1. Open the hood and inspect the engine compartment. When inspecting the engine, pay attention to the presence of coolant in the expansion tank, the integrity of the rubber hoses, the radiator...
2....and a thermostat.
Note. A broken hose can be temporarily repaired with adhesive tape.
Reinforced adhesive tape is particularly suitable for this purpose (e.g. silver), which can be purchased at car dealerships.
If coolant leaks from under the thermostat housing, tighten the bolts of its fastening. If it was not possible to eliminate leakage by tightening the bolts, then it must be removed, the mating surfaces cleaned and installed on Loctite 518 sealant or its analogues.
3. Inspect the hose connections to the cover and thermostat housing...
4.... as well as with heater radiator pipes. If there is any coolant leakage, replace the hose clamps.
Note. There are two valves in the plug of the expansion tank: inlet and outlet. The exhaust valve plays a big role in ensuring optimum engine temperature. It maintains an excess pressure of approximately 0.14 MPa in the system (1.4 kgf/cm2), providing an increase in the temperature of the start of boiling of the coolant and preventing intense vaporization. Unfortunately, when the valve is stuck in the closed position during overheating, a significant excess of overpressure occurs, which can lead to a rupture of the expansion tank or a break in one of the hoses. In turn, the jamming of the valve in the open position leads to premature boiling of the coolant.
Therefore, once a year, rinse the cap of the expansion tank with running water, and check the valve for sticking. If in doubt, replace the plug. Blow out the radiator cells with compressed air once a year (e.g. from a compressor), directing the jet first towards the oncoming air flow, and then in its direction to remove dirt, adhering insects and road debris from the surface of the radiator. So you can partially restore the efficiency of the radiator.