A coolant leak was one of the most common problems I encountered with my clients’ cars during the winter. I discovered that many of you could fix it yourself if I posted it online. It is quite simple to solve, even if you have little expertise.
So why does coolant leak in cold weather? The primary reasons are the loosened expansion cap, leaks in the hose, and a radiator leak. Due to contraction and expansion, these components become brittle and crack, leading to leaks.
Nevertheless, knowing the names of the reasons is never enough to get rid of the problem. Don’t worry, as I will share the problems in-depth along with their solution. However, I would like to start with the symptoms first.

Symptoms Of Coolant Leak In Cold Weather
Let’s check out the symptoms first to confirm it’s a coolant leak due to cold weather.
- You will come across a strong, sweet, or syrupy odor.
- You will encounter an overheating engine, and the engine temperature gauge will be in the red zone.
- There will be puddles under the vehicle, which is the coolant leaking onto the ground.
- A coolant leak can also cause reduced engine performance, such as decreased power, sluggish acceleration, or difficulty starting the engine.
Why The Coolant Leak In Cold Weather Happens And How To Fix
The coolant thickens and loses its ability to flow freely in cooler temperatures, making engine coolant leakage more likely. In addition, as the engine coolant freezes, pressure in the coolant system when cold rises, increasing the risk of leaks from coolant hoses and gaskets.
Lastly, as already mentioned, the coolant freezes, expands, and shrinks, which causes the coolant hoses and gaskets to become brittle. As a result, it cracks easily.
Nevertheless, let’s get in-depth with the component that causes it and how you can fix it.
Expansion Tank Cap Leak
The expansion tank cap is essential for preserving the right amount of pressure in a car’s cooling system. However, during cold weather, the water inside the expansion tank cools down, causing the expansion tank cap to pressurize.
To be more precise, the cold water compresses the rubber gasket or O-ring that seals the top and causes it to leak. As a result, a loosened expansion tank cap is seen. Furthermore, the cold can make rubber materials more brittle and prone to cracking, which increases the risk of leakage.
The Fix
Here are the steps you need to follow to fix it;
- Locate the pressure relief valve on the radiator or near the cap and carefully open it to release any built-up pressure.
- Use a towel to carefully unscrew the expansion tank cap in a counterclockwise direction and take the cap out.
- Examine the cap for any visible signs of damage, such as cracks, worn-out seals, or corrosion.
- Replace the cap if you find any damage.
- If no damage is found, clean the cap thoroughly using water and mild detergent to take out any dirt in the coolant reservoir.
- Reinstall the cap onto the expansion tank by screwing it on in a clockwise direction and ensuring it’s tightly secured.
Leaks in the Coolant Hose
Hoses are an essential part of the cooling system as they transport coolant between the engine, radiator, and other components. In cold weather, the temperature drops significantly, causing materials to shrink, and this can lead to a leak in the hose.
When a hose develops a leak, coolant can escape from the system and cause a massacre.
The Fix
Here’s how you can fix a leaky hose;
- Locate the hose by opening the hood of your vehicle and find the radiator. It is usually on the side of the engine compartment or at the front of the vehicle.
- Inspect the hose carefully for any visible cracks and holes.
- Once found, locate the drain plug at the bottom of the radiator and open it for the coolant to drain out completely.
- Use a wrench to loosen any clamps or fittings, secure the hose in place, and take it out.
- Get a new coolant hose that has the same measurements and material type as the last one.
- Install the new hose by reversing the steps of the way you took the old hose out.
Here’s a video that should help replace the hose;
Radiator Leak
Radiators are typically made of metal, such as aluminum or copper. They are prone to expanding and contracting with temperature changes. As a result, small cracks or gaps form in the radiator. These gaps don’t affect that much during summer, but during freezing temperatures, the leaks are more pronounced.
Nevertheless, there is also a chance that your radiator is quite old. Thus, the material is not too strong due to corrosion, wear and tear, or damage from external factors. So, even with small contraction and expansion, the weakened components of the radiator start to form gaps, resulting in coolant leaks.
The Fix
You need to stop small leaks or replace the radiator itself if the leak is too big. Here’s how you can do it;
- Open the hood of your vehicle and find the radiator.
- Visually inspect the radiator for any leaks. The leaky spots should have stains on them.
- If there are minor leaks, simply use a radiator stop leak additive to stop the leak by following the guidelines provided by the manufacturer.
- In case of big leaks, I recommend you take it out to a professional. They require extensive repair that requires specialized tools and experience.
Conclusion
Most cases of a coolant leak in cold weather can be corrected by you. However, for radiator leaks, professional assistance is required.
Nevertheless, once you understand the science behind low temperatures, the mystery behind the reasons behind a coolant leak gets easier. As the hose, expansion cap, and radiator expand and contract, the components feel pressurized. As a result, sometimes the components give up and leak, which then lets the coolant flow out.