Your car’s radiator keeps your engine from overheating or freezing. That’s its main job, and it’s an important one (some also keep the transmission fluid at a good temp). Technically, a car can run without a radiator, but the engine would overheat super fast. Learn more about this critical piece of equipment and what to look for when it’s time to replace it.
How Does a Radiator Work?
Your engine produces a lot of heat. Fortunately, coolant keeps it from overheating. As it flows through and around the engine, the coolant absorbs the heat and carries it to the radiator.
When it reaches the radiator, the coolant flows into tubes. The car’s movement forces air through the rows that run between the tubes, cooling down the coolant as it goes. This dissipates the heat through the vehicle’s grille, and then the coolant is run back into the engine to continue cooling it. As long as the radiator is able to dispel heat quickly enough to keep the coolant efficient, the engine is able to run without overheating.
If the radiator isn’t running efficiently, or isn’t adequate for the horsepower being produced, the engine will overheat.
Parts of an Engine Cooling System
In theory, a radiator is a fairly simple heat exchanger. But to function correctly, a radiator needs to be able to pump coolant, store coolant, and exchange heat efficiently. These processes require a few key parts that we'll explain in more detail below.
Radiator Core | Radiator Hoses | Heater Hoses | Radiator Cap | Drain Valve | Fan | Thermostat | Water Pump | Transmission Cooler
The biggest part of a radiator, and the part people think of first, is the core. The core consists of metal tubes surrounded by small fins where the coolant goes to shed heat. The heat is transferred to the fins, which exist between the tube rows.
Cooling fins are usually made out of thin aluminum and aligned to look like rows of small “v”s between the tubes. Fins can become damaged and clogged from insects and road debris, so it’s good to clean them periodically to keep them functional.
Cores come in different sizes and with different numbers of rows. There are a lot of differences in types of cores, which you can read about here.
Radiators have a pretty long lifespan, and should be able to go for 8-10 years without needing to be replaced.
Inlet and Outlet Hoses
The inlet hose takes coolant from the engine and pulls it into the radiator. The outlet hose takes the coolant back to the engine. Despite being the simplest part of the radiator, the hoses are also a radiator’s most vulnerable points. Because radiator hoses tend to endure wear and tear internally, you might not realize they’re degrading until they’re actually leaking.
Radiator hoses typically last about 4 years, but they might need to be replaced sooner depending on use.
Besides getting rid of engine heat, radiators also reroute heat into the cabin for passengers. The heater hoses connect to the heater core under your dash.
Like radiator hoses, you should replace the heater hoses every four years.
A car’s radiator has to stay pressurized so it can circulate the coolant. The radiator cap acts as a pressure valve. When the radiator reaches max pressure, the valve in the cap opens. When the valve opens, heat escapes and excess coolant flows into the overflow tanks. Once it has cooled down, this coolant is pulled back into the radiator.
Radiator caps are set to different densities (measured in psi). Most radiator caps will be set to around 15 psi.
It’s important not to have too much pressure since that could damage the radiator. On the other hand not having enough pressure could allow the engine to overheat. Always use the radiator cap density that’s recommended in your owner’s manual.
Radiator caps should last the life of your vehicle, but you need to check the cap at least once every six months. Just take care when you go to check it. The radiator cap gets incredibly hot, and you should never touch a hot radiator cap.
Not all radiators have a drain petcock, but there’s no doubt this tiny part makes radiator maintenance a lot easier. The petcock keeps coolant from leaking, but it also makes it easy to drain your radiator. Since the petcock is for draining, it’s typically located at the bottom of your radiator.
The radiator petcock should last as long as the core (roughly 10 years).
While not all radiators have a fan, most modern ones do. Adding an electric fan to help disperse heat is one way modern radiators outperform their predecessors. Fans tend to come in two varieties: Those that pull in outside air and those that push hot air out. Pull fans generally work better.
The fan is located in-between the engine and radiator. Usually the fan uses the motion of the engine to turn. Most fans will also have a fan shroud, which helps to keep the heat from the engine from negatively impacting the radiator.
