Mini Hatch R56 Cooper S 1.6T 175bhp — 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
Timing Chain Tensioner Failure (N14 Engine)
CriticalThe BMW-designed N14 1.6T engine in the R56 Mini Cooper S has a plastic timing chain tensioner that fails prematurely. This is the most serious known fault on the R56 generation.
Carbon Build-Up on Intake Valves
ModerateThe N14's direct injection system means fuel is injected directly into the cylinder, bypassing the intake valves. Oil vapour from the PCV system coats the valves with carbon, causing power loss and misfires.
High Pressure Fuel Pump (HPFP) Failure
SevereThe High Pressure Fuel Pump on the N14 engine fails frequently. It is one of the most well-known and expensive failures on the R56 Cooper S.
Disclaimer: Repair cost estimates are indicative and based on community data. Always get a quote from a qualified mechanic before proceeding with any repair.