8 Common Symptoms of a Clogged Radiator You Must Know

8 Common Symptoms of a Clogged Radiator You Must Know

The Role of the Radiator

Something every novice car owner knows is that as an engine runs, it produces a lot of heat. Extended exposure to excessive heat is detrimental to the performance of the engine itself, as well as the proper function and lifespan of every other component located under the hood of your car. Excessive heat is never desirable for any kind of machinery.

To ensure smooth operation, there must be an effective mechanism to keep the engine cool enough. This is the purpose of the radiator, with the help of engine coolant.

A car’s engine uses coolant to absorb the heat and transfers it to the radiator, where the hot coolant cools down by evaporation. Once it cools, the coolant is sent back into the engine and the cycle repeats. In other words, the radiator is a form of heat exchanger.

The safe operating temperature for most cars' engines is somewhere between 195 and 220 degrees Fahrenheit. It’s okay to go a little beyond that upper limit once in a while, especially in warmer months when the air conditioning is much needed. That said, excessive engine heating for an extended period is a big no-no.

Most modern engines are liquid-cooled, using a liquid coolant run through a heat exchanger, which is cooled by air (thus you can say they are actually partly air-cooled). Other engines are air-cooled, using a gaseous fluid instead of the liquid coolant.

What Causes a Clogged Radiator?

The radiator might be clogged due to rust, internal deposit buildup over time, or debris/contaminants getting stuck in the radiator. Such blockages will prevent the proper flow of coolant between the radiator and your engine, thus impeding the radiator’s cooling capabilities.

The most common cause of a clogged radiator is old radiator coolant that has been sitting around for extended periods without being changed, or when the engine hasn’t been running for a while. Old coolant invites sediments and rust that blocks the radiator tubes and fins, impeding the flow of coolant to and from the radiator.

Similarly, a cooling system that hasn’t been serviced and “flushed” regularly would also introduce contaminants that create blockages. You will learn the steps on how to flush the radiator to get rid of or prevent blockages at the end of this guide.

Needless to say, a bad radiator that does not function properly means big, big trouble. A clogged radiator would always lead to engine overheating.

A Liquid-Cooled Cooling System

To intuitively understand the symptoms of a clogged radiator and remember what must be done to fix it, it is important that you grasp how the radiator works.

In a liquid-cooled cooling system, there are interconnected coolant channels running through the engine block and cylinder head. At the top of the cylinder head, all these channels converge to a single outlet.

Pump

The hot coolant is sucked out of the engine to the radiator with the help of a pump. Coolant circulation is maintained as the pump usually sends the heated coolant up through the engine and down through the radiator, taking advantage of the fact that hot water expands, becomes less dense, and is lighter than cool water. Thus, the natural tendency is for hot water to flow upwards and cool water downwards.

The pump is driven by a pulley and belt from the crankshaft. Heat from the hot coolant is transferred into the air, and the now-cooled coolant then returns to an inlet at the bottom of the engine block and flows back into the interconnected channels again.

Radiator Fan

The radiator needs a constant flow of air to “exchange” or transfer the heat of the coolant into the airstream. When the car is moving, this happens anyway. Otherwise, a radiator fan is used to create the much-needed airflow. This fan is driven by engine power.

That said, the fan is not always needed while the car is moving. Thus, to minimize the energy used in running the fan, most cars these days have an electric fan that switches on and off when the coolant temperature reaches a set point, which is detected by a temperature sensor.

Radiator fans in other cars have a thermal fan clutch for optimal cycling. They come with a temperature-sensitive coil spring on the front that expands when the air coming through the radiator is hot enough and reaches a set point. This expansion opens an internal valve that reduces clutch slippage, making the fan spin faster for increased cooling effect.

Without the fan, it is impossible to remove almost half of the waste heat of the engine. The radiator fan is especially important in hot weather, slow driving, or continuous stop-and-go driving. In hot weather, when the air conditioning is on more often, an electric fan is turned on more often and is more prone to failure.

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Hoses, Tubes & Fins

The hoses, tubes and fins of the radiator are parts that are prone to contamination and wear and tear. First, rubber hoses link the radiator to the engine. They route coolant to the radiator to be cooled and then return it back into the engine.

The radiator has a top tank that collects incoming coolant and a bottom tank connected by a core, which consists of many rows of fine vertical tubes. Older vehicles would have vertical tubes, while modern, low-fronted cars have crossflow radiators with tubes that run horizontally.

Sandwiched between the rows of tubes are thin sheet-metal fins. The sheet fins mean the core has a very large surface area, thus when the coolant passes from the top tank through the tubes to the bottom tank, the fins can quickly conduct the heat away from the coolant and dissipate this heat into the cooler air passing through them.

