Most drivers know that regular oil changes are important for keeping their vehicles performing at their peak, but many people neglect their transmission. Transmission fluid isn’t changed on a regular interval like engine oil and a proper transmission flush is far more expensive than your average oil change. Also, a transmission fluid flush requires a costly machine that prevents most owners from changing the fluid themselves. As a result, many drivers forget to service the transmission fluid with any regularity, while some others avoid the process due to the cost.

The problem with the approach of ignoring the need for fresh transmission fluid is similar to that of not changing your engine oil. Over time, the transmission fluid breaks down and it doesn’t lubricate as well. This leads to increased wear on the internal workings of the transmission. As the fluid breaks down and the parts begin to wear at an accelerated level, the fluid gets dirtier and that causes even more wear.

Fortunately, there is a myriad of products on the market that can help to prolong the life of your transmission and your transmission fluid. These transmission fluid additives improve lubrication, remove unwanted dirt deposits, and refresh seals, but with so many on the market, which do you choose? Here, we’ll give our recommendations for the best transmission fluid additives, as well as go into detail on what it is and why you might need it.

For more information on the best transmission fluid additives, refer to our table of contents.

1. Editor's Pick: Lucas Transmission Fix

lucas transmission fix

Lucas is a long-time leader in the world of engine oil additives, so it should come as no surprise that the company also provides a top transmission fluid additive. Lucas Transmission Fix is one of the products that does it all, just by adding the thick fluid to your transmission fluid. You do not need to drain any transmission fluid from your vehicle—you simply add the Lucas product to the current transmission fluid and let it work its magic.

The primary function of Lucas Transmission Fix is to prevent slipping, hesitation, and rough shifts. It does this by providing a thick, protective coating of all of the components. The thick fluid lubricates the inner workings of the transmission valve body, improving shift quality. The Lucas product also refreshes the shift bands, helping to prevent slippage under power.

This recommendation also helps to protect the moving parts of your transmission while helping to stop fluid leaks. Transmission fluid is thinner than motor oil and as it breaks down, it gets even thinner. As a result, it drains down quickly when the vehicle is not running, leading to metal-to-metal contact on start-up. The Lucas Transmission Fix prevents the lubrication from draining down, protecting the metal surfaces on start-up. Also, this transmission additive brings worn gaskets and seals to life, helping to prevent leaks.

2. Marvel Mystery Oil

marevl mystery oil

Marvel Mystery Oil, dubbed “the original oil enhancer and fuel additive,” can also benefit your automatic transmission. When added to your transmission, the product begins by clearing out sludge and other debris in the lubrication system. The sludge in your transmission causes portions of the valve body not to work properly. When the valve body isn’t working correctly, you are prone to experience rough or sluggish shifts. Of course, depending on where the unwanted deposits are located, the flow of transmission fluid can be altered, leading to accelerated wear and costly damage.

Once the Marvel Mystery Oil has cleared out the deposits of dirt and other debris, your valve body bits can move as planned and the transmission fluid will flow smoothly, reducing friction and heat. It then bonds to the internal surfaces, providing a layer of protection against more unwanted build-up going forward. This also reduces friction and heat, ensuring that your transmission will work properly for a longer period of time.

The key advantage of Marvel Mystery Oil is that you can also use it in your engine oil, fuel system, or power steering system. It offers the same advantages in the engine oil and power steering fluid while working as an excellent fuel system cleaner.

3. Bar’s Leaks Transmission Repair

bar's leaks transmission repair

Bar’s Leaks Transmission Repair comes from one of the largest brands of automotive additives. Bar’s Leaks has been around for ages, and it offers a product to help in just about every fluid on your vehicle. Like several of its products, this transmission additive is packaged in a two-in-one design. In one side of the bottle is a product that is promised to restore performance. In the other side of the split bottle, it states that it will add protection.

To restore performance, the Bar’s Leak transmission additive cleans out the valve body and the areas around the gears. This allows for proper fluid flow, preventing hard shifts and slipping. It also improves the condition of the shift bands, along with the various gaskets and seals. In fact, the bottle guarantees that this product will stop leaks, which makes sense from a brand known for stopping leaks. They offer all sorts of products because they are proven to work well.

In the other half of the bottle is a fluid that stabilizes the existing transmission fluid while coating all of the moving parts. This protective layer helps to reduce friction and heat, improving performance and adding to the life of your transmission. It will also help to prevent the transmission fluid from breaking down as quickly, although nothing is a complete replacement for periodic transmission service.