A radiator fan should last the life of your radiator.
Though you want to keep your engine from overheating, you also want to let it warm up. Thermostats keep coolant from flowing into an engine until it has reached operating temperature.
Where the thermostat is housed will depend on the vehicle. For most vehicles, you can follow the upper radiator hose to the thermostat housing.
The thermostat itself is a mechanical valve that uses wax to open and close. When the thermostat reaches its set temperature, usually around 170 degrees, the wax expands and opens the valve. When the engine cools and the wax shrinks, the valve closes again.
The thermostat should last the life of your radiator.
The water pump gets the coolant from the engine to the radiator and back again. This simple device is connected to the engine’s crankshaft. So, as long as the engine’s running, the water pump should be circulating coolant.
The coolant leaves the pump through the lower radiator hose, goes through the engine block, then to the radiator, and then back to the pump.
Water pumps should be able to last between 60,000 and 90,000 miles.
If you drive an automatic, then your radiator probably has a transmission cooler. Though it’s called a “cooler,” it keeps the transmission fluid in its optimum temperature range. That means warming it sometimes as well.
If your radiator contains a transmission cooler, there will be extra cooling tubes for the transmission fluid.
The transmission cooler is not serviceable separate from the radiator, and the two are replaced as a single unit. The transmission lines are also designed to last for the lifetime of your vehicle.
When to Replace a Radiator
Radiators tend to last 8-10 years if they’re properly maintained. People generally only need a new radiator if theirs has been damaged or if they need a more powerful one.
Common Radiator Problems
If your radiator cap goes south, you could have issues with either too much or too little pressure in your radiator. Either problem ends the same way: your engine overheats. In this instance, you could just replace your radiator cap.
Pressure problems can also be caused by leaks, and leaks can be caused by pressure problems. At a shop, they can test the radiator’s pressure to see if this is the issue.
Coolant leaks aren’t just annoying, they’re also dangerous. Antifreeze is extremely toxic, and has killed more than one household pet. If you see a leak, it may not mean you need to replace your whole radiator. Most of the time leaks are caused by older hoses, but sometimes leaks can be caused by cracked radiators, failing water pumps, or other unusual causes.
While a leak indicates that something isn’t working and that you should check your hoses, problems at any point in the cooling system can cause a loss of pressure and subsequent leak.
Rust and Corrosion
What if you haven’t upgraded your engine but it just randomly started overheating? Well, it’s likely due to rust, debris, or other ‘junk’ preventing your radiator from operating the way it should. In this case, you’ll need to flush out your radiator or consider swapping in a new one.
At least once a year, you should make time to clean your radiator as a way of preventing this. You can also invest in an aluminum radiator, which is less susceptible to corrosion.
Upgrading Your Radiator
The other reason to replace a radiator is a lot more fun. As you start adding cold air intakes and tuning your engine, it’s going to produce more horsepower. And more horsepower leads to more heat. To protect your engine you’ll need to improve the radiator to keep up.
When it comes to replacement radiators, you’ll quickly find that you have a lot of options.
Key Features of Car Radiators
There are a lot of factors to consider if you’re purchasing a replacement radiator. Here are some of the top features to consider before selecting a new radiator for your vehicle.
Bigger is better. At least with radiators. A larger radiator will have more surface area which allows for faster cooling. But before you rush out and buy the biggest radiator available, consider this:
- Underhood Space - Engine bays are usually cramped. The more limited the space is, the less airflow you have. That's the opposite of what you want. Pick a radiator that will fit in the space you have available.
- Construction - It’s possible to get more cooling area in a smaller package. Choosing a radiator with more rows or one that's made out of aluminum can give you the same cooling power as a larger unit.
In a radiator, coolant flows through tubes and over fins. Adding rows increases the total surface area fluid can flow over. This usually means faster cooling. Row number needs to be balanced with tube width to calculate for total cooling. A 2-row radiator with 1-inch tubes will cool more quickly than a 3-row radiator with ⅝-inch tubes.
