When a coolant thermostat fails, the engine's ability to reach and hold its correct operating temperature collapses. Fitted between the engine block and the radiator, the thermostat is a wax-element valve that opens at a precise calibrated temperature — typically between 82°C and 92°C for most European petrol and diesel engines — allowing coolant to flow through the radiator once the engine is warm. A thermostat that sticks open causes the engine to run permanently cold, increasing fuel consumption, accelerating bore wear and preventing the cabin heater from reaching useful output. Far more dangerous is a thermostat that sticks closed: coolant cannot reach the radiator, temperature climbs rapidly, and overheating damage to the head gasket or cylinder head can follow within minutes. Neither failure announces itself loudly — a temperature gauge that takes an unusually long time to climb in winter, or one that climbs higher than normal in traffic, are the typical warning signals. The OE reference matters because opening temperature and housing geometry vary between engine variants; fitting a unit calibrated for a different thermostat range causes subtle but persistent running issues. Motorad and CALORSTAT by Vernet are among the dominant original-equipment thermostat suppliers for European platforms.
The thermostat's opening temperature and housing dimensions are specific to each engine family — sometimes even differing between the same engine displacement in different model years. Use your vehicle's make, model, year and engine code to filter the OE references on this page, and cross-check against the number printed on your existing thermostat housing if it's still legible. Getting the correct opening temperature is especially important: a thermostat calibrated for a warmer opening point than your engine expects will keep it running too cool, affecting emissions and fuel economy.
OEM thermostats are produced to the vehicle manufacturer's temperature specification, typically by suppliers such as Motorad or CALORSTAT by Vernet, and carry the exact OE reference. Quality aftermarket units from these same suppliers are functionally identical — the wax element formulation and housing geometry are matched to the OE drawing. Cheaper generic thermostats can drift from their stated opening temperature over time or fail to seal fully when cold, causing erratic temperature gauge behaviour and reduced heater output long before complete failure.
On many modern engines the thermostat and housing are sold as an integrated assembly because the housing incorporates cooling passages, sensors and quick-connect hose fittings that cannot be reliably resealed after the original gasket has been disturbed. For older engines where the thermostat is a standalone disc-type unit sitting in a reusable housing, replacing only the thermostat and its gasket is perfectly acceptable provided the housing is clean and undistorted. Always replace the housing gasket or O-ring alongside the thermostat regardless of configuration.
A thermostat stuck open causes the temperature gauge to remain in the low portion of its range even after a long drive, the cabin heater to blow only lukewarm air, and noticeably higher fuel consumption. A thermostat stuck closed is more urgent: the temperature gauge climbs past the normal band and into the red zone, often accompanied by steam from the engine bay and a coolant smell. Either symptom warrants immediate investigation — running too cold causes long-term damage from fuel dilution and bore wash, while overheating can destroy a head gasket in a single incident.
Showing 100 of 11,043 Coolant thermostat OE numbers. Enter the OE on the main OE search to jump to any reference.
