A vehicle’s engine-cooling system serves not just to keep the engine cool, but to also keep its temperature warm enough to ensure efficient, clean operation.
System components include a radiator to dissipate heat, a fan or fans to ensure adequate airflow for radiator cooling, a thermostat valve that opens when the desired operating temperature is reached and a water pump (or coolant pump) to circulate coolant through the engine, hoses and other components.
Most vehicles now employ an expansion tank that allows the coolant to expand, and exit, the cooling circuit when hot, and to return when the car is turned off and the engine cools.
The cooling system also incorporates elements of the cabin’s ventilation system, because engine heat is used to warm the car’s interior.
Coolant
Coolant, technically called engine coolant, is the liquid that circulates through your engine and radiator to maintain the desired operating temperature.
Often mistakenly called antifreeze, coolant is a mixture of water and antifreeze, which is a liquid that prevents not just freezing but also boiling, either of which could cause the engine to overheat.
Coolant is not to be confused with refrigerant, the pressurized gas that allows the air conditioning to keep the cabin cool.
Engine coolant should be checked according to the manufacturer’s recommendation (check your owner’s manual) to ensure there’s enough, and that it’s in good condition.
A replacement interval is also provided in the manual, and it varies with the make and model.
Heater Core
The heater core is a small radiator that warms the car’s cabin using hot coolant from the engine.
The cooling system’s hoses circulate liquid coolant through the heater core as they do through the engine and large cooling radiator behind the vehicle’s grille.
A failed heater core is a common source of liquid in the vehicle’s front foot wells, with steam coming from the air vents or excessive fogging of inside windows.
A sweet coolant odor is another sign of failure.
Replacement costs depend primarily on labor: how easily the core can be removed, whether from the interior or the engine compartment.
Heater Hose
Heater hoses are rubber hoses that circulate engine coolant to and from the heater core, which is the small radiator that provides heat for the cabin.
They typically extend from the engine to the firewall, because the core is located inside the vehicle’s dashboard.
Relatively inexpensive, heater hoses should be kept in good condition to prevent leaks or ruptures that would jeopardize engine cooling.
Radiator/Cooling Fan
The radiator fan (or fans) pulls cooling air through the car’s radiator.
Positioned between the radiator and engine, cooling fans are particularly helpful when the car is stationary or moving at speeds too slow to force air through the grille.
The advent of electric cooling fans, which turn on and off as needed, proved an improvement over engine-driven fans that slow down exactly when they’re needed most.
A failed cooling fan can result in an engine overheating.
These fans sometimes double as a cooling source for the cabin air conditioning’s condenser.
Radiator Hose
Radiator hoses are large-diameter rubber hoses that carry engine coolant between the engine and radiator and back toward the water pump.
Radiator hoses should be inspected as part of routine maintenance to ensure their integrity.
Signs of damage or deterioration call for a precautionary repair that’s much easier and less disruptive than the alternative.
Water Pump
The water pump (technically the coolant pump) is powered by the engine and circulates liquid coolant through the engine cooling system.
Leaks and noise are signs of water pump failure, which can be caused by age and wear or overheating conditions, and are often caused by other faults in the system.
It’s driven by a belt (whether a dedicated serpentine or rarely by the timing belt), so proper belt maintenance is critical to its operation.
Because of its location, it may be wise to replace an older water pump, even if it’s still functioning, while replacing a timing belt because the labor involved is costly.
Radiator
The radiator is Grand Central Station for an engine’s cooling system:
The mixture of antifreeze and water that cools the engine continually passes through the radiator, where it discharges some of the heat it picked up from the engine and takes in cooler air before circulating again through passages around the engine.
A spur line sends warm coolant to the heater core to generate heated air for the interior when needed.
A water pump circulates the coolant around the engine, and a thermostatically controlled fan behind the radiator turns on as needed to draw more air through the radiator to help cool the antifreeze/water mixture.
Though most modern radiators are made of aluminum and plastic and are generally thought to be rust-resistant, the metal can still corrode.
Antifreeze contains rust inhibitors that break down over time, allowing corrosion to damage cooling fins inside the radiator and rust to eat through from the inside and cause leaks.
Radiator (Part 2)
Some radiators also have plastic parts that can develop cracks and leak.
That is why many vehicle manufacturers recommend changing the engine coolant and flushing the system periodically, though in some cases that isn’t for 100,000 miles or more.
Some manufacturers say the coolant never has to be changed and only the coolant level needs to be checked periodically.
Repair shops can test coolant for corrosion resistance and for protection against freezing.
Debris such as dirt, leaves and plastic bags can collect on radiators and reduce their cooling ability.
Hoses connected to the radiator and radiator caps also can develop leaks, and thermostats that regulate coolant flow can fail.
Having a repair shop do a full cooling system inspection should be part of regular maintenance on vehicles more than five years old or that have more than 50,000 miles on the odometer.
Coolant Leak Diagnosis
Coolant, technically called engine coolant, is the liquid that circulates through your engine and radiator to maintain the desired operating temperature.
Often mistakenly called antifreeze, coolant is a mixture of water and antifreeze, which is a liquid that prevents not just freezing but also boiling, either of which could cause the engine to overheat.
The cooling system is composed of various parts: the radiator, pressure cap, fan, pump, thermostat, hoses and overflow tank.
The pump sends cooling fluid to the engine where it absorbs the engine’s heat. After exiting the engine, it runs by a thermostat.
If the cooling fluid is below the maximum temperature, the thermostat stays closed and the fluid is re-routed back to the pump.
However, if the fluid is overheated, the thermostat’s valve opens, routing the fluid through a radiator first.
The radiator cools the fluid by releasing its heat to the air before returning it to the pump.
