What Does a Radiator Do in a Car?

What Does a Radiator Do in a Car?
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Have you ever popped your car’s hood after a long drive and felt the heat radiating from the engine? As hot as that feels, the combustion chambers inside the engine can reach 4,500 degrees Fahrenheit — nearly twice stainless steel’s melting point. But thanks to your radiator, your engine can withstand temperatures that should cripple it. What does a radiator do, and how does it work? Read on to find out.

What does a radiator do?

A radiator cools the engine using cool air to remove heat from the hot liquid coolant. The radiator is part of a sealed cooling system, and is essentially a heat exchanger between hot coolant coming from the engine and the much cooler outside air. In short, it keeps the engine from destroying itself from excess heat.

Parts of a radiator

A radiator usually gets replaced as a single unit. But there are several key parts to a radiator, and even more in the cooling system. Here’s how it all works together to keep your engine cool.


This is where the cooling happens. The aluminum core is a long series of tubes that carries hot coolant. Heat is dispersed as air flows over the tubes and a dense network of fins. Aluminum is used for both its heat dissipation properties and relatively light weight. By the time the coolant makes it through all the tubing in the core, airflow has pulled away one-third of the engine’s heat.

Inlet/outlet tanks

Modern cars usually have plastic pipes/tanks feeding the core. This is most noticeable at the inlet and outlet. Where the coolant enters or leaves the core, you see the change in material from aluminum to plastic. The plastic has a high strength-to-weight ratio and is great for heat dissipation. But it’s difficult to repair if there is a leak.

Pressure cap

Also called a radiator cap on older cars, this helps improve cooling-system efficiency. Pressure increases water’s boiling point, so a pressurized cooling system won’t boil at 212 degrees. With vehicle engines normally operating between 195 and 220 degrees, the pressure cap keeps the engine from boiling away coolant every time you drive.


Coolant, also often called antifreeze, is the liquid that circulates in the cooling system. It absorbs heat from the engine then releases it in the radiator. Coolant is made up of several compounds, but it’s mainly water. In addition to preventing freezing, coolant also keeps vital engine parts from rusting.

Transmission cooler

A transmission cooler looks like a miniature radiator, with a series of tubes curving behind aluminum fins. It sits in front of the radiator, and works on the same premise—cooler air draws heat from liquid coolant. The difference is that the hot liquid is transmission fluid, which when cooled and returned to the transmission case helps extend transmission life.


Flexible rubber hoses connect the radiator to the engine block. One is an inlet, carrying hot coolant from the engine. The other is the outlet, returning the cooler fluid to the engine for another cycle. If you’re having cooling issues, hopefully it’s just a failing coolant hose. These are cheap and easy to replace.


The thermostat is a small device in the cooling passages that maintains the proper coolant temperature. On startup, the thermostat stays closed, keeping the coolant inside the engine while it warms up to operating temp. The right amount of heat makes the thermostat open, allowing full circulation of the cooling system.

Coolant reservoir

If the cooling-system pressure exceeds the cap’s pressure rating, the excess pressure forces coolant through the overflow tube into the coolant reservoir. Once the system cools down after shutoff, it pulls this reserve fluid back into circulation. In most modern cars, the reservoir is where you add coolant, instead of directly to the radiator.

Water pump

A water pump is an impeller mounted to the front of the engine block. When it spins, it forces coolant through the engine’s passages and the rest of the cooling system. Water pumps are usually mechanically driven, but can be electronically driven in modern cars.

Radiator fans

Cooling fans, or radiator fans, are exactly what the name sounds like. These fans sit behind the radiator and help pull cooler air over the radiator fins, increasing cooling-system effectiveness. The fans sit inside the radiator shroud that also helps direct air. Older cars with carburetors will likely have an engine-mounted mechanical fan doing this task.

