’ll find multiple “mechanic-in-a-bottle” transmission additives that claim to restore transmission performance. Do transmission additives work? That’s what we’ll look at in this post.

Some transmission additives make lofty claims, promising one or more of the following benefits:

• Frees stuck valves to improve shifting
• Fixes transmission slipping
• Restores smooth shifts
• Stops leaks
• Conditions worn seals

What do transmission additives do?

First, let’s talk about what transmission additives are and what they do.

Your transmission fluid serves a few vital roles. It acts as a hydraulic fluid to enable shifting, protects gears and bearings against wear, manages heat and provides frictional properties to ensure smooth, consistent shifts.

Over time, the fluid deteriorates, especially if the transmission gets extremely hot from towing or hauling.

Towing and hauling stress transmission fluid.

Heat causes transmission fluid to oxidize, or break down. Fluids that break down allow sludge to form, which plugs narrow passages and interferes with shifting. Worn fluid can also fail to provide the correct frictional properties for your transmission. Eventually, you notice your vehicle shifting hard or erratically. Over time, the seals can also harden, causing them to crack and leak.

Transmission fluid additives are designed to restore the fluid’s properties responsible for providing the correct frictional properties, heat resistance and other benefits. Some include additives designed to soften and swell worn seals, purportedly “fixing” leaks.

They offer the advantage of costing less money than a fluid flush or refill. And, let’s face it, most people would rather dump a bottle of additive into their transmission in the Napa parking lot than schedule a transmission fluid service at their mechanic.

The problem, however, is transmission fluid additives don’t work very well

Although they may provide a short period of improved performance, transmission performance can become worse over time.

“Test data has shown some additives can provide a brief improvement in, for example, anti-shudder durability, but it’s short-lived and performance quickly drops below industry standards,” said mechanical engineer Matt Erickson, AMSOIL V.P. of Product Development.

Wear protection follows the same trend. “In one case, a fluid treated with an aftermarket additive actually offered worse wear protection than the untreated fluid,” said Erickson.

Cold-flow properties can also suffer, leading to delayed, elongated shifts on cold mornings. Transmission fluid that doesn’t flow quickly at startup can reduce protection, leading to increased wear.

Additives can harm your transmission

The fact is, lubricant manufacturers work hard to formulate transmission fluids that deliver reliable shifts while guarding against wear and leaks. Aftermarket additives can disrupt the fluid’s finely tuned chemical balance and degrade performance. Plus, most vehicle and transmission manufacturers warn against using them.

If you’re experiencing transmission problems, don’t waste your money on a “miracle” solution in a bottle. Visit your mechanic and have the problem fixed. Then, invest the money into servicing your transmission properly with a high-quality transmission fluid. You’ll likely save time and frustration in the long run.

Updated. Originally published Sept. 21, 2016.


  1. The AMSOIL Engine and Transmission Flush is a very EFFECTIVE product. My daughter had some hard shifting issues with her 2007 Ford Edge. I had suggested that she change transmission fluid but to first use the ATEF. She commented to to me how her transmission shifted so much better after the fluid dump. The shop that did the work commented how they were amazed about how much clumpy black fluid came out. Great product!

    1. Hi Jon,

      Thanks for the feedback; we’re glad to hear our product helped solve the issues with the transmission in your daughter’s Edge.


  2. I did a flush on my 2015 Subaru Forester using AMSOIL CVT Fluid. I did three 2 liter flushes into a soda bottle connected to the cooler hose, and used a laser thermometer gun to set the level at 107 degrees. It works fine now. Was at 110k miles on original fluid. Used two gallon garden fluid pump to refill. Videos show how to do it on YouTube. I am a P.C.

  3. Hi, How does the transmission cleaner work? Isn’t considered as harmful as remedy additives?
    My car is Nissan Sunny 1600cc AT 2013.
    Thank you.

    1. Hi Yahia,

      AMSOIL Engine and Transmission Flush uses a formula of light base oil technology, powerful detergents and dispersants to provide safe cleaning action. It dissolves and disperses sludge, varnish and deposits in both engines and automatic transmissions. Due to its detergent-based formulation, it can be easily disposed of with waste oil, making it more user-friendly. It’s perfectly safe to use.



  4. Additives used in the car plays an important role and lack of such additive could induce irreparable damages to the car. So, signs which warn that the lubricant level is reducing should not be ignored. The reason behind the reduction of the transmission fluid should be identified and repaired immediately to prevent any major mechanical abnormalities. So, the level of different types of additives used in the car should be inspected regularly and if necessary should be replaced immediately with suitable substitutes.

    1. Hi Hamidy,

      To offer a specific recommendation, we need more info about your vehicle. Contact AMSOIL Technical Services at [email protected] or 715-399-TECH.



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