How Does a Car Cooling System Work?
Cooling systems help keep vehicle engines within a specific operating temperature and prevent overheating. The main parts of a car cooling system are the radiator, radiator cap, cooling fan, water pump, coolant reservoir, coolant, thermostat, heater core, and necessary plumbing to connect these components.
The cooling system's primary job is to remove excess heat from the engine using a liquid coolant. As the coolant flows through passages within the engine block and around the cylinder head, it absorbs the heat generated by engine combustion. It's a cyclical process: the radiator cools down heated coolant before sending it back to the engine block to absorb more heat.
Here's an overview of the cooling system cycle:
- The lower radiator tank sends recently-cooled engine coolant to the water pump.
- The water pump powers the coolant's movement, pumping it through the engine block where it begins to absorb heat.
- Once the coolant has absorbed all the heat it can, and the engine block's temperature begins to rise, the heated coolant is transferred to the radiator. This transfer is regulated by the thermostat, which helps keep the engine operating within an optimal temperature range — usually between 180-200 degrees Fahrenheit.
- When the coolant temperature reaches 180 to 200 degrees Fahrenheit, the thermostat will open to allow the flow of coolant into the radiator.
- Hot coolant flowing through the radiator may be overly pressurized, triggering the radiator cap to divert coolant into the coolant reservoir.
- The radiator then processes the remaining coolant where it is cooled down by the time it reaches the lower tank.
- From there, the cycle begins again.
When you turn on your vehicle's heater in the cabin, some of the hot coolant will be diverted through a bypass hose and into a heater core located inside the car's dashboard. A fan blows air over the heater core, which enters the cabin vents as warm air — this helps alleviate some of the heat inside the engine block.
What Does a Car Radiator Do?
A radiator is the primary heat exchanger in a car's cooling system. Its job is to remove heat from the hot coolant circulating in a car engine and transfer it into the air around the radiator. The radiator sits near the front of the vehicle, typically just behind the grille, so outside air can flow through it to help remove heat.
Each car radiator is essentially an aluminum mesh of tubes and fins. A radiator works because its aluminum body has high thermal conductivity, which quickly absorbs heat from the hot coolant entering the radiator. Hot coolant from the engine block flows into the radiator's upper tank from an inlet hose. If the coolant is too hot and pressurized, a pressure cap on the upper tank will open to transfer some coolant to an overflow reservoir and relieve excess pressure.
The hot coolant then works its way down through the radiator core where the tubes and fins reside. Radiator tubes are flat to maximize surface area contact with the hot coolant, thereby transferring more heat into the aluminum. Heat absorbed by the tubes is then transferred to the radiator fins.
Air flowing through the radiator while driving — aided by a cooling fan behind the radiator — dissipates the heat collected by the radiator fins. Through this process, coolant flowing through the radiator core considerably drops in temperature by the time it reaches the lower tank and gets pumped back into the engine block.
Car Radiator Parts
The main parts of a car radiator are:
- Inlet Hose: Rubber or molded hose that carries hot coolant into the radiator from the engine block.
- Upper Tank: The top section of the radiator where hot coolant first enters from the inlet hose.
- Pressure Cap: A valve used to regulate the pressure of high-temperature coolant as it enters the upper tank.
- Core: A mesh of aluminum tubes and fins designed to remove heat from flowing coolant.
- Lower Tank: The bottom section of the radiator where cold coolant exits through the outlet hose.
- Outlet Hose: Rubber or molded hose that carries cooled-off coolant out of the radiator and into the water pump.
What is Engine Coolant?
Engine coolant is typically a mixture of antifreeze and distilled water. Its primary purpose is to absorb heat around the engine, but it also prevents engine parts from freezing in cold temperatures.
Antifreeze is a chemical solution usually made from either ethylene glycol or propylene glycol. It is a necessary engine coolant component because distilled water alone does not have the temperature range to keep from boiling over in extreme heat or keep from freezing and expanding in extreme cold. The addition of antifreeze increases the coolant's boiling point and lowers its freezing point. Additionally, the antifreeze in engine coolant helps prevent rust and corrosion on vital engine parts.
There are three basic types of coolant available for combustion engines:
- Inorganic Additive Technology (IAT): Made from ethylene glycol and green in color. IAT provides good protection but loses additives quicker than other types of coolant. Replace IAT coolant every two years or 24,000 miles.
- Organic Acid Technology (OAT): Made from propylene glycol and usually orange or yellow in color. OAT coolant lasts longer but is not compatible with other types of coolant. Replace OAT every five years or 50,000 miles.
- Hybrid Organic Acid Technology (HOAT): Typically yellow, green, pink, blue, violet, or orange in color. HOAT coolant combines the protective benefits of IAT with the long life of OAT and should be replaced approximately every five years or 50,000 miles.
Different types of coolant cannot be mixed and vary widely across manufacturers and even between different models from the same manufacturer. Always refer to your Nissan owner's manual for specific requirements on which type of coolant to use with your vehicle.
Bad Radiator Symptoms
Keeping your radiator in good shape is essential to a well-functioning car. Not only can a bad radiator cause your car to overheat unexpectedly, but neglecting radiator issues can also lead to severe engine damage. Watch out for these common symptoms of a bad radiator so you can stay ahead of maintenance and repairs.
1. Visible Leak Under Your Car
If there is a coolant leak coming from your radiator, you may see a colorful puddle on the ground beneath your car after parking. Manufacturers use color dyes in antifreeze such as green, yellow, and orange to differentiate it from other important vehicle fluids. If the liquid also has a sweet smell to it, it is likely antifreeze.
Not all coolant leaks will be visible, so it's best to check your coolant levels regularly. Ensure the engine has cooled completely before observing or opening the coolant reservoir, as hot coolant under pressure can cause serious injury. If you suspect a leak, we recommend getting a cooling system pressure test at a nearby Nissan service center to confirm.
2. Car Overheats Frequently
A car that frequently overheats is often a sign that the radiator is no longer doing its job. A broken or clogged radiator may not be able to cool down or circulate coolant effectively.
If the radiator is not the source of the problem, other cooling system components may be to blame, including a faulty thermostat, broken cooling fan, or low coolant levels.
3. Radiator Sludge
Over time, the coolant in the radiator can become dirty and lose the benefits of its additives. Coolant that is usually green, yellow or orange and may be dark and discolored if contaminated. For cars that have a transmission cooler inside their radiator, the problem may be that some transmission oil has contaminated the coolant and turned it into sludge.
Dirty or sludge-like engine coolant will not move through the radiator properly, leading to blockages and ineffective cooling. Generally, engine coolant should be exchanged every 40,000 miles, but always check your owner's manual for your vehicle's specific radiator exchange interval.
4. Low Coolant Levels
Radiator leaks can often result in drivers having to top up their coolant levels constantly. If you notice your coolant is frequently low despite topping it up, you may have a radiator leak. A pressure test can determine whether or not there's a leak somewhere in your cooling system.
Can a Car Overheat in Winter?
Yes. Cars are just as capable of overheating in the winter as they are on hot summer days. Though colder outside temperatures may mean your engine is slower to warm up, it still gets hot enough to overheat if the coolant is contaminated or not properly circulating. Coolant leaks and broken components, such as a blocked thermostat or failing water pump, can cause your engine to overheat both in summer and winter.
Is your engine not cooling like it's supposed to? Shop replacement radiator parts made just for your Nissan model and year from Nissan Parts, and have your Nissan inspected at your closest authorized Nissan service center.