Ford Focus Mk3 1.6 TDCi 115bhp — 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
MinorDIY Difficulty
Moderate
Est. Cost
£100–£250
OBD Codes
P0128Cooling
Typical layout and location for the Cooling assembly.
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
DPF Blockage and Forced Regeneration Failure
ModerateDPF blockage is the most reported issue on the Focus Mk3 1.6 TDCi. City driving prevents regeneration, and the DPF warning light becomes a familiar sight for urban Focus diesel owners.
EGR Valve and Cooler Failure
SevereThe EGR valve and cooler on the Mk3 Focus 1.6 TDCi are known to fail together. EGR cooler failure can cause coolant to enter the intake — a more serious failure than a simple blocked valve.
Turbocharger Failure
SevereThe turbocharger on the Focus Mk3 1.6 TDCi is vulnerable to bearing wear from oil sludge and extended service intervals. Failure typically presents as a sudden loss of power with a loud noise.
Disclaimer: Repair cost estimates are indicative and based on community data. Always get a quote from a qualified mechanic before proceeding with any repair.