Car Radiator Problems: 8 Most-Common Issues & Solutions

Your car radiator is an air-to-water heat exchanger that keeps your engine cool. If the radiator doesn’t do its job, the coolant in your car can overheat and cause significant damage to the engine, cooling system, and other related components.

The radiator is a simple design, but it has common issues that can affect its ability to work correctly.

We’ve assembled a list of the most common issues you’ll face and the solution to fix each one.

#1 – Your Car is Overheating

The number one issue you’ll have with your radiator is that it causes your car to overheat. This can be seen as your temperature gauge going into the red zone, a red light illuminating in the gauge cluster, or steam wafting out of the engine bay.

Heat is a killer, and it can wipe out your engine completely.

Car radiator closeup

How to Fix It

Overheating can have many causes, but most can be attributed to a lack of coolant or the coolant not being transferred inside the cooling system.

Many parts inside the cooling system need to work together to ensure the coolant that carries heat away from your engine can do that.

If your temperature gauge is reading higher than normal, you may be low on coolant.

Let the car cool down and then open the radiator or coolant bottle cap and check where the level is. If it’s low, add the proper coolant type to the “cold” full line.

If the coolant is full, it may not be circulating within the cooling system. The thermostat may not be opening, the system could have a blockage, or the water pump may not be moving coolant due to a failure.

Each of these issues will be covered separately and what is needed to fix them.

#2 – Your Car Is Leaking Coolant

If you find that your car is low on coolant, that coolant has gone somewhere. You can often find a pool of coolant under your car, and a drip coming from the radiator.

The radiator expands and contracts under the intense heat of the cooling system, and over time it can crack and fail.

How to Fix It

The first step in fixing a leaking radiator is finding the exact spot of the leak. Often the end tanks are made of injection molded plastic that can crack.

The tanks will often develop a small leak where they are secured to the core of the radiator. This metal-to-plastic connection point often cracks and seeps coolant out.

Another leak point is the core of the radiator where the fins are located. There are small tubes in the core that connect each side of the radiator.

These tubes can clog due to debris in the cooling system, and they can also corrode if other fluids than distilled water and proper coolant are added to the radiator. Many car owners add plain tap water to the cooling system by mistake, and the minerals in tap water build up in the tubes causing blockage and corrosion.

It is a more economical choice to replace the radiator if you have a newer car. Older cars may have a limited selection of replacement radiators and you might need to have the radiator repaired or rebuilt by a radiator shop. All of these options will put a clean radiator in your car to restore the cooling efficiency it needs.

Read Also, Why Does My Motorcycle Smell Like Coolant (Solved)

#3 – Your Radiator Shows Signs of Build-Up Inside

Most coolants are colored green, orange, or blue, but over time they can turn a dingy brown if your radiator starts to accumulate build-up inside.

This crud accumulated in the radiator will hurt the cooling efficiency and cause overheating or worse.

How to Fix It

Most car owners don’t make it a regular habit to check their coolant color. It may require removing the radiator cap and using a flashlight to peek into the radiator to see the coolant color.

Others may be able to look at the coolant overflow bottle to get a glimpse of the coolant color. If it’s not a bright green, orange, or blue, your coolant may have contamination that will build up and block your radiator.

Contamination in the radiator and cooling system often comes from corrosion. Most coolants have an anti-corrosion mixture, but it will lose effectiveness over time.

Coolant that is used past its replacement mileage becomes more acidic with age, and that can contribute to corrosion build-up in the radiator.

A secondary cause of build-up can come from transmission fluid that seeps into the coolant. Most automatic transmissions use the radiator as a cooling device to keep the transmission fluid temperature down.

The membrane separating the coolant and transmission fluid often fails and allows the fluids to mix. You may find that the transmission begins to slip as the fluid mixes and damages the transmission clutches.

The best way to prevent long-term damage is to replace the coolant at the manufacturer’s recommended mileage. This can be done with a coolant flush that will replace all coolant in the system, including the heater core inside the passenger cabin area.

You should also check the level and color of your coolant at least twice per year, if not more. Keeping the coolant full and without contamination will prevent long-term damage to the cooling system.

