Radiator Malfunction: Failure & Symptoms (Here Is How To Fix)

Radiator Malfunction

When something goes wrong with your car it’s always a very worrying experience, and it can be very expensive and time-consuming to get back on the road again.

If you’re concerned that you might have a radiator malfunction and you want to know what to do about it, we’ve got the answers you need.

The radiator in your car is responsible for removing heat from the engine, and it’s essential for the vehicle to function safely and efficiently. It can malfunction in many ways, such as springing a leak, becoming clogged, or becoming damaged from rust or general wear.

Here are a few steps you need to take to fix radiator problems or malfunctions:

Step 1: Check for leaks.

Step 2: Inspect the coolant.

Step 3: Check for rust and damage

Step 4: Check the fan

Step 5: Check the water pump and thermostat

What Is The Radiator In Your Car?

Before we get into the details about what might have gone wrong with this piece of kit, we first need to understand what it is and how it works.

The radiator in your car is like any other radiator, in that it exchanges heat from one place to another. Unlike the radiators in your home, however, it is designed to remove heat rather than produce it – in order to keep the engine in your car cool.

It looks like a rectangular metal box – with a face that’s covered in thin metal fins and backed by a honeycomb pattern.

Behind this, and contained within the radiator, you will find a fan – and the whole thing is connected by a series of hoses that move coolant through the system.

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How Does The Radiator Work?

In the most basic terms, your car’s radiator takes heat from the engine and disperses it so that the engine cools down.

To do this, it is part of a cooling system that sends liquid around the engine to absorb the heat that it is generating, then brings that hot liquid to the radiator. Then, the radiator blows cool air across the liquid to cool it down and release that heat outside.

What that means is that there is more than one element involved in the typical cooling system for a vehicle, which means that there are a lot of parts that can go wrong. These components usually include:

  • The galleries: that are cast into the cylinder head and engine block and circulate liquid around this area to absorb heat and take it away.
  • The radiator: which contains many small tubes that contain a honeycomb pattern and thing fins that enable them to quickly disperse heat. This is where the hot liquid from the engine comes to cool down.
  • The water pump: that circulates your coolant liquid throughout the system.
  • The thermostat: that monitors the temperature and increases or decreases the amount of coolant going to the radiator accordingly.
  • The fan: that draws in cool air through the radiator.
  • The pressure cap: that keeps the system under pressure, allowing the coolant to travel efficiently.
  • The inlet and outlet tanks: that store the coolant before it is sent to the engine and receive it when it comes back again.
  • The hoses: that the coolant travels along.

With all of those different parts in mind, you can start to see why it can be so hard to diagnose exactly what might be causing a radiator malfunction, and why it can be a tricky problem to fix.

What Are The Symptoms Of A Bad Radiator?

So, how can you tell that there might actually be some kind of problem with your radiator that needs your attention?

Well, there are a few common symptoms of a radiator malfunction, and some of them are more obvious than others.

  1. Overheating. The first thing that you will probably notice is that your temperature gauge will start reading as higher than normal, which means that the coolant in your engine is getting too hot and isn’t able to cool down the engine the way that it’s supposed to. This should be a particular worry if you’re overheating while the car is idling and not on the road.
  2. Leaking. Another classic sign is a small puddle of coolant underneath where the engine is housed. Leaks are one of the most common radiator issues, and they can happen almost anywhere along the system.
  3. Low coolant levels. The “low coolant” warning light on your instrument display is another sign that there may be problems with your radiator, particularly if it is happening more often than usual. If you’re having to top your coolant up too much then it may well be leaking out somewhere.
  4. Coolant changes color. The coolant that you put into your car should have a pretty bright color – often blue, yellow, orange, red, or green. If you notice that it has become much darker or seems thicker than normal, then this might mean that contaminants are building up within the cooling system.
  5. Rust or damage. This is a symptom that you probably won’t notice unless you go looking for it, but any kind of damage or deterioration to the metal fins of the radiator itself can lead to serious problems throughout the whole system.

How To Fix A Radiator Malfunction

If you spot any of these malfunctions with your radiator, then it’s time to get involved and try to find a solution.

Depending on what has actually happened, then there will be different fixes that you might need to implement.

