As a global partner, MAHLE Behr develops and produces thermal management systems and components for well-known automobile and engine manufacturers.

About the product

The demands on our thermostats are pretty tough

MAHLE thermostats work just as well in tropical heat as in arctic cold. They quickly bring each engine to the correct operating temperature by controlling the cooling circuit. MAHLE provides a variety of thermostats and other temperature-regulating components for various requirements:

Thermostat inserts precisely regulate coolant circuits to approximately 20 m3/h in passenger cars, commercial vehicles, stationary engines, as well as agricultural and construction machinery.

Integral thermostats are the ongoing development of the thermostat insert: all components such as the thermostat insert, cover, and gasket are already integrated in the integral thermostat. It can be flanged-mounted directly onto the engine block.

Housing thermostats consist of a cover and a housing i.e. the mixing chamber is already integrated. These thermostats are either completely equipped with hoses or have a flange and hose connectors.

Map-controlled thermostats: an electrical heating resistor is integrated into the wax of the operating element. The operating map of the engine control unit directly regulates it. This in turn controls the engine temperature, which keeps the engine within an optimal range under various loading and operating conditions. The result is more engine output with reduced consumption and emissions.

Sleeve valve thermostats control cooling circuits in large engines with flow rates over 20 m3/h, as found in large passenger cars, commercial vehicles, ships, and locomotives. The relieving of the axial load by the expansion element allows them to function reliably even under heavy hydraulic loads.

Thermocouples are extremely sensitive to heat. They supply data to the electronic control unit about the current temperature level at various points in the engine.

Oil thermostats regulate the oil temperature in automatic transmissions. This shortens the warm-up phase and subsequently keeps the transmission at an ideal operating temperature. This results in reduced wear, improved shifting comfort, and fuel savings of approximately one per cent in conventional driving cycles.

EGR thermostats regulate the coolant flow through the EGR cooler.

Thermal switches protect against engine overheating in stationary vehicles. The thermal switch opens or closes the electrical circuit, e.g. on a radiator fan, at a defined coolant temperature. The thermal switches from MAHLE Aftermarket are designed for an operating voltage of up to 24 V.


Materials: for the safety of people, engines, and the environment—only the best

An expansion element consists of a mixture of wax with precisely defined properties. It is located in a corrosion-resistant metal housing and is the centrepiece of the thermostat. A moving metal piston in the thermostat determines the path that the coolant takes: for a cold start, the piston is in the starting position. The coolant only flows in a small circuit and warms up quickly. At a given temperature the wax melts, its volume increases, and as a result, moves the piston to the working position. The coolant now takes the longer path to the radiator, thus ensuring a constant working temperature. When the heat decreases, the volume of wax reduces, and a spring pushes the piston back into its starting position.

Expansion elements are maintenance-free and durable. Their range of applications is very versatile—there are actuation forces ranging from 30 N to 2,500 N, short or long strokes, and a variety of control ranges within the temperature span of –20°C to +130°C.

The modern alternative for particularly challenging powertrains, for example in hybrid vehicles, is called a map-controlled thermostat.

Individual parts of the thermal expansion element

1. Piston

2. Guide part

3. Supporting disc

4. Rubber insert

5. Expansion material (wax)

6. Case

OE competence

Research and development for the repair shop: so that you can continue to install safe products in the future

Innovative development: the map-controlled thermostat

A map-controlled thermostat can significantly raise the efficiency of an engine. The wax contains an electrical heating element that is activated by the engine control unit. An operating map defines when and how much heat is applied. This makes the thermostat respond more quickly and more precisely—always keeping the engine in the optimal range even under various loading and operating conditions. The result: improved engine output, a longer service life, as well as reduced consumption and emissions. The company Behr Thermot-tronik, acquired by MAHLE, was the first thermostat manufacturer to develop this technology together with a vehicle manufacturer.

Cross section of a map-controlled thermostat with electrical connections and heating resistor integrated in the wax element.

1. Connector plug
2. Heating resistor
3. Valve disc
4. Compression spring
5. Case (operating element)
6. Elastomer insert
7. Working piston
8. Guide (thermostat bypass disc)
9. Housing