How to tell if you need a new radiator

A radiator is critical equipment for every modern vehicle. Attempting to drive with a damaged one will lead to short trips and hefty repair bills. Here’s what it looks like if your radiator is starting to have trouble, or is already on its way out. If you notice any of these things, get your car checked out ASAP.


High temperatures are often the first sign that something is up with your radiator. This is because neglect or unseen damage can lower coolant levels, and then the system doesn’t have enough fluid to cool the engine. You’ll notice the temperature gauge rising and reduced performance. Hopefully, you’ll get a check engine light before anything expensive breaks.

Damaged fins

The aluminum radiator provides greater surface area than flat metal, transferring more heat into the air. If the fins take damage from rocks or a minor fender-bender, the radiator loses effectiveness. A few bent fins are fine. But if you’re inspecting a used car with heavily damaged fins, then keep an eye on the temperature gauge on your test drive.

Leaking coolant

If you notice a puddle of green fluid under your vehicle, you could soon have a radiator issue. The cooling system is sealed, and should not leak. Cracks can happen in the radiator inlet or outlet, or coolant hoses can become brittle and cracked with age.

Dirty/sludgy coolant

Very few systems in a vehicle are maintenance-free. Leave your engine oil in place too long and it becomes filthy and sludgy. The same is true of the cooling system. That coolant, left for years, becomes corrosive. The rust-inhibitors stop working as the coolant starts wearing down the engine’s internal parts. Change this coolant ASAP.

Engine smoke

Low coolant can cause an overheated engine, which causes metal parts to expand at different rates, in turn causing damage like broken head gaskets. Coolant gets into the engine and burns off as sweet-smelling white smoke. This one is serious, so just pull over and turn off the engine. You’ll need to have the car towed to a shop.

How to maintain your radiator

Hopefully, you change your oil to maintain your engine. You’ll follow a similar process to maintain your radiator and extend its service life. When you change your engine oil, take a glance at the engine coolant level. It should be near the corresponding “hot” or “cold” lines on the reservoir, depending on engine temperature. If it’s low, top it up with the coolant type recommended in your owner’s manual. Be on the lookout for leaks.

If the coolant needs to be mixed with water, be sure to only use distilled water. Also check your manual for the radiator drain/refill schedule. If you bought a car without a manual, or lost yours, odds are you are safe with a coolant flush every 40,000 to 60,000 miles.

Frequently Asked Questions

Can a car run without a radiator?

No. If it’s damaged or destroyed in a collision, your car will only run and drive for a very short time. Without a radiator, a car engine overheats, cooks the oil and eventually welds all the hot parts together, destroying the engine.

Does the radiator affect the AC?

The radiator does not affect the air-conditioning system directly because AC operates on a separate system circulating refrigerant. However, the radiator does affect AC because low coolant and an overheating engine cause increased temps under the hood. This in turn overheats the AC system, decreasing the effectiveness of the air-conditioning.

Can you drive a car with a broken radiator?

Driving a car with a broken radiator depends on the severity of the damage. A minor leak can wait until payday if needed. Just keep an eye on the fluid levels, and try any of the inexpensive cooling-system repairs in a bottle. A heavily damaged radiator that lets the engine run too hot is a danger to both you and the vehicle. Don’t drive it until the radiator is replaced.

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At Bumper, we are on a mission to bring vehicle history reports and ownership up to speed with modern times. A vehicle is one of the most expensive purchases you'll likely make, and you deserve to have access to the same tools and information the pros use to make the right decisions.

About Andy Jensen

Andy Jensen is a former reporter, now automotive enthusiast writer. He covers industry news, manufacturing, car reviews, race recaps, maintenance how-tos, and upgrades. Andy has contributed content to Jalopnik, Advance Auto Parts, Carvana, and zeroto60times.com. His project car is a modified Scion FR-S, but he’s probably looking at $400 beaters on Marketplace right now.

Disclaimer: The above is solely intended for informational purposes and in no way constitutes legal advice or specific recommendations.