Checking the air preheating device (Renault 19)

Bimetallic valve (arrow on the left picture) in the intake manifold of the Bosch single-point injection system reacts to the temperature of the intake air - and creates an intake vacuum in the membrane (2 - right picture) of the intake manifold on a cold engine. If the intake air becomes warmer, the bimetallic valve opens, the vacuum transmitted to the membrane decreases, and the valve (1) closes and opens access to cold air. If you think that the bimetallic valve is faulty, you should check the connection of the pipelines under the vacuum, as well as for kinks and cracks.


1. This check should only be carried out on a cold engine, as the wax thermostat starts to operate at a temperature of +26°C.



2. On a cold engine, the valve should be positioned so that warm air can enter the engine.

3. Warm up the engine to operating temperature.

4. On a warm engine, the valve should be positioned so that only cold air enters the engine.

5. If this is not the case, check if the valve moves easily.

6. If the valve does not work, it is necessary to replace the entire air filter housing.

Note. Recommendation: to check the functionality of the wax thermostat, you need to warm up the sensor with warm air from a hair dryer - then the valve flap should move relatively quickly inward. Drop some water, and the valve should also quickly close. If there is no movement, then the thermostat is faulty or blocked by the valve from below.