8 Signs of a Clogged Radiator

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bad radiator symptoms

After a drive on a hot summer day, my car’s temperature gauge showed a red sign. I waited for a couple of hours before opening the hood as the engine temperature was relatively high after the drive.

A clogged radiator is the most common cause of engine overheating in an older car. If you are driving an old car, you should ensure your cooling system is working correctly.

I checked the coolant level and inspected the hoses for any coolant leaks, but everything seemed fine. Until I saw the bent and distorted radiator tubes, this is when I realized my radiator was clogged.

This article is all about the signs of a clogged radiator, how to diagnose and flush it.

What is a Radiator?

signs of a clogged radiator

In the simplest terms radiator is the central cooling unit of your car. When the vehicle is operating, its engine is burning fuel. The combustion process produces heat. This heat needs to be removed. If heat isn’t removed efficiently, it can cause the failure of core engine components.

The temperature in the neighborhood of exhaust valve and spark plug areas can go beyond 600 degrees celsius. This high temperature can cause irreparable damage to the engine.

The cooling system of your car carries out the function of heat removal. It consists of a radiator, pressure cap, thermostat valve, hose, cooling fan, and working fluid.

The engine coolant starts from the radiator, goes around the engine block, passing through hoses and pipes, carrying away all the heat. This hot coolant returns to the radiator.

The primary function of a radiator is to exhaust the heat carried by the coolant.

How Does a Radiator Work?

The radiator works on the simple principles of heat transfer. A radiator is a series of long tubes connected to each other. When the radiator coolant passes through these tubes, they slow down their speed.

Moving through long tubes at a slow speed gives radiator coolant more time to dissipate the heat it has collected from the engine.

There are three mediums of heat transfer:

  1. Conduction
  2. Convection
  3. Radiation

Heat transfer between radiator and atmosphere occurs through convection and partly via radiation. Through convection, the heat transfer rate is enhanced if the contact area between bulk fluid and the hot surface increases.

For this purpose, fins are located on the outside surface of the radiator. Fins are a medium to increase the rate of heat transfer.

When the car is running, the outside air blows past the radiator fins carrying away all the heat trapped in the hot radiator fluid. However, when the vehicle is standing still, the radiator fan comes on and moves air past the fins.

This is how a radiator works!

What Causes a Clogged Radiator?

coolant and transmission fluid

Following are the leading causes of a clogged radiator:

Car Sitting for a Long time

If you do not use your car for long periods, you can get a clogged or blocked radiator. When your vehicle sits idle in your garage, no fluid runs in radiator tubes. Radiator tubes and fins become a safe haven for dirt and rust particles, leading to blocked radiator tubes.

Radiator Not Serviced

If you have not serviced your radiator regularly or on time, you can get a clogged radiator. Radiator fins are prone to catch dust and rust. If you let this dirt remain inside the radiator tubes, then it is bound to get blocked.

Exposure to Dust and Debris

If you live in a sandy area where dust storms occur every day, you can get a clogged radiator quickly. The dust particles in the air get trapped inside the radiator.

Old Radiator

Even if there is no other cause for a clogged radiator, old cars can have this problem. It is due to the weak cooling system in older cars. The water pump does not operate at total capacity, so it cannot flush the dirt particles properly.

Signs of a Bad Radiator

Following are the most common clogged radiator symptoms.

  1. Engine Overheating
  2. Leaking Coolant
  3. Damaged Cooling Fins
  4. Blockage in Exterior Fins
  5. Broken Water Pump
  6. Cold Lower Radiator Hose
  7. Poor Heater Performace
  8. Physical Changes in Coolant

The clogged radiator symptoms are discussed in detail below.

Engine Overheating

The most basic function of a radiator is to keep the engine cool. If it is blocked or clogged for some reason, it won’t function properly.

The heat produced during the combustion process isn’t removed efficiently. As a result, the engine’s average temperature keeps rising, and you will experience rapid engine overheating.

Leaking Coolant

Coolant leaks are another clear sign of radiator blockage. The whole cooling system of a car is working in a closed-loop.

The radiator is connected to hoses connected to the engine block. Coolant runs past the engine and returns to the radiator. The excess amount of coolant is driven into the coolant overflow tank.

If there is any kind of blockage in the path of the hot coolant, then it will build pressure at those choke points. Since radiator tubes are very narrow, it leaks through tubes and connectors when coolant isn’t allowed past them.

Damaged Cooling Fins

Damaged cooling fins might be an indication of a blocked radiator. The exterior radiator fins are present on tubes. A damaged fin would mean that the tube underneath it has been damaged.

There is a chance that the tube is leaking, and the coolant must be coming out of it, which will cause overheating. Or the outside force on that damaged fin has bent the tube.

Hence, choking of the hot coolant.

