What does a car radiator do?

Don’t get hot under the collar wondering what a car radiator does – read our guide to find out

Petrol and diesel cars are fitted with all manner of auxiliary components in addition to the engine itself. From power-steering pumps to air-conditioning condensers, engines are surrounded by an ecosystem of engineering.

One of the most important subsidiary components of an engine is its cooling system, and a car’s radiator plays a crucial role in this.

This guide will talk you through what a radiator does, how it works, how you can tell if you have a problem with you car’s radiator, and how much a new car radiator might cost if you need to replace yours.

What is a car radiator?

Most of us are familiar with the radiators present in houses, which radiate heat to warm our rooms. But while a car radiator also radiates heat, it does this because car engines create wasted heat when they ignite fuel, and this heat needs to be radiated away from the engine to prevent it from overheating.

How does a car radiator work?

A car’s engine has what is known as a ‘water jacket’ around it. This essentially comprises holes and channels that run inside the engine block, separate from the combustion chambers. Coolant – a blend of chemicals and water – is circulated through this water jacket by the engine’s water pump, with the coolant absorbing heat from the engine as it passes through.

This heated coolant is then pumped through a series of hoses to the radiator, which sits at the front of the engine and is comprised of a series of tubes connected to ‘fins’ – thin metal strips that create a large surface area for the heat to dissipate from and head off into the atmosphere, rather than remaining in the engine.

This cooling effect is enhanced by the movement of air across the radiator as the car is driven, while a fan is automatically activated to create moving air if there is not enough; this often occurs if the car is stuck in traffic, or parked up and running on a hot day.

Conversely, when the engine is started from cold and needs to warm up in order to reach optimal operating temperature, a valve known as the thermostat will stop the coolant from reaching the radiator, leaving it circulating around the engine block until the engine is hot enough.

How to tell if your car radiator is broken

Because an engine’s cooling system is made up of several component parts – from the radiator and thermostat, to the water pump and cooling fan – specifically diagnosing a faulty radiator is not always straightforward unless you are mechanically trained or minded.

One symptom of a clogged, damaged or otherwise faulty car radiator people often spot, though, is that their engine is overheating; this will be indicated by a warning light or message, while the temperature gauge on the dashboard will be reading high.

Another symptom is damaged radiator fins: if you are able to see the front of the radiator, look for dents, holes or creases in these, and also keep an eye out for any damage to the rest of the radiator body.

You may also notice a coolant leak from the engine, either because you see dripping, or because you get a warning light for low coolant – though there may not be an easy way to tell if the leak is from the radiator, or from another part of the cooling system, such as a hose.

Safety warning: if you have a coolant leak and have no alternative but to drive the car before you get it fixed, you should top up the coolant to reduce the chances of the engine overheating. This must be done only when the engine is cold. Opening the radiator or its expansion tank (which helps reduce excess pressure in the system, and is typically where more coolant is added) when the engine is hot poses a risk of very hot coolant escaping under pressure, posing significant risk of injury.

Do note that dripping from the bottom of the car is not always a problem: air-conditioning systems need to disperse collected condensate (water) from time to time, so don’t automatically assume the worst if you spot a wet patch under the vehicle – though do investigate it. Air-con systems tend to do this from the bottom of the rear of the engine and their condensate is clear water; coolant, on the other hand, is often coloured yellow or pink.

How to fix a broken car radiator

It may be possible to repair minor radiator leaks with a dedicated leak-plugging repair liquid, which is poured into the radiator and solidifies around small holes or cracks. The jury is out on how effective such products are, with anecdotal reports indicating they can leave sludge in the cooling system, affecting its operation. A proper diagnosis and repair by a qualified technician is far preferable to this.

There is also a homespun fix/rumour that involves cracking an egg (minus shell) into the radiator, with the idea being that the yolk and white will lodge in leaks as they cook and solidify. This is very difficult to recommend unless the leak is a matter of life and death, as chances are the egg will find its way into parts of the cooling system where an egg has no right to be, causing untold issues.

In general terms, a proper mechanical repair of a broken radiator by a qualified technician is not often not economically viable, as any such repair is likely to take a significant amount of time, and replacement car radiators are relatively inexpensive.

How to stop a car radiator from breaking

Maintenance, maintenance, maintenance. It may be nigh on impossible to stop a stone being flung up and damaging your radiator, but aside from accidental damage, taking proper care of your car and its cooling system will give you the best fighting chance of keeping it in good working order.

Follow the car manufacturer’s recommended maintenance schedule, having the coolant renewed at the appropriate intervals. Coolant flushes, which see the old coolant drained, and a cleaning liquid run through the system before new coolant is added, may also be recommended.

Also be sure to regularly check the coolant levels in your car, alongside other checks such as oil, brake fluid and power steering fluid levels.

How much is a replacement car radiator?

It is almost mandatory that every question about cost surrounding cars begins with the answer ‘it depends’, and this is true when it comes to how much it costs to replace a car radiator.

Your garage’s hourly labour rate will determine part of the costs, while the price of a replacement radiator for your specific car is another factor. What car you have also comes into play, as some radiators are easier to access and remove/replace than others.

As an indication, a new radiator can cost £80 or so for a mainstream car, while allowing an hour and a half’s labour for draining the system and replacing the radiator is not unreasonable. Factor in the cost of a system flush and garage rates for new coolant, and budget of £350 or so wouldn’t be unreasonable.

Do electric cars have radiators?

Electric motors and batteries are way more efficient than petrol and diesel engines, and generate very little heat when running, hence there is no need for a radiator as there is in a car with an internal combustion engine. EVs do have thermal management/cooling systems for their batteries though, which need to be kept at optimum temperatures during charging and use. These often use coolant (though some are air cooled) and may have small radiators as part of the cooling system, but checking and maintaining EV coolant systems is the job of a trained technician. Some EV coolant systems are also designed to last the life of the car, while others involve the battery cells themselves being soaked in an low-conductivity liquid coolant.

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