ModerateAffected: 2012-201850,000–100,000 miles

Ford Fiesta Mk7 1.0 EcoBoost 100bhp — Thermostat Failure and Overheating Risk

The plastic thermostat housing on the 1.0 EcoBoost is prone to cracking. A stuck-open thermostat causes the engine to run cold and burn more fuel; a stuck-closed thermostat causes rapid overheating.

Severity

Moderate

DIY Difficulty

Moderate

Est. Cost

£80–£180

OBD Codes

P0128P0217

Component Diagram

Cooling

Typical layout and location for the Cooling assembly.

Reference Illustration

Symptoms

Engine takes very long to reach normal temperature
Heater blows cold even after 10+ minutes driving
Fuel consumption noticeably worse
Temperature gauge swings unpredictably
Coolant warning light

Root Cause

The thermostat is integrated into a plastic housing bolted to the engine block. The housing develops hairline cracks from thermal cycling, causing coolant to leak. The thermostat element itself fails open or closed with age.

How To Fix

Replace thermostat and housing together as a unit — they are sold as an assembly
Drain coolant before removal — use Ford-spec orange coolant on refill
Bleed cooling system carefully — the 1.0 EcoBoost is prone to air locks
Parts cost: £30-60. Labour: 1-2 hours. Total: £80-180 at indie garage

Estimated Repair Costs

Repair Option	Est. Cost (GBP)
DIY (parts only)	£32–£72
Independent Garage	£80–£180
Main Dealership	£128–£288

Other Faults on This Variant

Timing Chain Stretch and Tensioner Failure

Critical

2012-201540,000–100,000 miles£600–£1200

Pre-2016 Ford 1.0 EcoBoost engines suffer from premature timing chain stretch. The plastic tensioner can fail, causing catastrophic engine damage with little warning.

Coolant Loss from Cylinder Head

Severe

2012-201860,000–120,000 miles£500–£900

The 1.0 EcoBoost has an integrated exhaust manifold cast into the cylinder head. This design causes head gasket stress and coolant loss, sometimes causing overheating.

Clutch Wear and Judder on Engagement

Moderate

2012-201850,000–90,000 miles£400–£700

The lightweight flywheel and small clutch on the 1.0 EcoBoost are undersized for the turbo torque. Clutch wear and judder on biting point is common from 50,000 miles, especially in urban use.

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