Updated: Feb 1
✔ This article has been fact checked.
Transmission cooler lines are a crucial component in the functioning of your car's transmission system. These lines are responsible for transporting fluid from the transmission to the radiator, where it is cooled before being sent back to repeat the cycle.
A leak in the transmission cooler line at the radiator can cause serious issues, such as transmission failure, overheating, slipping and inability to change gears, and more. Thankfully, there are some obvious signs to look out for.
In this article, we will look the causes and symptoms of a transmission fluid leak at the radiator and the ways you can fix it. We'll also discuss the severity of this issue and other information you should know.
Table of Contents:
What Are Transmission Cooler Lines?
Transmission cooler lines are the hoses that transport transmission fluid from the transmission to the radiator. The transmission fluid is cooled by the radiator, and then sent back to the transmission to repeat the cycle.
These lines are typically made of metal (such as stainless steel), rubber, or a braided material and are connected to the transmission and radiator by fittings.
The image below shows three examples of what these fluid lines look like.
How Serious Is a Transmission Cooler Line Leak?
A transmission cooler line leak can be serious if left untreated. If the transmission fluid level drops too low, the gearbox can overheat and be damaged.
In addition, the transmission can lose its ability to shift gears properly, which can cause further damage to the transmission system. In some cases, a transmission cooler line leak can also cause the transmission to fail completely.
Symptoms of Leaking Transmission Cooler Lines
There are a few signs that can indicate a transmission cooler line leak.
Transmission fluid leaking: One of the most obvious signs is a puddle of transmission fluid under the car near the radiator. This fluid is typically red or pink in color.
Burning smell: Another sign is a burning smell coming from the transmission or radiator.
Transmission slipping or not shifting properly: You may notice that the transmission is slipping or not shifting gears properly.
Discoloured coolant: You may notice that the coolant is discoloured from the mixing of transmission fluid and coolant in the radiator, this could create a "strawberry milkshake" colour.
Overheating: If the radiator is leaking coolant or mixing with transmission fluid, you may notice the engine has tendency to overheat.
Below is an image of rusty transmission coolant lines. You may find a fluid leak around these lines and connections.
Can Transmission Fluid Leak Into the Radiator?
Yes, transmission fluid can leak into the radiator if the transmission cooler lines are leaking. If this happens, you may notice that the radiator fluid has become discolored or has a burnt smell.
Additionally, the transmission fluid can cause damage to the radiator, which can lead to further leaks or even a complete failure of the radiator.
Can a Leaking Transmission Cooler Line Cause Overheating?
Yes, a leaking transmission cooler line can cause overheating. If the transmission fluid level drops too low, the gearbox can overheat and be damaged.
If the transmission fluid leaks into the radiator, it can cause the coolant fluid to overheat and potentially cause engine failure.
How to Know if Coolant Lines Are Leaking?
There are a few signs that can indicate a coolant line leak.
One of the most obvious signs is a puddle of coolant or transmission coolant fluid under the car, usually underneath the engine bay or radiator.
A burning smell coming from the engine area.
You may notice that the engine is running hot or that the temperature gauge is reading higher than normal.
You need to inspect the transmission lines and the radiator for leaking or issues to determine if the issue is caused by transmission fluid lines or coolant hoses.
How to Fix Transmission Cooler Line Leak at Radiator
To fix a transmission cooler line leak at the radiator, the first step is to locate the leak. This can be done by visually inspecting the lines or by using a pressure tester to check for leaks.
Once the leak is located, the damaged line or fitting can be replaced. In some cases, it may be necessary to replace the entire transmission cooler line or even the heater matrix or radiator.
Transmission Cooler Line Leak After Replacing Radiator
It is common for a transmission cooler line leak to occur after replacing the radiator. This can be caused by a faulty radiator installation or by damage to the transmission cooler lines during the radiator replacement.
To fix this problem, the transmission cooler lines and radiator should be inspected and any damaged or leaking lines should be replaced or repaired.
What Happens if Transmission Fluid Leaks Into the Radiator?
If gearbox fluid leaks into the radiator, it can cause damage to the radiator and lead to further leaks or even a complete failure of the radiator or the engine.
Additionally, the transmission fluid can cause the coolant to become discolored or have a burnt smell.
The transmission fluid can also cause damage to the engine and transmission if the fluid level drops too low. In severe cases, the transmission can fail completely or the engine can overheat and fail.
Why Do Transmission Lines Go to the Radiator?
Transmission lines go to the radiator to cool the transmission fluid. As the transmission fluid is circulated through the transmission, it can become heated due to friction and other factors.
The radiator helps to dissipate this heat, keeping the transmission fluid at the proper temperature to ensure proper functioning of the transmission.
How Do Transmission Cooler Lines Connect to the Radiator?
Transmission cooler lines connect to the radiator by fittings. These fittings are typically located on the transmission and the radiator (as shown in the image below).
The fittings are designed to be tight and secure to prevent leaks but they can sometimes fail.
How Do You Stop a Transmission Line From Leaking?
To stop a gearbox line from leaking, the damaged line or fitting must be replaced. In some cases, it may be necessary to replace the entire hose.
It is also important to regularly check and maintain the transmission cooler lines to prevent leaks from occurring in the first place.
How Much Does It Cost to Replace or Repair Transmission Cooling Lines?
The cost to replace or repair transmission cooling lines can vary depending on the specific vehicle and the extent of the damage.
On average, most transmission cooler line repairs cost between $100 (approx. £75 or €85) and $500 (approx. £365 or €415).
However, in some cases, the repair can be more expensive, especially if the transmission or radiator is also damaged.
A transmission cooler line leak at the radiator can be a serious problem that can cause damage to the transmission and engine. It is important to be aware of the signs of a leak, such as a puddle of transmission fluid or a burning smell, and to have any leaks repaired as soon as possible.
Regular maintenance and inspection of the vehicle can help prevent leaks from occurring in the first place. If you suspect a transmission cooler line leak, it is important to have your vehicle inspected by a qualified mechanic.
Tsukasa Azuma. "Everything You Need To Know About Transmission Cooling Lines Leaking". https://carfromjapan.com/article/car-maintenance/transmission-cooling-lines-leaking/