- Hydrometer, commercially available, as well as at gas stations.
Checking the frost resistance of the coolant should be carried out before the onset of the cold season, especially if clean water was added.
Warm up the engine so that the upper hose connected to the radiator is warm.
Carefully open expansion tank or radiator cap, see section "Checking the coolant level".
Draw liquid into the hydrometer and use the float scale to determine the density of the liquid. In our latitudes, frost protection down to -30°C should be provided.