Common Bad Radiator Symptoms

The radiator helps cool the coolant in the cooling system. If the radiator is failing, it can cause engine overheating and coolant leaks. This article covers 5 common bad radiator symptoms, some pro tips for repairing a radiator, and how to replace a radiator yourself.

Fix a bad radiator yourself with quality auto parts at 1aauto.com

5 Signs of a Bad Radiator

Symptoms of a Radiator Leak

  • Engine overheating—engine’s temperature noticeably rises on the temperature gauge
  • Coolant collects in a puddle underneath the radiator
  • Coolant is leaking from the radiator

Symptoms of a Bad Radiator

The radiator supports and cools the coolant in the cooling system that cools the engine. The normal operating temperature on most vehicles is between 195 and 220 degrees. If the engine temperature rises above that temperature and the coolant fails to cool it down, the engine will overheat.

In a lot of cases, the radiator also cools the transmission fluid. Since unrestricted air needs to flow through the radiator, it’s placed at the front of the vehicle behind the grille.

Radiators can suffer several problems. Some problems are particular to their construction material and others are universal. Below are 5 common symptoms of any bad radiator.

1. A Clogged Radiator is a Bad Radiator

New coolant (left) and contaminated coolant (right)
New coolant (left) and contaminated coolant (right)

The most common sign of a bad radiator is a clogged radiator. Coolant should be a blue or green color and about the same consistency as water. Corrosion inside the radiator can cause rust to enter the coolant, turning it into a yellow or brownish sludge. This sludge flows more slowly (being, as it is, sludge), and cannot cool the engine as effectively.

Engine overheating may be a sign of a clogged radiator. The sludge can also stay in the corners and leave mineral deposits, which can impede the flow of coolant and reduce the cooling capabilities of the radiator. Clogged radiators can also develop further corrosion, which can eventually lead to leaks. Change the coolant at regular intervals, as described in your owner’s manual, to avoid further corrosion.

2. Damaged, Punctured, Rusted, Clogged, or Leaking Cooling Fins Can Cause Bad Radiator Symptoms like Overheating

Bent and damaged cooling fins
Bent and damaged cooling fins

One way to tell if a radiator is bad is to look at the fins. Occasionally, radiators will develop problems from the outside rather than the inside. The exterior of the radiator can be damaged by rocks or other road debris. This can lead to punctures and leaks, or to bent or broken fins. Since the fins’ purpose is to increase the surface area of the radiator and radiate heat away, damage to the fins significantly dampens the radiator’s effectiveness. If the cooling fins are clogged or blocked, there’s going to be an issue with the radiator.

Debris collected on the radiator fins
Debris collected on the radiator fins

Luckily, a tool exists, known as a radiator comb, that can help straighten out bent fins. This will not help, though, if the fins are totally broken.

Rust and corrosion can also affect the outside of the radiator, leading to leaks or decreased effectiveness of the radiator fins. The fins are also made of aluminum, which is a soft metal. Sometimes the fins can bend. The fins can also fall apart and separate.

Keeping up with cooling system maintenance, like flushing the system or spraying out the fins with a garden hose, can extend the life of the radiator.

3. Cracked Plastic Tanks or Leaking Seals Can Cause Bad Radiator Symptoms

Tank and seal disconnected from a radiator
Tank and seal disconnected from a radiator

Cracked or broken tanks that leak or leaking seals on the radiator are symptoms of a bad radiator. The plastic tanks on the radiator may be on the top and the bottom or on the sides. The tanks will be filled with coolant, so they have a seal between the aluminum and the plastic tanks.

If there is an overheating condition that heats up the coolant, causing it to expand, which increases pressure in the cooling system, the plastic tanks can crack under that pressure.

Transmission lines running through a tank on the radiator
Transmission lines running through a tank on the radiator

The seal is also capable of leaking. Seals can break down, and contaminants in the system can break them down faster. For example, if the transmission lines run through the radiator and leak, the contaminated coolant can eventually break down the seal.

