Ford Fiesta Mk7 1.5 TDCi 75bhp — 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 Regeneration Failure
ModerateThe 1.5 TDCi diesel Fiesta is commonly used for short urban trips — exactly the wrong usage for a DPF-equipped car. Blocked DPF is the number one complaint.
EGR Valve Failure and Intake Carbonisation
ModerateEGR failure on the 1.5 TDCi Fiesta is a common companion to DPF issues. Carbon deposits block the valve and intake manifold, causing power loss and rough running.
Diesel Injector Failure and Rough Running
SevereCommon rail injectors on the 1.5 TDCi can fail, causing misfires, excessive smoke and hard starting. Injector failure can also result in diesel washing the cylinder walls, accelerating engine wear.
Disclaimer: Repair cost estimates are indicative and based on community data. Always get a quote from a qualified mechanic before proceeding with any repair.