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Transmission Cooling Lines Leaking: What You Can Do

Transmission Cooling Lines Leaking

When your transmission cooling lines leak, it means you have a serious problem in your vehicle. Along with your engine, the transmission is arguably the most important part of your vehicle. If either the engine or the transmission fails, you no longer have a drivable car. That's why getting the transmission cooling lines fixed when a problem arises is key to maintaining a well-functioning vehicle. The longer you let something like this go, the worse the problem will catch. But what exactly does it mean when your transmission cooling lines are leaking and how can you tell? Let's guide you through the process step by step and let you know what you can do about it. 

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What is a transmission cooling line?


Your transmission cooling lines, often just called the transmission lines, are the lines that connect your transmission to the radiator in your car. The hot fluid cools off in the radiator and then heads back to the transmission. They're made up of a system of rubber hoses and metal or composite aluminum tubes that allow for transmission fluid to flow through them at high temperatures. If these are malfunctioning in some way, you'll be leaking transmission fluid and your system will overheat and fail pretty quickly. 


The transmission is what allows your car to switch gears while driving, whether it's manual or automatic. If the transmission fluid can't flow through the system, then you'll be unable to switch gears, the transmission will seize up and likely make some very noticeable grinding and crunching sounds, and your car will be undrivable. This fluid provides two key functions in your transmission;


  • Lubrication: The reason your gears grind when the fluid is contaminated, or levels are low is because you’re getting metal on metal grinding and that makes a terrible noise. Transmission fluid keeps it lubricated and running smoothly.
  • Cooling: Obviously your engine makes a lot of heat, but your transmission also operates at high temperatures if not properly cooled. The fluid cycles in and out to maintain a normal temperature range. With good quality fluid and functioning lines your transmission will ideally be running at around 175 degrees. If you drain that fluid and try to drive your transmission can heat up to a destructive 325 degrees, hot enough to cook your dinner and hot enough to destroy the transmission.


Transmission cooler line leak symptoms


There are a few ways to tell if your transmission cooler line is leaking just from inspecting it on your own before taking it to see a mechanic. 


  • The most obvious sign of a transmission cooling line leak is the presence of transmission fluid. Look for red fluid when you move your car or if you're under the hood, look around for that same red fluid on any hoses are gaskets. Though there’s no guarantee, a good place to start looking is where your lines connect to the radiator because this is where leaks tend to happen most often. Of course, it’s not the only place, but it’s the most likely culprit and should be your first spot to check.
  • Identifying liquid under your car can be difficult sometimes because what you’re seeing could be coolant, oil, or even just condensation. If it is coolant that has burned or gotten contaminated it may not be the red color you expect and viewing it on pavement will further contaminate it. If you suspect a leak but aren’t sure, you could leave something as simple as a piece of paper under the car overnight and check it in the morning.
  • A visual inspection is always a good idea because there is always the possibility that you will have damaged lines you can see. Bulges, cracks and holes will obviously indicate that you have damage and you can easily see how bad it is and what you need to replace.
  • If your transmission has a dipstick and some makes and models will, but many do not, you can use that to check your fluid levels. If the level is low, you may have a leak. If you're not sure about your car, check your owner’s manual to see.
  • Locate the radiator and check where the coolant lines are attached. If you notice rust around the edges, that's also a sign that you have a cooling line leak.
  • Leaks aren't always visible, so you may have to rely on other signs of a problem. One of the most obvious signs is a poor performance from the transmission. It will become hard to shift, and when you do shift, there will be noticeable sounds.
  • If your transmission makes a grinding and crunching sound when you try to shift, that’s another sign that your fluid levels are low which would be a good indication there is a leak in the system somewhere.
  • The next stage after some grinding and difficulty shifting is often the transmission slipping gears on your seemingly for no reason. You’ll find it dropping to a lower gear as you drive, for instance. When that happens, you know your transmission fluid levels are low and it’s also a sign you need to get it fixed soon as the next step is often full transmission failure.
  • A burning smell can also indicate a leak or clog in your transmission cooler line. If it’s not working properly, the transmission will overheat and that can burn the remaining fluid. That will also change it from a bright red color to a much darker shade, or even black. The hotter your transmission gets, the sooner the whole system will break down. Transmissions cannot work in high temperatures.


How do you fix a leaky transmission cooler line?


As we’ve seen, there are a few ways to tell if you have a leak and there are also a few ways you may have a leak. Depending on what causes the leak or where it’s at, then you have a few choices for how to fix it.


