Radiator, Thermostat, and Water Pump Replacement

The components of the radiator are the radiator itself, a pressure or radiator cap, the thermostat, a fan and the heater core which is located in the dashboard of the vehicle - which is actually a small radiator.



The purpose of a radiator is to prevent an internal combustion engine from overheating caused by the friction created as it operates. The radiator uses water mixed with a coolant and also air to keep the engine at a stable temperature. The engine is connected to the radiator through channels. The coolant (usually water based with ingredients to stop freezing, erosion, cavitation and corrosion) is moved through the channels by the water pump. As the coolant passes through the engine it absorbs the heat from the engine. It then passes out of the engine into the radiator where the heat is transferred to fins or impeller blades inside the radiator moving from one side of the radiator to the other side. The fins or impeller blades are exposed to blowing air that lowers the temperature of the liquid. The coolant is thrust outward by centrifugal force where it is sucked into the water pump. This circular process continues as long as the engine is running. To benefit from the airflow created as the vehicle moves forward, the radiator is mounted behind the front grill.


It is important to keep coolant at the recommended level to maintain the engine at the required temperature. If the coolant level falls below the ‘full' mark it is time to add coolant to the reservoir rather than opening the radiator or pressure cap. A mixture of 50% water with 50% coolant is most often recommended and only add coolant when the engine is not running to prevent damage.


Radiator Cap, Pressure Cap or Pressure Release Valve

The radiator or pressure cap or actually the pressure release valve functions like a pressure cooker by increasing the boiling point of the coolant. The value is usually set to 15 psi.



The purpose of the thermostat is 1) to accelerate the warm-up of the internal combustion engine to a specific temperature and 2) maintain a constant temperature of the engine. This is achieved by regulating the volume of coolant mixture that passes through the radiator. The outlet to the radiator is completely shut at low temperatures as the coolant mixture only circulates through the engine block. The thermostat will begin to open as the temperature of the coolant mixture rises enabling the coolant to flow through the radiator. The thermostat will be fully open when the temperature reaches 200 F to 217 F. 


Commonly the thermostat is made up of a heater motor, a valve with a piston set in wax, a flange, a spring, and the frame. The increase in the engine temperature expands the wax moving the piston inside a rubber boot outward thereby opening the thermostat which enables coolant to begin circulating. The reverse occurs when the temperature of the coolant drops - the wax becomes more solid, reducing tension on the spring closing the thermostat. Some radiators utilize a disk that closes and opens. Others have a “check valve” or “jiggle pin” that allow air trapped in the cooling system to move through the thermostat in order to be released from the system. And a few designs use a “bleed notch” or other methods to remove air. 



The fan is a simple but vital component that is controlled by a thermostatic switch or by the engine computer. The fan turns on when the coolant rises above a certain temperature and turns off when the temperature drops below a certain temperature. 


Heater Core

The heater core is actually a smaller version of your vehicle's radiator - it is located deep within the dash of a vehicle. Heated coolant from the engine is pumped through the core. A small fan located in front of the core blows outside air over the heated core warming the air before it passes into the passenger compartment. 


Water Pump 

When the engine is operating the water pump circulates coolant through the radiator, hoses and engine block. It is a basic centrifugal type pump that is belt driven by a connection to the crankshaft or crankshaft pulley of the engine. Its function is to force the coolant to circulate throughout this system.


What can go wrong?

Any of the above parts can develop wear due to the nature of their function. If the radiator has debris in the existing coolant the system will need to be flushed. If there is an oily or sludgy substance floating on the surface of the existing coolant there may be an engine or head gasket leak. 


water pump can fail from contaminated fluid, extensive vibration, or an unbalanced load caused by 1) a bent pulley, 2) an incorrectly installed fan assembly, or 3) a loose or incorrectly torqued mounting bolts which can result in the failure of the shaft.


Heated air from the heater core can slow or stop altogether if the core becomes clogged with sludge or rust. If a small leak develops the cab of the vehicle may fill with white steam or a sweet smell may be detected. Since the core is installed deep within the dash it is labor intensive to repair. 


The technicians at Main Street Automotive Services are highly experienced the in operation of the complex components that make up this system. If any of the issues discussed above occur or you suspect that something is not functioning as it should, give us a call. We will access the problems with your vehicle, provide a free estimate and get your vehicle back to full operation as quickly as possible.


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