Attach a control device to the filler pipe of the expansion tank. Using the hand pump of the device, create an overpressure of about 1.4 bar. If the pressure drops, look for a leak where coolant is leaking and fix the leak. If the pressure drops without any signs of coolant leaking or even rises, then it can be assumed that there is a loss of coolant inside the engine, for example, due to a damaged cylinder head gasket or a crack in the housing.
Overpressure relief valve
The safety valve is installed in the radiator cap. Its task is, starting from a certain overpressure, to open the cooling system and thereby create conditions for excess coolant to drain into the compensation tank.
Screw on control device (1) threaded radiator cap (2). Create excess pressure. The safety valve must open at a pressure between 1.3 and 1.4 bar. Otherwise, replace the cover.
Vacuum valve
1. Pull the vacuum valve out with your fingers until it opens. Check if the valve closes completely when released. The vacuum valve in the lid opens at 0.1 bar underpressure.
2. Screw the cap onto the radiator. If damaged, replace the rubber o-ring.
Coolant indicator sensor (diesel engine)
The coolant level indicator system basically consists of a sensor in the compensation tank and a warning light on the instrument panel.
The coolant level indicator when the engine is running warns of too low a coolant level and therefore a possible overheating of the engine. As soon as the ignition is switched on, the control lamp lights up for 30 seconds. When the engine is running, this light will go out immediately.
The coolant level in the compensation tank is removed using a float (551). When the coolant level is low, the contact closes in the sensor (550) and the control lamp lights up. Depending on the driving mode, the warning light first flashes briefly and then flashes continuously. If the control light flashes, add coolant.
Examination
1. Start the engine and leave it to idle.
2. Pull out the plug on the coolant level sensor.
3. Connect an ohmmeter between both pins on the sensor. With the coolant level at the mark "max" the meter should show infinity. With an empty compensation tank, the resistance should be about 5 ohms.
4. Stop the engine.
5. If the sensor is in order, although the control lamp does not light up, check the electrical lines and the control lamp in accordance with the circuit diagram.
Removing
1. If required, drain some coolant.
2. Pry up the safety ring with a screwdriver (550a) .
3. Pull the sensor out of the expansion tank.
Installation
1. Insert a new sensor with a new O-ring (552) so that the protrusions of different widths on the sensor are fixed in the hole of the compensation tank.
2. Press the safety ring.
3. Fill with coolant.