Blocked radiator tubes mean the water pump cannot properly circulate coolant inside the engine block and back to the radiator. Blocked tubes also mean the hot coolant cannot easily flow through them, thus heat from the coolant cannot effectively be conducted away and dissipated into the air surrounding the tubes and fins.

Blocked tubes sound unimpressive but will have a severe impact on the engine’s performance as well as causing other components of the cooling system to start deteriorating prematurely.

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Radiator Cap

At the normal working temperature of the engine, the coolant is just below the boiling point for water. To minimize the risk of boiling, the boiling point must be raised, which is achieved by raising the pressure in the system or pressurizing the coolant.

This pressurization is controlled by the radiator cap that comes equipped with a pressure valve. It is designed to hold the coolant in the radiator under a predetermined optimal level of pressure. When the pressure is too high, the valve opens, allowing coolant to flow out through an overflow pipe.

When the radiator cap does not seal properly, air could enter the cooling system. Air pockets can get inside the heater core, thermostat, and radiator hoses. As a result, the engine will not be able to sustain a consistent and optimal temperature and will start to overheat.

When the engine runs very hot, a cooling system of older vehicles that uses the radiator cap for pressure control would experience a negligible but continual loss of coolant, so it would require topping up of coolant regularly.

More modern vehicles would most likely have a sealed cooling system that prevents such coolant loss. When the engine runs hot, any overflow goes into an expansion tank, then the coolant in the expansion tank will flow back into the engine when the remaining coolant cools down.

While we’re on raising the boiling point, note that the coolant’s freezing point also needs to be lowered to a safe level by adding antifreeze, usually ethylene glycol. This is because water expands when it freezes, and if the coolant freezes, it can burst the block or radiator.

Thermostat

All liquid-cooled cooling systems have a thermostat that sits between the engine and the radiator, usually located above the pump. Its job is to block the flow of coolant to the radiator until the engine has warmed up to its normal operating temperature of about 200 degrees F or 95 degrees C. The radiator is closed off by the thermostat until the engine has warmed up enough, or in other words, the thermostat allows the engine to warm up as quickly as possible. This would reduce engine wear, deposits, and emissions.

The thermostat has a small cylinder located on the engine side. This cylinder is filled with wax that begins to melt at a set temperature, most commonly around 180 degrees F. When the engine warms up, the wax melts, expands and pushes the valve open, allowing coolant to flow through the radiator. When the engine stops and cools down, the wax cools and shrinks, closing the valve again.

8 Symptoms of a Clogged Radiator

Of course, prevention is always better than messing up and fixing it afterward. That said, you must be well familiar with the most common symptoms of a clogged radiator below to detect problems early before expensive engine damage occurs.

Overheating/ High Temperature Gauge Reading

The most obvious symptom of a clogged radiator is engine overheating. The temperature gauge on your dashboard will tell you when this happens. Some newer cars will display the temperature digitally and warn you when the engine temperature gets higher than the safe level.

The temperature gauge is located somewhere in your fuel gauge or your odometer and features a needle that moves between C and H on two ends. If it starts heading towards the red zone on the H, that means your engine is overheating.

Another warning is when the needle of the temperature gauge is sitting noticeably higher than usual. A normal operating temperature for most cars is somewhere between 195 and 220 degrees F. While your engine should typically be operating at around the same temperature with only slight deviations, especially in summer months when the air conditioner is constantly running, noticeable temperature increases should receive due attention.

If you notice a sizable temperature increase for an extended period, a clogged radiator may very well be the culprit. A good flush will usually solve a clogged radiator. At the end of this article, you will learn the proper steps to flush the radiator.

A common question is whether a clogged radiator is the only reason for engine overheating. The answer is: not always. Engine overheating could also be caused when the coolant level is low or a malfunctioning radiator fan or a cap that does not seal properly.

Coolant Leakages

When the radiator is clogged due to severe corrosion caused by contaminated coolant, the cooling fins of the radiator may develop tiny holes or cracks in them, and might lead to coolant leaks. You might see visible coolant leaks on your garage floor or driveway and/or the low coolant level light may illuminate on your dashboard. This is the second most noticeable and common symptom of a clogged radiator.

Radiator corrosion is often due to low-quality coolant or when you regularly add tap water instead of distilled to the coolant mix, as tap water has a lot of contaminants. If a coolant leak is indeed caused by rust, you’ll need to get it repaired quickly because these leakages will get worse with time and can even permanently damage the radiator.