We’re going to walk you through the steps that you can take to identify the exact problem your radiator is having, what you should do once you’ve found it, and how much it might cost.

Step 1: Check for leaks.

The first thing to look for is leaks within the cooling system. This is the most likely culprit, and it can be quite simple to fix.

You need to investigate every component of the system. Start with the hoses, particularly where they connect, but make sure to have a look underneath the core radiator itself.

It may be that the hoses have degraded over time, or they have simply become loose. You might see the brightly colored coolant fluid or notice a sweet smell.

Fix: You may be able to just tighten up the connection points to solve a leak, but it is more likely that you will need to replace the old hose entirely. If the leak is inside the main radiator, however, that will usually require a professional to get it fixed.

Cost: A new hose normally costs between $100 and $200, while repairs on the radiator can range from $200 to $1000 if it needs fully replacing.

Step 2: Inspect the coolant.

If there aren’t any leaks in the system, then you should take a look at the coolant fluid itself. If it is a darker color or has become thick and viscous, then mineral deposits have started to build up in the system.

You should also make sure to take a look at the radiator itself and the hoses to see whether any debris or gunk has built up there.

If you don’t solve this too, then the new coolant will continue to become contaminated every time you top it up.

Fix: First, clear out any grime or dirt from the radiator and the hoses. Then, you can flush the cooling system to remove the old, dirty coolant before filling it with fresh liquid.

To do this:

  • Place a pan or bucket under the radiator drainage valve.
  • Open the drainage valve and allow the old coolant to drip out.
  • Flush the system by topping it up with clean water, then start the engine and let it run for 15 minutes.
  • Drain the water from the system.
  • Finally, add fresh coolant to the reservoir.

It’s recommended that you flush your cooling system every 3 to 5 years, or around every 30,000 miles.

This will help to remove harmful deposits, provide better lubrication, and improve corrosion and temperature protection for the engine.

Cost: Flushing the system yourself can be pretty inexpensive, but you can also get it done by a professional for as little as $40.

Step 3: Check for rust and damage

If there are no leaks in your cooling system and the coolant fluid itself is clean, then you want to check the major components for any damage – particularly to the radiator itself.

Damage to the hoses or connectors will typically result in leaks, while damage to the radiator will make it less efficient at dissipating heat.

Rust can cause deposits to appear in your coolant fluid, but it can also erode away at the metal and create holes.

Additionally, the fins on the front of the radiator might have become bent, which means that they will trap in the air rather than allow it to leave the system.

Fix: This is a problem that can generally only be solved by repair or replacement. If there is significant damage to the radiator in your car, then you may need to replace it entirely.

Cost: Minor repairs can cost as little as $200, but you may need to spend as much as $1,000 if you need a new radiator block.

Step 4: Check the fan

This can be more difficult to check, as the fan itself will be hidden inside the radiator itself. If you’re getting a red temperature warning on your dashboard and the radiator itself looks safe, then it is likely a problem with the fan. If it’s damaged then it will need replacing, but it might also be a technical fault.

Fix: Try replacing the fuse, which you can find by looking at your vehicle’s manual. If that doesn’t work, then the temperature sensor may be faulty, the relay may be defective, there might be a problem with the motor, or there may be a wiring issue.

In most of these cases, the part will need to be replaced.

Cost: Replacing the entire radiator fan will usually cost between $500 and $700, but smaller, individual components will be cheaper.

Step 5: Check the water pump and thermostat

If there is nothing else wrong, then the problem is likely with your water pump or your thermostat. These can be difficult to troubleshoot yourself, so it may be best to call in a professional at this point.

Fix: Issues with these components can generally only be solved by replacing them.

Cost: A new thermostat often costs around $200, while a new water pump can go for anywhere between $300 and $700.


So, what is a radiator malfunction and what do you need to do about it? If your radiator is not working properly, then your engine can overheat.

You might notice that the temperature gauge is reading higher than normal, particularly when you’re idling, or you might spot signs of leaks, deposit build-up in the coolant fluid, or damage to components in the system.

To fix it, you may need to flush the cooling system or you might need to repair or replace the components that have become faulty.




Steve P.

Steve is an automotive technician, technical writer, and Managing Editor. He has held a lifelong passion for cars, with a particular interest in cars like the Buick Riviera. Steve is based in Boise, Idaho.

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