HELLA8MT 354 778-481Art. 8MT 354 778-481£20.99
Also known as: Coolant thermostat, Coolant Thermostat, Car Thermostat, Thermostat
OEM & aftermarket engine thermostat from top brands — compare prices, check fitment, order with free delivery
Shop 11546 engine thermostat from 24 trusted brands including MOTORAD, CALORSTAT by Vernet, EPS. Compare prices, check vehicle compatibility, and get free delivery on orders over £99.
The engine thermostat is a temperature-sensitive valve that regulates coolant flow between the engine and radiator, allowing the engine to reach its optimal operating temperature quickly and maintaining it throughout the drive. A stuck-open or stuck-closed thermostat causes overheating or chronic under-temperature running, both of which increase wear and emissions.
At cold start the thermostat remains closed, blocking coolant flow to the radiator and allowing the engine block to warm up rapidly. Once coolant temperature reaches the thermostat's rated opening temperature — typically 82–95 °C depending on the engine — a wax element expands and opens the valve, allowing hot coolant to flow to the radiator for cooling.
Some modern vehicles use electronically controlled thermostats that can vary the opening temperature according to engine load and driving conditions, improving both fuel economy and emissions. These map-controlled units require the correct replacement part for that specific engine management system.
A thermostat stuck open causes the engine to run permanently cold — the temperature gauge never reaches the middle of its range, the heater blows lukewarm air rather than hot, and fuel consumption increases as the ECU runs a richer mixture. A thermostat stuck closed is more serious: coolant cannot circulate to the radiator and the engine overheats within minutes, risking head gasket failure.
Fluctuating temperature readings — the gauge moving up and down rather than settling in the middle — can indicate an intermittently sticking thermostat or air pockets in the cooling system following a coolant leak.
Engine thermostats are usually sold as a kit including the thermostat housing gasket or O-ring. Replace the sealing element at the same time to prevent coolant leaks after reassembly. Drain and refill the cooling system correctly after replacement, bleeding any trapped air from the system. Use the registration lookup to find a confirmed-fit thermostat for your specific engine code.
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Commonly searched OE numbers fitting Engine Thermostat from the TecDoc catalogue.
Common original equipment numbers linked to stocked alternatives.