Blockage in Exterior Fins

The internal tubes of a radiator can become clogged, but the exterior fins can become blocked too. Leaves, branches, dust particles, and little stones might fly from outside and get stuck in the fins of radiator. These things will hinder the process of heat removal from the fins.

Broken Water Pump

If there is any kind of blockage in the radiator, coolant fluid will not pass through it. The water pump’s function is to pump the coolant through the whole cooling system.

Now, in case of a blockage, the water pump will have to work extra hard to remove the obstacle in the path of the coolant.

If the blockage is removed well and good, if it isn’t, the load on the pump keeps on mounting, and you will end up with a failed water pump.

Cold Lower Radiator Hose

You would need to come out of your car to check this symptom, open the hood, and physically touch the lower radiator hose.

The lower radiator hose is the first and last component in the chain of the cooling system. The coolant fluid starts its journey from here, and after returning to the radiator, it will again go past the lower radiator hose.

If there is a blockage in the radiator, hot coolant will go inside it but never come out. So, the lower radiator hose, which should be receiving hot coolant, will be cold. This is a sign of a clogged radiator.

Poor Heater Performace

The heater core of the car is responsible for the proper functioning of the car heater. If there is a blockage in the radiator, it will not let enough coolant out of it, disrupting the chain of the cooling system.

This will also have adverse effects on the performance of your car’s heater.

Physical Changes in Coolant

The physical condition of the coolant will also say a lot about the state of various components of the cooling system. If the coolant fluid’s color, viscosity, and smell are not normal, then there might be a blockage in the radiator.

The deposits insider radiator tubes are blocking its flow at times. These deposits will enter the coolant fluid and end up contaminating it. The smell of the contaminated coolant becomes pungent, it will become thinner, and its color will get darker.

Open the coolant reservoir and check for any of the above changes.

How To Diagnose a Clogged Radiator?

It would help if you kept an eye on the above symptoms of a clogged radiator. However, you can use the below methods as well to diagnose one:

Method 1# Visual Inspection:

The visual inspection of radiator tubes will tell a lot about their condition. You can take a torchlight, open the radiator fill cap and take a peek inside the radiator. If the tubes are rusty and have deposits all over them, you can be sure that your car is overheating due to a blocked radiator.

Method#2 Replace Associated Parts:

The cooling system of a car is a combination of different components. Before opening up the radiator, you can replace small parts like pressure caps and radiator hoses. This might solve your problem of engine overheating.

Method#3 Uneven Radiator Surface Temperature:

Under normal circumstances, the surface temperature of radiator fins is cold or hot everywhere, depending upon whether the engine is running or not.

But when you have blocked radiator tubes, then at someplace the radiator fins will be hot, and at some places, it will be cold.

This is how you would know that something is wrong with your car’s radiator.

Method#4 Hard to Squeeze Hoses:

When there is no blockage in your car’s cooling system, the radiator hoses are not that hard to squeeze. Since hoses are made out of rubber so naturally, they should become hot and easy to squeeze when the engine is running.

But in case of a blockage, the contaminated coolant is deposited on the walls of hoses, making it very difficult to squeeze.

How to Open a Clogged Radiator?

A simple radiator flush can open a clogged radiator. Flushing the radiator is not a very tough job, you can do it yourself at home. However, if you are dealing with a case of severe engine overheating, then I would recommend you to visit the auto repair shop.

You can find hundreds of videos on how to open a bad or clogged radiator. You can do it by following the steps below as well:

Prepare the Workspace

It would be best if you prepared the workspace for a radiator flush.

First of all, your car needs to be parked on a level surface. And if it is on a deck, then it is better. Because usually, you would need to get under the car.

If your car’s engine was running for a long time, then wait for at least 1 hour before you proceed with the radiator flush. Let the engine cool as the hot coolant might pop out of the radiator cap.

Drain Out the Old Coolant

The next step is to drain out the radiator fluid.

For that, you would need to open the radiator cap.

Then get underneath the car’s engine. There you would find a radiator drain petcock.

Place an empty bucket under the drain petcock.

With a socket wrench, open the drain petcock and let all the radiator fluid out.

Now with the help of a radiator key, loosen the bleed valve. This will release all the water in the cooling system and empty the radiator completely.

Remove the Radiator

For better draining, open the wall mount brackets of the radiator.

Take out the old radiator and proceed to manual radiator flush.

Clean the Visible Dirt

Before proceeding with the flush, make sure to remove any visible dirt on the radiator fins and tubes.

Now replace the drain petcock and radiator cap.

Flush the Radiator

For this step, you would need to purchase a bottle of heavy-duty radiator flush.

Open the radiator fluid reservoir and pour this heavy-duty radiator flush into it.

Now replace the caps of the overflow tank and radiator cap.

Start your car’s engine and let it run for at least 15 mins. In extreme cases of contaminated coolant, keep your engine running for a more extended period.

Open the drain petcock and radiator fill cap.

