Vauxhall Astra Astra H 1.7 CDTi 100bhp — 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
EGR Valve Failure
ModerateThe Isuzu-sourced Z17DTH and Z17DTJ engines in the Astra H have a well-documented EGR valve failure. Carbon deposits cause the valve to stick, resulting in power loss and increased emissions.
DPF Blockage
ModerateDPF-equipped Astra H 1.7 CDTi models (post-2007) suffer from the same DPF blockage issues as most diesel Vauxhalls of this era. Urban use is the root cause.
Dual Mass Flywheel Failure
ModerateDMF wear on the Astra H 1.7 CDTi is a high-mileage inevitability. The flywheel's internal dampers lose effectiveness, causing vibration and judder that makes the car unpleasant to drive.
Disclaimer: Repair cost estimates are indicative and based on community data. Always get a quote from a qualified mechanic before proceeding with any repair.