What causes cylinder head cracks?
1) Overheating
Internal combustion engines heat up very quickly. As the name suggests, they are designed to produce small, controlled explosions.
Much of the energy in the combustion process is actually lost in the form of heat energy, rather than being converted into kinetic energy that powers the vehicle. This is a design side effect that can be mitigated, but never completely eliminated. The most common cause of cylinder head cracks is overheating. When an engine overheats, its components can be stressed far beyond their designed thermal limits.
Most heads are made of aluminum, which can warp or crack if the engine gets hot enough. Engines can overheat for a variety of reasons, most of which are due to defective components in the cooling system. Possible causes include:
2) Air in the cooling system
Air in the cooling system can cause hot spots, causing parts of the engine to get much hotter than the parts measured by the temperature sensor. This is because air cannot transfer heat as effectively as liquid.
If air accumulates around the coolant temperature sensor, it can prevent the temperature sensor from detecting hot spots. You may not realize that your car is heating up until damage occurs.
Additionally, air leaks in the cooling system can cause a loss of pressure within the cooling system. Liquid coolant is more likely to boil at lower pressures.
3) Water Pump Failure
When a water pump fails, coolant can no longer circulate properly through the engine. The coolant in the radiator is cold and fine, but the coolant around the water jackets in the head and block gets very hot.
Without a pump, the coolant can only circulate by natural convection processes, which is too late to remove excess heat before the engine overheats.
4) Thermostat Failure
Internal combustion engines are most efficient when they operate at their designed operating temperature. The normal operating temperature of an engine is hot enough to still burn, usually around 85-99 degrees Celsius. If the engine operates below this temperature, it will consume more fuel, produce more pollutants, and incur wear.
The thermostat shuts off coolant from the radiator until the coolant in the engine reaches its target temperature. At this point, the thermostat opens, allowing ambient temperature coolant to enter the engine, cooling it until it is hot enough to close the thermostat. This cycle continues as long as the engine is running. If the thermostat remains open, your car may run significantly colder, as 100% of the coolant in the entire system will circulate through the radiator, with little chance of it ever warming up completely.
If the thermostat stays closed, the engine will be more susceptible to overheating. Hot coolant cannot be cooled. On some engines, the heater can be used as a mini cooler if needed. The effectiveness of this method depends on the size of the heater core and the wiring of the cooling system.
5) Coolant Leaks
If there are too many coolant leaks, at some point there will not be enough coolant to properly cool the engine. Although a large amount of coolant can be lost before overheating occurs, it’s a good idea to check the expansion tank and radiator regularly to make sure you have enough coolant.
If you notice a coolant leak, check your radiator cap; it’s an inexpensive part, but can have serious consequences if it fails. Keep in mind that not all coolant leaks are visible.