MinorAffected: 2004-201160,000–120,000 miles

Ford Focus Mk2 1.6 TDCi 110bhp — 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

EGR Valve Failure

Moderate

2005-201160,000–120,000 miles£80–£300

The EGR valve is a common failure on the 1.6 TDCi engine, causing power loss, rough idle, and excessive smoke.

Dual Mass Flywheel (DMF) Failure

Severe

2004-201180,000–150,000 miles£600–£1200

DMF failure is one of the most expensive known faults on the 1.6 TDCi. Typically requires replacement of flywheel and clutch together.

Turbocharger Failure

Severe

2004-2011100,000–180,000 miles£400–£900

Turbo failure on the 1.6 TDCi is common at higher mileages, often caused by oil starvation or sludge blockage.

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