Transmission Leak

5 Best Additives to Stop a Transmission Leak

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Transmission Leak

If you’re looking to stop a transmission leak in your vehicle, you’ve come to the right place!

Chances are if you asked a person what the most important part of a vehicle is, nine times out of ten they will probably say the engine. While the engine may be the powerhouse for your vehicle, keep in mind that power also has to get to your wheels! This is done through your transmission. Without a transmission, your vehicle would be just as useless as if it didn’t have an engine. Unless, of course, you didn’t actually need to drive your vehicle. We’re here to help you protect your investment and identify a product to stop a transmission leak if one has been spotted.

Why is it Important to Stop My Leaking Transmission?

While a leak in your transmission may sound like nothing more than a nuisance, a leaking transmission could lead to much larger issues. Even if the leak is slow, low fluid over time or forgetting to fill it could mean damaging the components inside. This might not be something noticeable at first as the internal parts will wear slowly. Once the parts have worn down, there is no turning back. The transmission will eventually function improperly and have mechanical damage. Transmission leak causes are generally seal breakdown over time and use. It’s important to stop a transmission leak before this damage occurs.

If left too long with low or no fluid, your vehicles transmission is at risk of being destroyed to the point where the vehicle will not function properly, or possibly not even drive. If left to this point the only option will be to repair the transmission. This is not only inconvenient, but could be very expensive as well. On top of all the cost and downtime, leaking fluid is also bad for the environment and will stain your driveway as it sits. While transmission leak repair can be expensive, many times you can stop the leak with a simple additive. In the big picture, it’s cheaper and easier to stop a transmission leak instead of letting it get damaged further.

If you’re wondering if you can add fluid to your vehicles automatic transmission yourself, check out our guide Easy How to: Check Automatic Transmission Fluid Level to see if your vehicle applies. You’ll see how simple it is to add fluid to your transmission and will be well on your way to stop a transmission leak!

Transmission Leak Fix Product Guide

In this guide we cover a few options so you can choose the best additive to stop a transmission leak. While you should always keep an eye on your transmission and perform proper fixes and maintenance, we understand it’s not always practical to do this right away. That’s why we put together a few products that will hopefully help you until you can get your vehicle properly checked. Some additives will even help condition your transmissions parts to help prevent leaks in the future! Future prevention means no need to stop a transmission leak later. Check them out below!

1. Lucas Transmission Fix

Slipping Tranny

Lucas is a common name amongst the auto scene and we’re here to show you yet another impressive product they have come out with. If you’re looking for the best for your transmission, look no further than the Lucas Transmission Fix. Not only will this eliminate leaking seals, there are a handful of items Transmission fix will help with as well:

  • Eliminates seal leaks
  • Cleans and lubricates internal valves
  • Lowers operating temperatures to reduce foaming
  • Prevents slipping

Dosage Guide For Lucas Transmission Fix

The standard size Lucas Transmission Fix is offered in a 24 ounce bottle. It’s recommended to add one bottle to a standard transmission. For larger or worn transmissions, a second bottle may need to be added. Finally, for sub compact vehicles, it’s recommended to add 12 ounces. Results can be seen almost immediately after adding, and it’s recommended by Lucas to add Transmission Fix with every fluid change, typically in 30,000 mile increments.


2. BlueDevil Transmission Sealer

Transmission stop leak

If you’re looking for a product to stop just about any kind of leak, you’ve probably heard of Blue Devil. Blue Devil has been in the business of stopping leaks since 1997 and has had plenty of experience doing so over the years. As with a lot of problem areas, they’ve designed a product to help stop leaks in transmissions as well in their Blue Devil Transmission Sealer. With one main goal in mind, this product is easy to sum up:

  • Restores dried, cracked, and shrunken seals
  • Works for both manual and automatic transmissions

Dosage Guide for Blue Devil Transmission Sealer

The standard size bottle of Blue Devil Transmission Sealer is 16 ounces.

  • 1 ounce treats 1 quart of transmission fluid

There’s not much to know about using this transmission sealer as it’s extremely easy. Simply locate your transmission’s dipstick and add it to the existing fluid! The only thing you need to know is the capacity of your vehicle’s transmission as it’s important that you do not overfill the fluid. If your vehicle is equipped with a dipstick on the transmission, you don’t even need to know the capacity, just monitor as you add the sealer. Note that some existing fluid may need to be removed if the system is currently topped off.


