Why Is My Car Losing Antifreeze?
FixMyCar explains why your car might be losing antifreeze and what you can do about it.
Book a fluid leak repairEllie Dyer-Brown
Tuesday July 29 2025
4 min read
Antifreeze is a concentrated version of coolant, although the names are often used interchangeably. It plays a vital role in keeping the engine at the correct operating temperature.
Most modern cars have a sealed cooling system, so if you’re losing antifreeze/coolant, there’s probably a leak. Find out where the fluid leak might be coming from, what you can do about it, and how much a repair will cost in this guide.
Why is my car leaking coolant?
Most coolant leaks happen due to wear and tear or corrosion. All parts must be in good condition for the system to remain sealed, so if you don’t carry out regular vehicle maintenance, you’re putting yourself at risk of a leak.
Signs of a coolant leak
The most obvious sign of a leak is low coolant, which can be checked by inspecting the reservoir in the engine bay. Additionally, you might notice:
Puddle of coolant under your car
Sweet smell from under the bonnet
What can cause a coolant leak?
1. Corroded or damaged radiator
The radiator has a network of tubes and fins that exchange heat between the hot coolant and the outside air. Over time, the radiator can rust, weakening its metal and potentially leading to leaks.
2. Leaking radiator cap
The radiator cap creates a tight seal to ensure the radiator stays at the correct pressure. If the cap deteriorates, the seal could be broken, allowing coolant to leak out.
3. Worn-out gasket
The gasket between the coolant tank and radiator is another part that can wear out and cause leaks.
4. Blown head gasket
The head gasket is located between the engine block and the cylinder head. It prevents coolant, oil and combustion gases from mixing. In addition to coolant loss, the most common symptoms when it wears out or ‘blows’ are:
Milky oil
You should never drive with a blown head gasket.
Find out how much it costs to replace a head gasket in this guide.
5. Failed water pump
The water pump circulates coolant around the cooling system. It can cause a leak due to the failure of internal seals and gaskets. It is also connected to the lower radiator hose, which can become loose or corroded, allowing coolant to escape.
6. Cracked hoses
Over time, the radiator hoses can become cracked, allowing coolant to escape as it is circulated through the system.
The dangers of driving with a coolant leak
Driving with low coolant can damage the engine. Here’s why.
Overheating engine
If the coolant drops below the required level, it won’t be able to cool the engine enough. The temperature will rise, and if you continue to drive, it could lead to engine failure.
Learn about the other problems that can cause an engine to overheat.
Head gasket failure
The leading cause of head gasket failure is an overheating engine. Low coolant allows the engine temperature to rise beyond a safe level, which can warp the cylinder head and block, leading to a blown head gasket.
How much does it cost to fix a coolant leak?
The cost of the repair depends on the location and cause of the leak, plus your vehicle make and model. It usually isn't possible for a mechanic to estimate the cost of fixing a leak without inspecting your car first to determine what repair is needed. That's why you'll often receive a quote for an initial diagnostic test.
| Repair type | Average cost |
|---|---|
| Coolant hose replacement | £111.35 |
| Head gasket replacement | £780.22 |
| Radiator leak | £212.49 |
| Water pump replacement | £310.27 |
Book a coolant leak repair
Driving with a coolant leak is usually a bad idea because it puts the engine at risk of overheating.
Unless you are certain that the leak is very small and won’t cause the coolant level to drop significantly during the drive to a garage, it’s best to book a mobile mechanic who will come to your location.
Discover the advantages of using a mobile mechanic.
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Ellie is FixMyCar's Content Manager. She has over three years of experience writing about cars and regularly collaborates with automotive experts to provide trustworthy advice for drivers that is easy understand. Her work has been featured in Yahoo! Finance, iNews, The Daily Express and The Sun. She has a BA in English literature and an MA in creative writing from Durham University. Outside of work, Ellie follows F1 and eagerly awaits Ferrari's next era of dominance in the sport. She drives a Suzuki Swift.