How to Identify Engine Coolant Leaks

Engine coolant leaks can lead to serious, expensive damage, so it’s important to diagnose and fix them as soon as possible.

Your vehicle’s coolant system comprises a network of tubes and hoses that connect to engine components. Coolant leaks can occur anywhere in this network.

Leaks usually fall into one of three categories: external leaks, radiator cap leaks and internal leaks.

External Engine Coolant Leaks

Coolant sometimes leaks on its journey from the engine – where it picks up heat – to the radiator, where it cools. External coolant leaks are the easiest to diagnose. If you spot any leaks coming from the hoses, radiator, coolant reservoir or tank, it’s likely to be an external leak, requiring a replacement car part. If you can see bubbles on the radiator, this is a sign of an external or an internal leak.

Radiator hoses are amongst the most common parts to crack as the rubber degrades over time. Even a tiny crack can cause a coolant leak. Connections between hoses and components are also common coolant leak culprits, as loose clamps can let coolant seep out. Damage to the radiator itself can also cause coolant leaks.

Radiator Cap Leaks

The radiator cap sustains the pressure that allows the coolant to flow around the network of tubes. Check the radiator cap to ensure it isn’t loose or damaged. Coolant leaks can also occur if the wrong radiator cap has been used. The recommended type for your model will be detailed in your vehicle handbook.

Internal Engine Coolant Leaks

If you have a coolant leak and can’t identify its source in the external system or radiator cap, you’re likely to be dealing with an internal leak.

Usually, internal leaks don’t lead to puddles of coolant beneath your car. Instead, you will normally find your coolant level dropping regularly, requiring frequent refills. This often means that the head gasket is leaking. The head gasket may degrade over time and cause leaks because it is constantly exposed to high-pressure hot gases.

It is difficult to check the condition of the head gasket under the bonnet. However, white smoke coming from the tailpipe is a strong sign that the head gasket is behind the leak. This is because coolant leaks into the combustion chamber, where it burns and evaporates.

Milky white oil on your dipstick is also a sign of an internal leak. This will require an instant oil change – ethylene/propylene glycol in the coolant will affect the oil’s lubricating properties. Contaminated oil will quickly destroy an engine.

Replacing Your Engine Coolant

You’ll need new engine coolant after fixing a coolant leak.

Search your number plate in our car lookup tool to find coolants suited to your vehicle.

Follow our step-by-step instructions on how to replace your coolant here.

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