In terms of surface area, sometimes a two-row radiator can cool more quickly than a three row.
One downside to adding rows is that it can make a radiator thicker, which restricts air and reduces cooling capability.
This is one of the many issues that has been helped by making radiators out of aluminum rather than copper-brass. Aluminum radiators can have more rows and wider tubes without adding significant thickness or weight.
Aluminum vs Copper-Brass Radiator Cores
Most radiators are made out of copper-brass or aluminum. Both have advantages and disadvantages.
Radiator Material Pros and Cons
||Easier to repair
Better for endurance
Tends to be larger
|Usually need to be replaced rather than repaired
Copper is a better heat conductor than aluminum, but aluminum radiators are able to cool an engine more efficiently than copper-brass ones. That’s partially because no radiator is made out of pure copper, but rather a copper-brass blend that reduces its heat conductivity.
Brass is used because copper isn’t a very strong metal. Generally, in a copper-brass radiator, the fins will be copper, but the actual soldering points and frame will be brass. Brass has a substantially worse thermal conductivity rating than either copper or aluminum.
Aluminum can also be thinner, which allows for wider tubes in the same space. With wider tubes you can improve your air flow and cooling efficiency.
Crossflow vs Downflow
You can tell the difference between a crossflow and a downflow radiator by the direction their fins are pointing. A crossflow radiator’s fins run left to right, while a downflow’s run up and down. In a downflow radiator, the coolant enters at the top of the radiator and flows down till it exits through the bottom outlet. Crossflow radiators have coolant traveling horizontally from the inlet side to the outlet.
Crossflow radiators typically cool more efficiently. They also fit better in small hood spaces. Downflow radiators were used in many older vehicles. If you’ve got a space set up for a downflow radiator, it will be hard to fit a crossflow in.
What Type of Car Radiator Do You Need?
Now that you know the key features to look for in a new radiator, it’s time to decide which one to go with. There are radiator options for any kind of driver. Which will work best depends on you and your build.
If you’re looking for a replacement radiator for a vehicle with no modifications, the stock radiator is usually the best choice. It’s easy to install, won’t require any modifications, and has already demonstrated its ability to adequately cool your engine.
You may also want to consider a stock replacement for a classic vehicle if you’re trying to be period-correct.
If you’ve upgraded your stock equipment, then you’ll want an aftermarket radiator designed to accommodate more power.
For classics, simply upgrading to a radiator with an aluminum core will make a huge difference. Even when sized to be a direct replacement, they offer better cooling power and lighter weight.
Most vehicles made after the 1980s will already have an aluminum radiator, but increasing rows or investing in a larger radiator can improve cooling power.
Performance radiators can increase your coolant capacity and surface area for faster cooling. While some of these radiators require modifications to fit, they offer major cooling advantages.
What Do You Put in Your Radiator?
The only thing that should go inside of your radiator is coolant. Coolant is a blend of antifreeze and water. In addition to keeping your engine from overheating, coolant also keeps it from freezing. You can learn more about coolant here.
How Much Coolant Do I Need?
The amount of coolant you need varies based on the size of your radiator. Most radiators will require somewhere between 11 and 28 quarts. If you’re not sure what the capacity of your radiator is, you should check the owner’s manual first. If the radiator isn’t original equipment, then you can also drain the radiator and fill it with distilled water in one quart increments to get an accurate capacity.
It’s important to not overfill your radiator. Coolant needs extra space in order to expand and contract in response to temperature fluctuations. When you’re filling the coolant, you’ll notice two marks. The lower mark is for when your engine’s cold. The higher mark is what you’ll use if your engine is hot when you’re adding coolant.
Upgrading Your Vehicle’s Radiator
If you’re increasing your engine’s power, then upgrading your radiator is a great way to protect your investment. Even the most expensive top-of-the-line radiator is cheaper than a new engine.
Check out this guide to radiator installation to get a feel for what your next steps should be.
This article was researched, written, edited, and reviewed following the steps outlined in our editorial process. Learn more about CJ's editorial standards and guidelines.