MinorAffected: 2012-201960,000–120,000 miles

Renault Clio Mk4 0.9 TCe 90bhp — Engine Thermostat Sticking Open

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Severity

Minor

DIY Difficulty

Moderate

Est. Cost

£100–£250

OBD Codes

P0128

Component Diagram

Cooling

Typical layout and location for the Cooling assembly.

Reference Illustration

Symptoms

Temperature gauge drops when driving on the motorway
Heater blows lukewarm air in winter
MPG drops significantly
Engine takes a very long time to warm up

Root Cause

The wax element inside the thermostat degrades, or the return spring weakens, preventing the valve from closing off coolant flow to the radiator.

How To Fix

Scan for P0128 (Coolant Thermostat - Coolant Temp Below Regulating Temp).
Replace the thermostat housing unit and gasket.
Bleed the cooling system of air.
Cost: £100-250

Estimated Repair Costs

Repair Option	Est. Cost (GBP)
DIY (parts only)	£40–£100
Independent Garage	£100–£250
Main Dealership	£160–£400

Other Faults on This Variant

Thermostat Housing Leak

Severe

2012-201940,000–80,000 miles£150–£200

The plastic thermostat housing on the 0.9 TCe warps and cracks, leading to a rapid loss of engine coolant and severe overheating risk.

Timing Chain Stretch and Rattle

Severe

2012-201950,000–90,000 miles£600–£800

The 0.9 TCe 3-cylinder engine suffers from premature timing chain stretch, causing an aggressive rattle and potentially fatal engine timing slip.

VVT Solenoid Oil Leak

Minor

2012-201950,000–100,000 miles£10–£80

The Variable Valve Timing (VVT) solenoid located on the top of the cylinder head leaks oil, which runs down the front of the engine.

Disclaimer: Repair cost estimates are indicative and based on community data. Always get a quote from a qualified mechanic before proceeding with any repair.