Part explained
Thermostat replacement: price and symptoms
The thermostat regulates coolant flow so the engine warms quickly and stays warm. A fault: stuck open (engine stays cold) or stuck closed (overheats). This page covers symptoms, price, and how to find a fitting unit.
By the onderdelen.autos editorial team · Updated
What does the thermostat do?
A wax-filled valve opening at ~82 – 92 °C, sending coolant to the radiator. Below that it stays closed for faster warm-up. Wear sits in the wax and rubber; sticking open or closed is most common.
Symptoms
- Engine fails to reach operating temperature (stuck open).
- Engine overheats (stuck closed).
- Fault code P0128 / P0125.
- Cabin heater works poorly or only after a long drive.
- Higher fuel consumption in cold months.
When to replace
Indicative 100,000 – 200,000 km. Reactive — except when the water pump is being replaced for a timing belt service, in which case do the thermostat too.
Typical interval: 100,000–200,000 km
What does it cost?
New: € 25 – € 120 (electronic version costs more). Workshop labour: 1 – 2 hours.
| Condition | From | To |
|---|---|---|
| New | € 25 | € 120 |
| Used / refurbished | € 8 | € 30 |
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DIY?
Difficulty: Medium
Half-day work. Bleeding the cooling system per manual is essential — an air bubble mimics a stuck thermostat.
- Socket set
- Coolant catch pan
- Fresh coolant + bleed procedure
Frequently asked questions
How do I confirm the thermostat is bad?
Warm the engine + feel the radiator hose. Briefly warm after operating temp (valve opens) = OK. Not warm at 90 °C = bad.
What is an electronic thermostat?
An ECU-controlled version that can adjust opening temperature per load. More expensive; verify compatibility.
Can I buy a used thermostat?
Prefer not — the part is cheap new.
Workshop cost?
€ 100 – € 300 including the part.
Which coolant?
Per the manual (G11/G12/G12+/G13). Do not mix types.
Related parts
Thermostats from Dutch inventory
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