4. Sea Foam Trans Tune

seam foam trans tune

Sea Foam is a well-known fix for a rough-running engine, but the company can also help with transmission troubles. If you are concerned that your transmission isn’t shifting properly and your fluid is beginning to look dirty, Sea Foam Trans Tune may be the way to go. This product begins by loosening any debris build-up in the valve body and gear area. A cleaner valve body leads to smoother shifts and less hang-ups between gears. The Sea Foam also cleans and conditions the transmission fluid, breaking up any accumulated debris while also removing moisture from the system.

Sea Foam Trans Tune can be used in one of two ways. If you are getting ready to have your transmission flushed, you can add this product to the fluid a hundred miles before having the service done. If your key concern is clearing out the system, this is the route that you want to go. The Sea Foam will loosen up all of the crud in your transmission, making the flush procedure move effective.

You can then add a bottle of Sea Foam with the new fluid, helping to protect your transmission into the future by keeping debris from accumulating.

5. Prolong Super Lubricants Transmission Treatment

prolong super lubricants transmission treatment

If you have a new vehicle and you want to extend the life of your transmission by protecting the internals, Prolong Super Lubricants Transmission Treatment might be your best bet. The Prolong brand focuses on coating the metal surfaces with a special chemical compound that protects from both friction and heat at the molecular level. In other words, it coats everything in your transmission with a super-fine layer that prevents metal-to-metal contact while also allowing for a smooth surface during operation.

The Prolong Transmission Treatment isn’t a system cleaner, but if you have an older vehicle, this product is ideal for use right after a transmission flush with a proper cleaning product. It can also be used in both automatic and manual transmissions, so no matter what you drive, new or used, the Prolong transmission additive can help protect the moving parts of your gearbox from regular wear and tear.

While protection is the key concern, the Prolong Super Lubricants Transmission Treatment also improves performance. Your manual transmission will shift more smoothly and your automatic transmission will be more responsive and deliver crisper, more consistent shifts.

Transmission Additives: Everything You Need to Know

best transmission fluid additives

Photo credit: Standret /

Whenever you drive your vehicle, the transmission fluid is diminished in two key ways. First, even with proper lubrication, the natural friction between internal components wears down every moving part. As those parts break down, microscopic debris is mixed into the transmission fluid, which is what causes the majority of fluid discoloration. Also, as fluid wears out and breaks down, the fluid loses its ability to properly lubricate and disperse heat. As the fluid gets hotter, it breaks down more, leading to less protection of the metal surfaces and increased wear.

In addition to making the fluid dirty, the debris created by heat and friction of internal transmission components leads to deposits at crucial points. When this debris collects in the valve body, the valves cannot open and close normally, leading to sluggish shifts or the transmission hanging between gears. In other areas, the accumulation of this debris can cause an irregular flow of transmission fluid, and that can lead to dramatic failures when parts run dry.

Transmission fluid additives can help to prevent the accumulation of this debris in a variety of ways. Some products coat the surfaces, improving lubrication and reducing wear caused by metal-to-metal contact. Other products help to break up deposits of debris, both those which are stuck to parts of the transmission and the chunks moving with the fluid. Some products work as both cleansers and long-term protectants, but transmission additives don’t just improve performance and protect the moving parts.

In many cases, the first transmission problem that you will encounter in an older vehicle is a fluid leak. Sometimes these leaks are as simple as a transmission pan gasket that has gotten old and hard, which is usually a pretty simple fix. However, if there’s a leak at some other point on the transmission, the repair could be costly and time consuming. Before you pay a transmission shop to diagnose and fix a fluid leak, one of our recommendations intended to stop leaks is a good starting point. These products rejuvenate the various gaskets and seals around the transmission, helping to prevent leaks by simply adding the additive to the transmission fluid.

Some products focus on certain features mentioned above while others do it all. In most cases, products designed specifically to stop leaks or improve transmission shifts will do a better job than an all-in-one product, so make sure to find the product that best solves your problem.


Recent Updates

March 25, 2021: Updated with a promoted product recommendation.

We are committed to finding, researching, and recommending the best products. We earn commissions from purchases you make using the retail links in our product reviews. Learn more about how this works.

Main photo credit: EmiliaUngur /