Cooling system check

Here you will find useful basic information and tips relating to faults in the vehicle cooling system, e.g. engine overheating, engine not warming up, or heating not warm enough.

Cooling system check

In most cases, irregularities in engine temperature or an insufficient heating output can be attributed to faults in the cooling system. Based on the respective symptoms, on this page we will show you which test steps to take in order to quickly identify the fault source.

Important safety information
The following technical information and practical tips have been compiled by HELLA in order to provide professional support to vehicle workshops in their day-to-day work. The information provided on this website is intended for use by suitably qualified personnel only.

 

TABLE OF CONTENTS
Basic principles

Cooling system check and diagnostics
Troubleshooting

Engine overheats
Troubleshooting

Engine does not warm up
Troubleshooting

Vehicle heating does not warm up

COOLING SYSTEM CHECK AND DIAGNOSTICS: BASIC PRINCIPLES

In the event of faults in the cooling system, for example insufficient heating output, engine not reaching operating temperature, or overheating, it is possible to track down the fault cause using simple means. First of all, the cooling system should be checked for a sufficient coolant level, contaminants, antifreeze, and leaks. The V-belt or V-ribbed belt should also have sufficient tension.

 

Depending on the symptoms, troubleshooting can then be continued by monitoring components or recording temperatures as follows:

ENGINE OVERHEATS: TROUBLESHOOTING

Is the displayed temperature realistic?

  • If necessary, check the coolant temperature sensor and indicating instrument ✓

 

Are the radiators or upstream components (condenser) free from contaminants to ensure an unrestricted air flow rate?

  • If necessary, clean the components ✓

 

Does the radiator fan or auxiliary fan work?

  • Check the switch-on point, fuse, thermal switch, fan control unit; check for mechanical damage ✓

 

Does the thermostat open?

  • Record the temperature before and after the thermostat, remove the thermostat and inspect in a water bath if necessary ✓

 

Is the radiator clogged?

  • Check the temperature at the input and output of the radiator, check the flow rate ✓

 

Is the coolant pump working?

  • Check whether the pump wheel sits firmly on the drive shaft ✓

 

Are the overpressure and/or underpressure valves of the radiator cover and/or expansion tank working?

  • If necessary, use the test pump and check whether the seal of the cover is present and/or damaged ✓

ENGINE DOES NOT WARM UP: TROUBLESHOOTING

Is the displayed temperature realistic?

  • If necessary, check the coolant temperature sensor and indicating instrument ✓

 

Is the thermostat constantly open?

  • Record the temperature before and after the thermostat, remove the thermostat and inspect in a water bath if necessary ✓

 

Does the radiator fan or auxiliary fan work permanently?

  • Check the switch-on point, thermal switch, fan control unit ✓

VEHICLE HEATING DOES NOT WARM UP: TROUBLESHOOTING

Vehicle heating does not warm up

Does the engine reach operating temperature or does the coolant get warm?

  • If necessary, first carry out the test steps under "Engine does not warm up" ✓

 

Does the heating valve open?

  • Check the electrical control and/or Bowden cable and valve ✓

 

Is the heating radiator (heat exchanger) clogged?

  • Check the temperature at the input and output of the heat exchanger, check the flow rate ✓

 

Does the flap control work?

  • Check the flap positions and limit stops, fresh-air and recirculated-air function, air outlet nozzles ✓

 

Does the interior blower work?

  • Noise, fan levels ✓

 

Is the cabin filter soiled or air flow rate decreased?

  • Check the cabin filter, check the air ducts for false air ✓