A Mercedes-Benz owner came in with a persistent coolant leak. After replacing the expansion tank and hoses on the first visit, the leak recurred. On the second visit the thermostat, coolant lines and water pump were all replaced. The owner confirmed the car has been fine since.
Job completed: September 2026
| Car | Mercedes-Benz |
|---|---|
| Symptom | Coolant leak, coolant level dropping |
| Fault found | Multiple coolant hoses, expansion tank, thermostat and water pump all contributing to coolant loss |
| Repair done | First visit: expansion tank and multiple coolant hoses replaced. Second visit: thermostat, thermostat coolant line, coolant hose to cooler, water pump, water pump to cylinder head hose replaced; coolant refilled |
| Parts | Quality coolant system components, Mercedes-grade parts |
| Time taken | Two visits; timeline confirmed at each booking |
| Cost | Itemised quote approved before each visit |
| Warranty | Owner confirmed no further leaks after both visits |
The owner contacted us about a coolant leak. The coolant level had been dropping and there was visible evidence of a leak.
We inspected the full coolant circuit and identified the most obvious sources of the leak. A quote was prepared for the first round of repairs covering the expansion tank and the worst-affected hoses.
Modern Mercedes-Benz engines use a pressurised cooling circuit with multiple hoses, an expansion tank, a thermostat and a water pump working together. The thermostat controls coolant flow based on engine temperature. The water pump circulates coolant through the engine and radiator.
As the car ages, the plastic expansion tank and the rubber hoses can degrade. Hose fittings can weep coolant before the hose itself splits. The thermostat housing seal and the water pump seals are other points where coolant can leak.
A full pressure test of the cooling circuit after any repair is the right way to confirm there are no remaining leak points.
On the first visit, inspection of the coolant circuit revealed the expansion tank and several hoses were deteriorated and leaking. These were replaced and the system was refilled before handover.
The owner returned after the coolant level dropped again. On the second inspection, the thermostat and its housing were found to be the source of the remaining leak, with the water pump also showing signs of failure. The coolant lines to and from the thermostat and the hose from the water pump to the cylinder head were also replaced at the same time.
All components were explained to the owner and an itemised quote was produced before any second-visit work started.
A Mercedes-Benz coolant leak gets two checks at our workshop. We pressure test the cooling system to show where it is weeping, and we diagnose it with XENTRY, Mercedes-Benz's own diagnostic system, which reads the fault memory and the live coolant temperature.
A coolant system runs at continuous elevated temperature and pressure during engine operation. Rubber hoses, plastic fittings and seals all age at different rates. When one hose starts to show age, others in the same circuit are usually not far behind.
The thermostat and water pump are internal components that are harder to inspect without dismantling. When a hose repair does not fully resolve a coolant loss, the next step is to check the thermostat housing and the water pump weep hole. On this Mercedes, both were contributing to the ongoing leak and were addressed in the second visit.
Fixing everything at once in the second visit, rather than replacing parts one by one, is the more thorough approach once the internal sources are confirmed.
First visit:
Second visit:
The car was confirmed good to go before handover.
From our team's record of this job. Number plates are pixelated.
The cost of a Mercedes-Benz coolant repair depends on which components are the source of the leak. Common items are hoses, the expansion tank, the thermostat and the water pump. On this Mercedes, the thermostat and water pump were replaced together with the coolant hoses so the leak was addressed at every identified source in one go.
We provide an itemised quote at each visit before any work starts. Every item is approved by the owner before we begin. The quote covers parts and labour separately so you know exactly what each item costs.
Coolant should be replaced on schedule. Old coolant loses its anti-corrosion inhibitors, which accelerates degradation of seals, hoses and aluminium components in the cooling circuit.
At each service, ask for a visual inspection of the coolant hoses and expansion tank. Swelling, cracks or discolouration around a hose fitting are early signs worth addressing before a hose fails completely.
If you notice your coolant level dropping between services, or a sweet smell from the engine bay, get it checked promptly. A small coolant leak can cause overheating if left, which is a significantly more expensive repair than fixing the original source.
This Mercedes-Benz (coolant leak repair, thermostat replacement, water pump replacement) was handled at 1 Car Service, an independent workshop in Sin Ming AutoCity, Singapore. For Mercedes-Benz, we use dealer-level XENTRY diagnostics. We hold a 4.9★ rating from 1,831+ Google reviews.
WhatsApp us your symptoms and model. We pressure test the cooling system, read the fault memory on XENTRY and quote every component before starting.
It depends on which parts are the source of the leak. Hoses and an expansion tank are less expensive; a thermostat and water pump add to the cost. We quote every item separately after inspection. WhatsApp us your model and symptoms and we will advise what needs checking.
Yes. We pressure test the cooling system and diagnose it with XENTRY, Mercedes-Benz's own diagnostic system. The pressure test shows where the coolant is escaping. XENTRY reads any stored fault codes and the live coolant temperature.
When hoses are replaced and the leak returns, the next components to check are the thermostat housing seal and the water pump. These are internal components that may not show a visible external leak until they fail further. A pressure test of the cooling system after any repair helps confirm whether all sources have been addressed.
Not advisable. A small leak can become a large one without warning, and driving with low coolant risks overheating the engine, which is a significantly more expensive repair. If you notice the coolant level dropping, get it checked as soon as possible. WhatsApp us and we can advise based on your symptoms.
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