Diagnostics of cooling system faults (VW Transporter T4)

Cause	Method of elimination
Too little coolant in the system	The expansion tank must be filled completely to the marking. Check the tightness of the system
Coolant thermostat not opening	Check if the upper radiator hose is warm. If not, check the thermostat, replace if necessary
The water pump is faulty	Remove and check the water pump
Coolant temperature gauge sensor is faulty	Check the sensor
Coolant temperature gauge is faulty	Check the operation of the device at the service station
The expansion tank cap is faulty	Conduct a pressure check at a service station
The water pump V-belt is too loose	Check and adjust tension
Radiator cooling fins are dirty	Blow out the radiator with compressed air from the engine side
The radiator is clogged with scale or rust deposits inside. The radiator is warm only at the top, the lower radiator coolant hose does not heat up	Replace the radiator
The electric fan does not work	Check the reliability of the electrical contacts on the temperature sensor and on the fan motor. Check the temperature sensor. Check the wiring according to the electrical diagram, replace the electric motor if necessary
The circulation pump temperature sensor is faulty	Check the temperature sensor of the circulation pump

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