3. No Leak Transmission Stop Leak

How to stop a transmission leak

No Leak Transmission Stop Leak is another excellent product produced by Gold Eagle. This product is not only focused on stopping leaks in your vehicles transmission but has a few extra tricks up its sleeve as well. No Leak is safe to use with all transmission fluids and is as easy as simply adding to the existing fluid in the transmission. A few notable items No Leak is capable of doing:

Preventing as well as stopping existing transmission leaks
Helps reduce hard shifting
Swells, softens, and conditions damaged seals
Safe to use with all transmission fluids

Dosage Guide for No Leak Transmission Stop Leak

The standard size of No Leak Transmission Stop Leak comes in a 16 ounce bottle.

  • One bottle of Transmission Stop Leak treats one transmission

Adding No Leak Transmission Stop Leak to your vehicles transmission is just as simple as adding the others. Simply locate your transmission’s dipstick and add it to the existing fluid! The only thing you need to know is the capacity of your vehicle’s transmission as it’s important that you do not overfill the fluid. If your vehicle is equipped with a dipstick on the transmission, you don’t even need to know the capacity, just monitor as you add the sealer. Note that some existing fluid may need to be removed if the system is currently topped off.


4. ATP AT-205 RE-SEAL

How to fix a power steering leak

ATP Automotive has designed a product that helps with restoring seals, gaskets, and reducing leaks in many applications. Not only can AT-205 RE-SEAL help stop leaks in your vehicles transmission, it can be used in other applications from power steering, to hydraulic systems, to engine oil. This makes this product extremely versatile which is a must have around the garage. If you don’t use it all the first time, there is sure to be some additional uses for it down the road. Below are a few notable features of AT-205 RE-SEAL:

  • Helps restore worn or dried out seals
  • Will not harm bearings or other components
  • Can be used in transmissions, engines, power steering, differentials, and hydraulic systems
  • Formulated to keep from over-swelling or breaking down seals

Dosage Guide For ATP AT-205 RE-SEAL

The standard size of ATP AT-205 RE-SEAL is an 8oz bottle.

  • One 8oz bottle will treat 6 quarts of fluid

If your transmission contains more than 6 quarts of transmission fluid, it’s recommended to add additional fluid to get the maximum effect out of AT-205 RE-SEAL. As with all transmission additives, it’s important not to overfill your vehicles transmission with fluid. If your vehicle is equipped with a dipstick on the transmission, you don’t even need to know the capacity, just monitor as you add the sealer. Note that some existing fluid may need to be removed if the system is currently topped off.


5. Bar’s Leaks Transmission Stop Leak

Best additive to stop a transmission leak

Bar’s Leaks is another well known brand that specializes in building additives specifically for stopping leaks. They are in the market for all kinds of equipment from cars, commercial trucks, lawn equipment and even marine applications. Being so involved with a wide variety of equipment, they understand how important it is for the end users. This especially means understanding how critical it can be for your transmission to keep proper fluid levels.

Your vehicle needs to stay reliable and be able to get you from point A to point B without any issues. One of their star products, Transmission Stop Leak, is designed to stop a transmission leak and help ensure it holds its fluids and won’t leave you stranded. Below are a few stand out attributes of Transmission Stop Leak:

  • Stops leaks at seals and gaskets
  • Typically fixes leaks in 200 miles
  • Works in both automatic and manual transmissions

Dosage Guide for Bar’s Leaks Transmission Stop Leak

The standard size for Transmission stop leak is an 11 ounce bottle.

  • One bottle of Transmission Stop Leak treats one transmission

Just like the other additives, simply locate your transmission’s dipstick and add it to the existing fluid! The only thing you need to know is the capacity of your vehicle’s transmission as it’s important that you do not overfill the fluid. If your vehicle is equipped with a dipstick on the transmission, you don’t even need to know the capacity, just monitor as you add the sealer. Note that some existing fluid may need to be removed if the system is currently topped off.

Per Bar’s Leaks, this additive will usually stop a transmission leak after 200 miles or 3 days or driving. the leak should be monitored and if it continues, a second application should be applied.


Final Thoughts


There are many things that can cause a transmission to leak, a simple additive should be your first step in repairing a transmission leak. Whether you’re simply looking to stop a transmission leak, or give your vehicles transmission some extra care, we hope this guide has been helpful for you. Whatever you pick, just make sure you don’t leave your leak untreated for too long. The last thing you want is for your transmission to leave you stranded and your wallet empty!

3 thoughts on “5 Best Additives to Stop a Transmission Leak”

  1. Very helpful and informative when it comes to knowing how to stop transmission leaks or any leaks for that matter.

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