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. AMSOIL transmission oils give you all the information you need about all their fluids and what they can be used in. They will not list for your application if they feel it doesn’t work. Just make sure you choose the right fluid for your transmission. I used AMSOIL transmission oil to replace the WS oil in my Toyota Tacoma; a simple drain and fill at 30,000 miles because I was a little worried about the under-fill issue from the factory. The transmission didn’t have any issues; I just didn’t like that everyone was saying that 90 percent of the transmissions left the dealership under-filled just because it had to be hooked up to tech stream to do a fluid check and dealers didn’t do it unless you complained about shift-quality issues. Long story, but I did research on Toyota WS fluid and nothing is special about it besides it being a fuel-saving, thinner fluid Toyota decided to use. NO WAY IS IT A LIFETIME FLUID. Test shown from lab testing says it is not even synthetic, semi at best with wear additives and shutter-pack additive. I used AMSOIL universal fuel-saving transmission oil, which says it is safe for WS fluid applications. I see that AMSOIL transmission oil is 100 percent synthetic, has a higher temperature flashpoint and seems to have a much better anti-wear package than WS fluid. I couldn’t be happier with my decision to use it. I found out my transmission was 5.6 oz. low from factory. Followed the drain-and-fill process to the letter per Toyota check-and-fill procedure. Now, my transmission shifted just fine before change, so being low only 5.6 oz. didn’t affect the transmission shifting I don’t think. According to Toyota it shifted just as it should. Guess what though, now it shifts like a dream; gear changes are smooth as butter. I promise you will notice a difference. This was just a pan plug fill and change and I noticed a difference in the first half a mile driven. AMSOIL has changed my mind on a difference a good fluid can make. Just an extra note – my WS fluid was still pretty clean at 30,000 miles (80 percent highway miles). Not clean as new, but still able to see through it when held up in sunlight. Since this was just a slight fluid change mostly just to check condition of WS fluid at 30,000 miles and factory under-fill issue, I will be doing a pan drop and filter change at 60,000 miles. I will use the AMSOIL transmission oil instead of the Toyota WS. I would not of believed a fluid could make a difference like I have experienced. Do what I did and give AMSOIL a try. If you don’t like it you can always go back to WS fluid when you do a filter change. Please everyone check you Tacoma transmissions for low fluid. I have heard of them being a quart low from factory. Check even if you don’t use AMSOIL trans fluid to refill.

  2. 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.


  3. 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.

  4. 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.



  5. 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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