Let all the hot coolant out of the system, along with all the contaminants.

Replace the Drain Petcock, Radiator Fill Cap, and Radiator

Take a water hose and pour clean water into the radiator.

Fill water until the clear water starts escaping out of the reservoir. This will indicate that your radiator is now free of all deposits.

Fix the radiator in its place if you removed it.

Make sure that all radiator hoses and intact.

Finally, you can replace the radiator fill cap and drain petcock.

Refill the Coolant

Recheck that you have tightened the drain petcock properly. Otherwise, all engine coolant will leak out of the drain hole.

Once you have checked, proceed with refilling the coolant. Fill half of the reservoir tanks with coolant and the remaining half with water.

Check for Coolant Leaks

Inspect the cooling system closely for any coolant leak.

As any leakage can lead to a clogged or blocked radiator again.

Test Drive

Start your car and ensure that all the warning signs are gone.

Not only that, but your ride should be smoother than ever.

Flushing of radiator makes the performance of your engine better.

Average Radiator Replacement Cost

The repair and replacement cost of a radiator would depend upon the make and model of your car. It would also depend upon the type of problem you are encountering. If a radiator flush can clean the tubes, it would go very light on your pocket.

However, if the radiator is done and you need a new one, be ready to pay between $500 and $950. The cost of the radiator is somewhere between $400 and $600. The remaining $100 to $350 are labor costs.

Even the labor costs vary from place to place and car to car. It would also depend on the type of workshop you are visiting, whether it is an authorized dealer’s workshop or a local repair shop.

Minor repair and cleaning services will cost you around $50 to $200. Similarly, if your problem is related to some associated part of the radiator, like radiator cap, radiator hose, or radiator drain petcock, it would cost you $100 to $200.


A radiator is one of the most critical components of the cooling system. It exhausts the heat trapped in the hot coolant. When it goes bad, the functioning of the entire vehicle comes to a halt.

The most common symptoms of a clogged radiator are engine overheating, coolant leakage, and blown head gasket. You could also tell that radiator has gone bad if the coolant changes its color and viscosity.

The exterior fins of the radiator can be blocked, which can cause the engine to overheat. Poor heater performance and a malfunctioning water pump are some other signs of a radiator clog.

If your car’s radiator becomes clogged, you need to replace it. The replacement of the radiator can cost you somewhere between $500 and $950. However, most of the time, all you need is to flush the radiator. You can rinse your radiator by following the procedure mentioned in the above section.

This issue of a clogged radiator can compromise the working of the entire cooling system. So, if you observe any symptoms of a clogged radiator, you need to act immediately. Unclog the radiator yourself or get it replaced by a professional mechanic.

Frequently Asked

What is the average lifespan of a radiator?

Typically it should last the lifespan of your car. The radiator is unlike any other piece of hardware under your hood. The positioning of a radiator is such that the first thing that gets damaged in case of a front collision is your car’s radiator.

Moreover, the radiator is nothing but a structure made out of metal sheets. So, it may catch rust that can reduce its life considerably.

Can a bad radiator cap lead to a clogged radiator?

Yes, a pressure cap is at the head of a radiator. If the pressure cap is not working correctly, it may lead to a clogged radiator. The primary function of a pressure cap is to regulate the amount of pressure inside the cooling system and radiator.

If the average pressure level is not maintained, it will open the way for a clogged radiator. A pressure cap is a very cheap component, but it can lead to expensive repairs if it goes bad.

How often should you clean your radiator?

Car care professionals recommend cleaning your radiator at least once a year. At the same time, my personal opinion is that you should consider cleaning your radiator once after every two years.

Especially when the car is new, you do not need to worry about a clogged radiator. But older cars are already at risk of overheating. Even a partially clogged radiator can pose severe problems to your vehicle.

Hence, it would be best to clean the radiator in your old car more often.

What are the consequences of a bad radiator?

Regular operation of a radiator is essential to keep your car running. If the radiator goes bad, it can disrupt the functioning of your vehicle’s engine. A bad radiator will increase the engine temperature up to alarming levels. A bad radiator can lead to a blown head gasket, cracked cylinder head, or a ceased engine.

How often should you check your coolant?

You should check the coolant of your car at least twice a year. For optimal performance of the engine in summers and winters, maintaining the correct amount of coolant is necessary.

Coolant leaks can reduce the amount of coolant. Otherwise, a car’s cooling system works on a closed-loop basis, and there is no chance for working fluid to leave the system.

Where is a radiator located?

A radiator is probably the easiest part of your vehicle to locate. As soon as you open the hood of your car, you can easily spot a grill structure with long metallic tubes. It is present on the front side of the engine. It is also visible from the front grill of your car.

A radiator is present in such an open position to aid its function. The air from the radiator cooling fan and outside air blows across radiator fins. A radiator is located on the front side of the engine, so there is no hindrance in the path of heat removal.

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