Volkswagen Golf Mk5 2.0 TDI 140bhp — 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
High Pressure Fuel Pump Cam Follower Wear
CriticalThe PD (pumpe-düse) 2.0 TDI uses a mechanical cam follower to drive the high-pressure fuel pump. This follower wears rapidly and if not replaced destroys the camshaft — a £2,500 repair for a £15 part.
Dual Mass Flywheel Failure
SevereDMF failure on the Golf Mk5 2.0 TDI is a rite of passage for high-mileage cars. The flywheel absorbs diesel engine vibrations but wears out — often needing clutch replacement at the same time.
Gearbox Dogbone Mount Bush Failure
MinorThe lower engine pendulum mount (often called the dogbone mount) bushes perish, causing excessive engine movement, clunking, and sloppy gear changes.
Disclaimer: Repair cost estimates are indicative and based on community data. Always get a quote from a qualified mechanic before proceeding with any repair.