With even a minimal coolant leak, your vehicle will be forced to operate with an insufficient amount of coolant, which means suboptimal performance. If prolonged, your engine may overheat and suffer serious damage that calls for expensive repairs.

As always, check the color of the leaking fluid to make sure that it’s coolant rather than another type of fluid from your car. Most coolant also has a distinct odor that’s rather “sweet”. If it is coolant, try to clean it up quickly because coolant is toxic, and will attract animals to drink it. Diagnose and fix the leak as soon as possible or at the very least keep the coolant level topped off to keep your engine running for the time being.

Do note that if your radiator is leaking because of severe rust, a thorough radiator flush will not be able to repair this problem. The radiator might be failing altogether and you may have to replace it.

However, having said that, if a radiator flush is not regularly done, the system will more likely be prone to rust and blockages.

Change in Coolant Colour, Viscosity & Smell

Another symptom of a clogged radiator is changes in the characteristics of coolant, which most likely means it is contaminated. During your regular maintenance, you should make a point to inspect the coolant, see if it needs a refill and check its color, viscosity, and smell.

Coolant should be a bright green or yellow color. There are other colors of coolant out there including pink, blue, and purple, just make sure you’re aware of the color of your coolant. Coolant is typically of a certain thickness that would allow it to flow freely inside the cooling system.

Over time, internal deposits, sludge, or external contaminants (like from tap water) can contaminate the coolant, typically turning it into more of a rusty color. Because it’s contaminated, it’s going to be much thicker than normal, which will cause it to flow more slowly and create blockages.

To check the color and viscosity of the coolant, the easiest way is to check the coolant overflow tank (you should have a coolant overflow tank that you can easily access and quickly inspect). If you see a drastic change in color and/or thickness, you’re going to need to thoroughly flush the system to prevent clogging the radiator.

In addition to the change in color and viscosity, coolant should have a distinct sweet smell, contaminated coolant would smell a bit like rubber.

A side note: some vehicles have a transmission cooler located within the radiator. If a leak occurs in the barrier that separates the two, the coolant and transmission fluid would mix and cause double the trouble.

Exterior Radiator Fins Blocked

Radiator fins can block the airflow due to various reasons, one of which is clogging due to foreign material building up on these fins. You should be able to see the radiator fins at the front of your radiator. Because they are outside and exposed to the air, these fins can easily become clogged with dirt, road dust, and even small branches or leaves and insects.

If you see white crusty deposits corroding these fins, they are clogged. These clogged fins are blocking the airflow and not allowing the coolant to cool down effectively.

Fortunately, if it’s the fins that are clogged with debris and contaminants, you’re likely able to spray them clean with a garden hose. On most cars, it should be quite straightforward to remove a plastic cover or two to get access to these fins located on the front of the radiator.

Bent or Damaged Fins on the Radiator

Radiator fins are extremely thin and delicate. They can get bent from physical contact with foreign material while the car is in motion. When enough fins get bent or damaged, they will flatten against the radiator. This will restrict airflow, thus impeding your radiator’s ability to keep things cool and cause engine overheating.

A negligible physical contact, like a piece of tiny gravel hitting the fins while driving, or even when spraying water to clean off the fins using a strong pressure washer, or anything else banging into the fins can cause damage. Damage can also occur during radiator removal and replacement.

Leaking or Damaged Head Gasket

A clogged radiator will most definitely result in engine overheating and if prolonged cause serious engine damages such as a leaking or blown head gasket or a cracked cylinder head. These damages are expensive and troublesome to repair.

In addition to rapid engine overheating, a damaged head gasket or cylinder head will manifest as rough running of the engine, white smoke coming from the exhaust, and excessive use of coolant.

Heater for Passenger Area Not Working

The cabin heater of your car relies on passing the hot coolant through the heater core and then using a blower fan to blow the resulting hot air into the passenger area. A clogged radiator means not enough hot coolant makes its way to the heater core for warming up the cabin.

Although improper working of the heater is among the common symptoms of a clogged radiator, do note that a bad thermostat is more likely to be the culprit.

Water Pump Malfunction

As stated above, the most common cause of a clogged radiator is old engine coolant that gets contaminated. Contaminated coolant loses its lubrication and anti-corrosive properties. This can result in damage to the engine’s water pump, which leads to improper circulation of engine coolant.

Radiator Repair Cost

Radiator Flushing

Radiator hoses, and hose connections are prone to corrosion and sediment buildup over time, which can result in cracks or holes in the radiator. Replacing the radiator hose could cost you only around $30 to $60 and this is a comparatively easy job that you can actually do yourself.

If you’re