How much does a Mercedes coolant leak repair cost?

A coolant leak in a Mercedes should never be ignored. Even a small leak can lead to overheating and engine damage, and, if left untreated, to costly repairs.

The average Mercedes coolant leak repair cost ranges from £90 to £900, depending on which engine part needs to be replaced.

In this article, we break down the differences between Mercedes repair costs, the causes behind them, and how quickly repairs can be completed, helping you act early and keep costs under control.

How much is a Mercedes coolant leak repair cost?

The cost of repairing a coolant leak on a Mercedes in the UK typically ranges from £90 to £900, depending on the source of the leak and the Mercedes model.

Minor issues at the lower end of the cost spectrum, such as a loose hose or a cracked expansion tank, are relatively affordable.

However, leaks involving the radiator, thermostat housing, or water pump can significantly increase repair costs due to parts and labour.

On average, early diagnosis keeps costs at the lower end of the scale, while delayed repairs often result in higher bills. You can also use car repair finance to split the fee into interest-free repayments.

Are coolant leaks expensive to repair?

A £900 price tag is shocking, but the good news is that coolant leaks are not always expensive to fix, especially if caught early. Small leaks caused by worn hoses or faulty seals are often quick and inexpensive repairs.

However, coolant leaks become costly when:

The water pump or radiator is involved
Coolant loss causes engine overheating
Plastic components crack due to age or heat

Mercedes vehicles use high-quality but complex cooling systems, so labour costs can increase if multiple components must be removed to access the leak.

Common Mercedes coolant leak repair costs by component

Prices vary by model, what needs to be repaired, the extent of damage, and whether genuine Mercedes parts are used.

Here are typical UK repair costs for common Mercedes coolant leak sources in 2026:

Component	Typical Cost (£)	What’s Involved
Coolant hose	£90 – £180	Hose replacement and system pressure test
Expansion tank	£120 – £250	Tank replacement and coolant refill
Radiator	£300 – £600	Radiator replacement and bleeding system
Thermostat housing	£200 – £400	Housing replacement and temperature testing
Water pump	£450 – £900	Pump replacement, labour-intensive

How long does a coolant leak repair take?

Repair time depends on the source of the leak and vehicle layout. Your garage will confirm timings after a pressure test and inspection.

Typical repair times include:

Hose or expansion tank replacement: 1 to 2 hours
Thermostat repair: 2 to 4 hours
Radiator replacement: 3 to 5 hours
Water pump replacement: 4 to 6 hours

Why is my Mercedes leaking coolant?

Mercedes coolant leaks are often caused by ageing components exposed to constant heat and pressure. Over time, plastic parts can become brittle, and rubber hoses may weaken or crack.

Leaks may also occur due to:

Failed seals or gaskets
Corrosion within the cooling system
Poor previous repair work

What is the most common cause of a coolant leak?

The most common cause of coolant leaks in Mercedes vehicles is cracked plastic components, particularly expansion tanks and thermostat housings.

Mercedes engines run hot by design, which accelerates wear on plastic cooling parts. Once cracks form, coolant loss can escalate quickly. Even a slow leak should be inspected promptly.

Why am I losing coolant but not overheating?

It’s possible to lose coolant without immediate overheating, especially if the leak is slow.

Modern Mercedes engines have sensors and cooling reserves that can temporarily compensate for minor losses.

However, coolant levels can drop suddenly, leading to overheating without warning. Regularly topping up coolant is not a solution. The leak should be repaired as soon as possible.

Which Mercedes models are most prone to coolant leaks?

Coolant leaks are commonly reported in:

C-Class (W204, W205)
E-Class (W212, W213)
A-Class and CLA models
GLC and GLA SUVs

Models with high-mileage petrol engines or older diesel variants are particularly susceptible due to ageing plastic components.

Can you drive a Mercedes with a coolant leak?

Driving with a coolant leak is not recommended.

While short journeys may be possible, continued driving increases the risk of overheating and severe engine damage.

If you must drive, keep journeys short, monitor temperature warnings, and stop immediately if the engine overheats.

Is a coolant leak an MOT failure on a Mercedes?

Yes, a coolant leak can cause an MOT failure if fluid is visibly leaking or dripping.

Likewise, excessive leaks, overheating warnings, or engine-related warning lights may also result in failure.

Keep an eye on these symptoms, as even minor leaks should be repaired before an MOT test.

What happens if you ignore a coolant leak?

Don’t put off seeing your garage. Ignoring a coolant leak can lead to other issues, like:

Engine overheating
Blown head gasket
Warped cylinder head
Complete engine failure

What starts as a £100 hose repair can quickly become a multi-thousand-pound engine repair if left untreated.

Final thoughts

Mercedes coolant leak repairs vary in cost, but early diagnosis is the key to keeping bills manageable. In general, small leaks are inexpensive to fix, while delayed repairs can lead to serious engine damage.

If you notice coolant loss, warning lights, or puddles under your car, book a professional inspection as soon as possible to protect your Mercedes and avoid unnecessary costs!

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