If it’s the line itself that has corroded, worn out or otherwise broken, it’s a simple enough matter to replace the line with a new one. Sites like Autozone have a wide variety of transmission cooling line assemblies you can buy. Just make sure you check that it’s the right one to fit your particular car. Prices average anywhere from $15 to $50. 


In a pinch you can also use a sealant on the line if it’s leaking at a connector. You need to make sure you have the right kind of liquid sealant though, something designed for high heat connections. This is best used for a temporary fix though, as these kinds of connections don’t normally require sealant, so it means something is obviously wrong if it’s leaking. Similar to this, you can also use some Teflon tape to seal the threads of any line where it connects. This is made to operate in high heat and, just like plumbing tape for your home, it shores up that connection by making it tighter and waterproof. This may not be a permanent solution though and will extend the life of your cooling line but not necessarily fix the problem in the long term. A roll of Teflon tape should cost around $3.


A third option is to get an adapter. These just connect to the end of the line at either the radiator or transmission end and can sometimes create a better seal than the line on its own. It’s worth trying, as some of these can be as cheap as about $6.


Is there a transmission cooling line repair kit?


You may have heard of or seen transmission cooling line repair kits and wondered if these were an option for repairing your own leaking coolant lines. They do exist, but these are not really geared for the casual consumer. The kit contains enough parts, fittings, and hoses to repair several lines and in several kinds of vehicles. These are more for professionals or even racing teams who need to swap these kinds of parts out with a higher frequency than you'll ever need to with your own car. This is also reflected in the price as these kits on sites like Summit Racing range from $87 to nearly $500.


Can I use rubber hoses to replace the transmission cooling line?


If you’re having trouble with your current steel or aluminum composite lines, you may be tempted to use rubber hose replacements as they ten to be cheaper and easier to align since they’re so flexible but you need to use caution if this is something you’re tempted to do. Yes, you can use rubber hoses if they are the right rubber hoses that have been designed specifically for transmission fluid.


Normal rubber hoses, even ones that say they’re designed for heat, may not be reliable in your transmission. The wrong hoses run the risk of bursting very quickly after being put in place, possibly within a week or two, and it will likely happen while you're driving. That means you'll be on the road as all your transmission fluid drains out and potentially causes your entire transmission to seize up.


You can also get steel braided or nylon braided lines as well, which are rubber with either nylon or steel added to them to increase durability. These will last longer than your typical, plain rubber line.


How long do transmission cooling lines last?


Transmission lines are supposed to last the life of your car. These aren’t like fuel filters or engine oil that wear out with use and need to be swapped on the regular. That being said, there’s no way to define for certain how long these things will last. Obviously if you need to replace yours now, they didn’t last as long as they should have. The new ones you get may last just as long but should last longer. Unfortunately, there are also unforeseen issues. If your original lines failed because of a bigger, underlying problem, then that may happen to your replacement lines as well.


How much does it cost to replace a transmission cooling line?


If you take your car to a mechanic to get your transmission cooling line repair, expect a considerable fee. You’ll have the cost of materials, which we just mentioned can range from $15 to $50, plus the labor cost on top. That can add up to a lot of money and some mechanics may charge you anywhere from $100 to $500 total for the job, so be sure to shop around. 


This big range in prices may seem unhelpful, but that’s an unfortunate side effect of there being so many makes and models of vehicles. Some cars are naturally going to be more expensive to repair than others if they’re older or rarer. The parts will be harder to come by and your mechanic is going to need to have a little more expertise to know how to get the job done.


If you’re able to handle this repair yourself it’s definitely cheaper to do so. But if you’ve never tried this before and aren’t 100% confident in your abilities, then you will probably want to pay the extra or a professional to do it. That ensures it’s done right, and that the problem won’t get worse. A damaged transmission will cost you even more.


Is it worth it to replace a transmission coolant line?


In a word, yes. In fact, you must replace a malfunctioning transmission cooling line. If you have a leak and do not fix it, you’re on a very short clock. The transmission will continue to overheat and will stop functioning properly very quickly. Your car is just not physically able to function in this condition. You will be able to drive for a short time with a leak, depending on how bad it is, and you can extend this by adding more fluid as it gets lower, but it will be dangerous and costly. The source of the leak can and likely will get worse as time passes. Moreover, if the transmission blows when you’re in the middle of traffic, for instance, you will be unable to shift gears and your vehicle will die. That’s dangerous for you and for other drivers. Not to mention the cost associated with this. Transmission repair is going to cost anywhere from $1,800 to $3,400. Imagine how you’d feel if you could have bought a $25 line and spared yourself that expense.


Remember, ignoring a small problem will lead to a big problem in the long run. 


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