4. Corrosion is of a Symptom Bad Radiator

Corroded radiator hose and hose clamp with white deposits
Corroded radiator hose and hose clamp with white deposits

On rare occasions, more unusual problems can occur. If the ignition system is not properly grounded, the radiator may receive an electric charge. In aluminum radiators, this will cause electrolysis. In this situation, an electrochemical reaction between the aluminum and the coolant will cause rapid corrosion of the aluminum.

Aluminum may also react poorly with old cooling additives. These were designed with copper and brass radiators in mind and can cause a reaction that will eat away at the inside of the radiator. Copper tubes, because they are not as strong as aluminum, can blow out under pressure.

5. Broken and Bad Radiator Parts

Broken radiator parts could be symptoms of a bad radiator. All related cooling parts can also suffer damage and keep your cooling system from operating properly. For example, the hoses can develop leaks or kinks that keep the coolant from flowing properly. Radiator hoses can suffer abrasion or punctures from road debris, can deteriorate due to overheating and can react to oil leaks. Oil interacts with rubber in strange ways and can make the hose become spongy or gooey and develop bulges. Looseness or deterioration of the hose clamps can also cause leaks at the connections.

A malfunctioning radiator cap can also cause problems. A cracked cap can lead to leaks. A problem with the plunger (usually attributed to corrosion of the metal spring) can lead to coolant boiling at a lower temperature and being lost to evaporation.

The overflow tank can also develop cracks and leaks.

5 Pro Tips for Replacing the Bad Radiator

1. Do Not Open the Cooling System When Hot

You do not want to open the cooling system when it’s hot. If you notice the radiator cap is hot, do not remove it until the system is cool. The hot coolant under pressure could spray up with the cap removed and burn a bystander.

2. Flush the Cooling System Before Replacing Parts

Flush the cooling system before replacing any parts like the radiator, thermostat, or water pump. Flushing the coolant system will remove the old contaminated fluid with brand new fluid. Flushing the system can also reveal an obstruction in the system like in the heater core. Removing old contaminated fluid will also allow you to see the contamination for further diagnosis.

3. Use Manufacturer’s Specified Coolant

It’s important to use the manufacturer’s specified coolant. If the coolant says concentrate, add distilled water to the coolant and create a 50/50 mixture of coolant and distilled water before adding coolant to the system. If there is too much water or concentrate, the freezing point might be off. To prevent this, we recommend purchasing a 50/50 mixture of prediluted coolant.

4. Replace the Radiator Cap with the Radiator

Replace the radiator cap when the radiator is replaced. The radiator cap has a spring that activates a valve and lets coolant flow into the overflow tank once there is enough pressure in the cooling system. If the spring is weak, the pressure inside the cooling system will be affected and the coolant will be at a lower temperature than needed.

5. Consider Replacing the Thermostat When Servicing the Cooling System

We recommend replacing the thermostat when servicing the cooling system. It’s usually not a hard repair to do, especially if the coolant has already been drained to replace another part like the radiator.

If the thermostat opens too easily, the vehicle will heat up slower, and if the thermostat is stuck closed, the coolant will be restricted from flowing in the system, causing overheating.

Particles from a radiator sealer built-up in the radiator neck
Particles from a radiator sealer built-up in the radiator neck

We also recommend not using a radiator stop leak kit, since the remaining particles in the coolant that do not plug the leak can contaminate the system and sometimes block and create build-up in other parts. We recommend finding the leak and fixing it as soon as possible.

This article explains how to find a coolant leak.

How to Replace a Radiator Yourself

1A Auto’s how-to videos cover many repairs for many makes and models. If your radiator is displaying symptoms of failure, replace a bad radiator yourself with our step-by-step instructions.

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Common Bad Radiator Symptoms
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Common Bad Radiator Symptoms
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The radiator helps cool the coolant in the cooling system. If the radiator is failing, it can cause engine overheating and coolant leaks. This article covers 5 common bad radiator symptoms, some pro tips for repairing a radiator, and how to replace a radiator yourself.
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