Typical malfunctions of the cooling system are leaks and insufficient cooling efficiency of the engine. The first occurs due to damage to the hoses and their connections, the liquid pump seal, damage to the gaskets, cracks, and the second - due to a malfunction of the fan, breakdowns of the water pump, malfunction of the thermostat, internal and external contamination of the radiator as a result of scale formation.
Signs of a faulty cooling system include engine overheating and boiling coolant in the radiator, unless they are the result of prolonged and heavy engine load or improper adjustment of the ignition system or fuel system.
Thermostat Troubleshooting Algorithm
Note: The indicator pencil is similar to a regular pencil and contains a material with certain chemical additives that provide a given melting point. By applying a pencil mark to the thermostat housing at 88°C and 100°C, you can check the thermostat's operating temperature. These bags should melt when the coolant reaches temperatures of 88°C and 100°C respectively. These temperatures determine the thermostat's operating range. Therefore, if circulation does not occur, this means that the thermostat may be faulty.
(The original material is located on the website: HyundaiBook)