Overheating engines happen. To be able to determine the source of the problem is the first step toward a successful repair whether you turn the wrenches or you defer to a professional technician.
First make sure the car is actually overheating. Steam wafting from under the hood does not mean the engine is running hot. Actually, it may not even be coolant that is causing the cloud. It could be leaking motor oil or other fluids that call the engine compartment home. Getting back to the cooling system, a ruptured hose or cooling tube leaking coolant onto hot parts of the engine will create steam and the fix here is replace the failed part, restore the integrity of the coolant and drive on. Had this situation not been tended to, the vehicle would have eventually run hot because of insufficient coolant level.
So there’s the first scenario, low coolant. Symptoms would include a rising temp gauge and lack of heater output as the coolant level goes down the heater core will underperform.
Next, you might have a restriction in the cooling system. The radiator is a likely place for this to happen. Think of the radiator as a giant filter that the vehicle’s cooling fluids (water and coolant) travel through constantly. Contaminants plug the tubes of the radiator and it loses its ability to dissipate heat, which it does by utilizing ambient air blowing against it as the car moves down the highway or by calling on the cooling fans when idling. Generally, this will cause the vehicle to run hotter as you drive faster since the radiator isn’t doing its job.
The function of the thermostat is to get the engine up to operating temperature as quickly as possible by restricting the flow of coolant. However, sometimes thermostats stick closed. This causes the engine temperature to rise rapidly and generally there is also a loss of heat inside the car. Stuck thermostats that are not heeded can blow the tanks of the radiator apart or cause engines to seize.
Lack of air flow through the fins of the radiator will also cause an engine to run hot. Usually there are only two sources for this condition. They are debris collecting on the outside of the radiator or failed cooling fans that aren’t pushing or pulling air through it.
Another cooling system related cause of overheating is a malfunctioning water pump. This is usually the last place professionals look for two reasons. It’s the most difficult to confirm since it requires a labor intensive removal and it happens very rarely.
Cooling system related overheating is the major cause of cars running hot. Internal engine problems like bad head gaskets will also cause overheating and present themselves with their own set of symptoms. Whatever the cause, a rising temperature gauge indicating an overheated engine requires immediate attention.