Mini Hatch R56 Cooper S 1.6T 175bhp — Thermostat Housing Leak and Failure
The plastic thermostat housing on the R56 warps and cracks, causing coolant leaks. The integrated temperature sensor also fails, causing erratic fan behaviour.
Severity
ModerateDIY Difficulty
Moderate
Est. Cost
£200–£350
OBD Codes
P0128Cooling
Typical layout and location for the Cooling assembly.
Symptoms
- Coolant pooling on top of the gearbox casing
- Sweet smell of coolant after driving
- Radiator fan stays on maximum speed long after parking
- Overheating warning
- P0128 fault code
Root Cause
Thermal cycling weakens the plastic housing. The glued seams eventually separate. The integrated sensor fails internally, causing the ECU to panic and run the fan constantly.
How To Fix
- Check for crusty coolant residue on gearbox below the housing
- Replace thermostat housing as a complete unit (£60-120 part)
- Requires draining and vacuum-bleeding the cooling system (system is notoriously hard to bleed)
- Fitted cost: £200-350
Estimated Repair Costs
| Repair Option | Est. Cost (GBP) |
|---|---|
| DIY (parts only) | £80–£140 |
| Independent Garage | £200–£350 |
| Main Dealership | £320–£560 |
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.