The engine gets very hot
Broken or slipping water pump drive belt. Check (see accompanying illustration), adjust the belt or replace it.
The coolant level has dropped. Try to find out the cause of fluid loss. These can be overflow, external or internal leaks - refer to the relevant subsection below.
Note. Never remove the radiator cap when the engine is hot. Wait for the engine to cool down, then wrap the cover with a thick layer of rags and begin to slowly unscrew it. Having reached the first stop, wait for the excess pressure to be released and only then can you finally remove the cover.
Radiator cap defective. Check (see accompanying illustration), replace.
The air passage from the front of the radiator heat exchanger to the rear is disrupted. Blow out the path from the rear side of the heat exchanger with compressed air, or pump it with pressurized water. Faulty thermostat. Check, replace if necessary.
Faulty thermostatic clutch for cooling fan. Replace clutch.
Coolant circulation interrupted. Check and make any necessary corrections.
The setting of the ignition timing is violated. Check, make adjustments.
The patency of the exhaust gas system is broken. Remove the cause of the blockage or replace the faulty section/component.
The layout of the air-fuel mixture is broken. Check as described in the Section on power system troubleshooting), make appropriate corrections if necessary.
The engine oil level has dropped. Stop the engine immediately and add oil to the correct level.
Adjustment of brake mechanisms is broken or "seized" brakes. Check, make necessary adjustments or replace components (see the relevant subsection of the Section on brake system troubleshooting).
The clutch is slipping. Check and make any necessary repairs.
There are leaks from the cylinder head gasket. Check and make any necessary repairs.
The engine is not designed after a major overhaul. Check if the appropriate fasteners are overtightened. Stop the engine and let it cool down.
Note. Overheating of the engine is usually accompanied by steam emissions from the engine compartment. A characteristic sign of a leak in the cylinder head gasket is bubbling of the coolant when the engine is running (see accompanying illustration).
There are external coolant leaks
Loose hose clamp or defective hose (see accompanying illustration). Tighten clamp or replace defective hose.
There are leaks from the radiator heat exchanger, or its tanks. Make any necessary repairs or replace the radiator.
Worn or damaged water pump bearing and/or seal. Replace pump.
Loose or damaged radiator drain plug. Tighten or replace plug.
There are external cracks in the block or cylinder head. Replace defective components.
There are leaks from the thermostat housing or water pump. Replace the failed component.
There are leaks from the heater heat exchanger or through its valve. Make any necessary repairs or replace the defective component.
Note. To check for signs of external coolant leaks, park the vehicle in a clean, dry area and warm the engine to normal operating temperature. Also check for traces of moisture in the car interior under the heater heat exchanger.
There are internal coolant leaks
Leaks occur through the cylinder head gasket due to a violation of the flatness of the mating surfaces (either or both) head or cylinder block. Check, grind or replace the defective component (head/block). Replace gasket.
There are cracks in the cylinder head or block. Replace the failed component.
Note. To check for signs of internal coolant leaks, remove the engine oil dipstick and inspect its blade for signs of oil foaming. Start the engine and observe the exhaust. Excessive steam emission indicates the presence of coolant in the combustion chambers. Check compression pressure (see the relevant subsection in Chapter Settings and ongoing maintenance) to identify a defective cylinder.
Coolant circulation problem
Tension adjustment is broken or the drive belt is faulty (And) water pump. Adjust tension or replace belt (And).
The coolant level in the system has dropped. Top up, check the system for leaks.
There was a partial violation of the patency of the tubes of the radiator heat exchanger. Perform a backflow flush or replace the heatsink.
There is excessive scale buildup in the water passages of the engine. Perform a backflow flush of the cylinder block.
Faulty thermostat. Check and replace if necessary.
The radiator hoses have collapsed. Check and replace defective hoses.
Water pump defective. Replace.
Note. A circulation problem is most easily checked by removing the cap from the radiator and observing fluid turbulence after the engine has warmed up to normal operating temperature.
With a working system, turbulence should occur when the throttle is partially opened. Under the most unfavorable conditions, when there are several faults at the same time, diagnostics can be performed by excluding healthy components during the sequential execution of tests in the order listed.