#4 – Your Radiator Fins Are Damaged Or Blocked

Your radiator uses air to dissipate heat from the coolant. The center of the radiator core has small tubes that carry the coolant between the end tanks where the coolant goes into and out of the radiator.

The transfer tubes have small fins to dissipate heat, and if they are blocked or damaged, they won’t release heat effectively.

How to Fix It

Road debris like rocks and bugs can hit the fins in the radiator core and bend them. If enough of the fins are bent or damaged, they can block airflow through the radiator.

The radiator needs this airflow to dissipate heat, and without the airflow, it can cause your car to overheat.

The fins can be restored and unbent using a small screwdriver or needle-nosed pliers. You just need to open them to allow airflow through the radiator core. If the fins are beyond restoration, the radiator should be replaced.

#5 – Your Car Doesn’t Have Heat in The Passenger Cabin

You don’t realize your car’s heater has stopped working until that first cold snap. Your car uses the coolant to transfer heat from the engine into the heater core and then dissipates it into the passenger cabin. If your heater has stopped working, your heater core and radiator may be clogged.

How to Fix It

Your heater core and radiator are similar in design. They both utilize coolant as a heat source and then dissipate that heat into the surrounding environment.

If your heat has stopped working, the heater core is blocked internally or has air trapped inside preventing coolant from circulating correctly.

You can try a heater core flush to remove the debris and corrosion trapped inside the heater core, but it may be a better option to flush the complete cooling system.

If the heater core is blocked with debris, the radiator most likely has a partial blockage from a similar condition. If the coolant flush doesn’t restore the heat in your car, the heater core should be replaced.

#6 – Your Radiator Hose Collapses Causing a Blockage

Your radiator hose should always stay open to prevent a blockage and subsequent overheating. If you notice that your car temperature rises at higher RPMs, the radiator hose could be collapsing.

How to Fix It

Radiator hoses contain a galvanized spring that should prevent long straight sections of hose from collapsing on higher RPMs. If the hose collapses, it will cause a blockage.

The most likely cause of a collapsing hose is a missing spring or a bad radiator cap that is causing a vacuum. Radiator caps are designed to release negative pressure when coolant contracts, but a bad cap won’t allow this to happen. The negative pressure will cause the radiator hose to collapse instead.

The easiest fix for a bad radiator cap is to clean it if it shows signs of corrosion or build-up. If cleaning the cap doesn’t fix the problem, it should be replaced with a new radiator cap.

#7 – Your Thermostat Has Stopped Working

The thermostat in your cooling system opens and closes to allow coolant to flow through the engine. When the engine heats the coolant, the thermostat should open and allow coolant to flow through the complete system.

When the coolant is cold, the thermostat should be closed to prevent circulation. A faulty thermostat will make it appear the radiator has stopped working because the coolant temperature varies wildly.

How to Fix It

A thermostat should keep your engine temperature consistent without wild variation. A thermostat that is stuck closed will prevent coolant from circulating and can cause the car to overheat.

A thermostat that is stuck open will allow coolant to fully circulate at all times, which can cause the car to never achieve operating temperature.

A car that runs too cold may have problem with fouled spark plugs and failed emissions tests because the fuel injection constantly adds more fuel than required because the computer believes the car has not achieved operating temperature.

Poor emissions are a better scenario than overheating, but both have long-term consequences that can be avoided by cleaning or replacing a faulty thermostat.

Corrosion and build-up are the two most likely contributors to a thermostat going bad, and most likely your radiator has a similar corrosion and build-up problem. Be sure to flush the coolant system and replace the coolant as you remedy a bad thermostat.

#8 – Your Water Pump Isn’t Circulating Coolant

Your radiator dissipates the heat carried in the coolant, but without a water pump to circulate the fluid, your car won’t stay cool.

If your car operates at a higher temperature than before, or it reaches an overheating stage, your water pump may have failed rather than the radiator.

How to Fix It

It can be difficult to determine that the water pump has failed without checking if the coolant is circulating.

Many times the water pump seals weep fluid and that is an indication that the pump needs to be rebuilt or replaced. If there are no leaks, but the car overheats, you need to determine if the coolant is circulating correctly.

The easiest way is to remove the radiator cap or overflow bottle cap and watch the coolant with the engine running. If the coolant never moves, the water pump is likely bad and should be replaced.

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