Problems with the radiator can present in several ways, and diagnosing them is not always as simple as checking for coolant leaks. We’ll go through the main symptoms of a bad radiator and what you can do to repair the problem.
Engine overheating is the most common symptom of a bad radiator. Other signs include a sweet smell coming from the engine, temp gauge rising, dirty/discolored coolant, coolant leaks and check engine lights.
But before you go and replace the radiator, check the whole coolant system as it shares symptoms with other parts.
What is a Radiator?
Before we move on to telling you how you can diagnose a bad radiator, we’ll explain exactly what a radiator is and what it does.
The car radiator is one aspect of the cooling system that keeps your vehicle’s engine operating at ideal temperatures.
This heat-exchanger is located in the front of the car and contains two linked water tanks connected by many narrow tubes. Hot coolant comes from the engine and is pumped through one of the tanks into the core.
As the car moves, colder air is forced between all the narrow tubes. This action draws the heat from the coolant. The cooled fluid then pumps out of the radiator and back into the engine.
The Role of The Radiator
Something every novice car owner knows is when 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, that is 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, that is using a gaseous fluid instead of the liquid coolant.
Common Signs Of A Bad Radiator
The most common symptoms of a bad or clogged radiator include engine overheating and unusually high temperature readings on the gauge.
You might also notice coolant leaks, damaged radiator fins, heater problems, or consistently low coolant levels that require frequent topping up.
Here’s a closer look at the most common signs of a bad radiator you should watch for.
#1. Overheating Engine.
The engine tends to overheat once the radiator gets bad enough. If there’s a clog, then the radiator can’t provide the cooling power needed to disperse the heat.
You may see steam or smoke coming from under the hood when it overheats. The temperature gauge will also be pegged in the danger zone.
There are many other issues that can lead to an overheating engine, so more diagnosis is needed.
For example, a defective water pump or thermostat failure can also lead to an overheating engine. Either way, as soon as you notice your car overheating, it’s important to stop driving immediately.
#2. High Temperature Readings.
If you are accustomed to driving your vehicle, you’ve likely learned where the temperature gauge normally reads.
When it starts to read slightly higher than normal, it means that the coolant is getting too hot. If you are extremely attentive, you will notice even the slightest variations in temperature, which gives you the warning you need that something is wrong.
With a blockage preventing airflow, the fluid can’t cool down, so the engine temperature reads higher than usual. If you allow it to continue, the engine will eventually overheat and you could damage the motor.
#3. Coolant Leak.
When the fluid in the radiator isn’t able to flow properly, a leak can occur from the excessive amount of pressure. You may notice the leak at the radiator or in one of the hoses where the pressure built up.
Either way, the lack of fluid can quickly cause the engine to overheat, especially if the system doesn’t have enough fluid inside. That’s why all coolant leaks should be dealt with promptly.
#4. Damaged Radiator Fins.
The radiator fins are made from metal that can become damaged. Because of where the fins sit, they are susceptible to debris, such as rocks kicked up from the road. This problem occurs even more frequently if you travel off-road or drive down a dirt driveway.
If the fins get damaged, the airflow may suffer. In exchange, the coolant can’t remain at a normal temperature, so the engine starts to overheat.
#5. Heater Malfunction.
You may not think that the cooling and heating systems have anything to do with the radiator, but that’s not true.
The heater in the car’s cabin relies on the hot coolant passing through the heater core to produce warm air. This warm air is then blown into the cabin with the help of the blower fan.
When the radiator gets clogged or if there’s a leak, the hot coolant may not be able to get to the heater core. Therefore, you may notice an inability to get warm air out of the vents.
#6. Low Coolant Level.
If there’s a leak, the coolant level may drop too low. Without the right amount of coolant, the engine is sure to overheat.
Additionally, the fluid can start to look contaminated. Coolant that’s flowing freely through the engine should be bright in color, whether it’s green, orange, pink, yellow or blue. If the system is contaminated with sludge, the coolant starts to appear rusty or oily instead.
This contaminated fluid can also become thicker than it should be. This thicker fluid has trouble flowing through the radiator, causing the same overheating issues.
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 which 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.
How to Diagnose a Bad Radiator?
Checking the Cooling System
With so many components working together, you can’t just go right to the radiator, unless you already know it’s the problem. At the dealerships, we like to work through a series of checks to find the failed parts.
#1. Failed thermostat.
You will need an infrared temperature gun. Then, follow these simple steps:
- Warm up your car engine. Give it ample time.
- Look for the radiator hoses. There is an upper and lower radiator hose on your car.
- Scan the radiator hose temperatures with the infrared gun. Wait for your engine to overheat and measure both hoses.
- If both hoses stay cold, or just one becomes hot, then you have a bad thermostat. Don’t be a macho man and attempt to measure this by touching the hoses. Obviously, they can get very hot and you could burn your hand.
#2. Clogged radiator.
If your radiator has an internal clog, the coolant flow is restricted. If you have an external clog, it might cause the airflow to become restricted and lead to overheating. Here’s what you need to do to check:
- Your engine must be cool. Leave it parked and off until it’s not warm at all.
- Look inside the radiator. You need to remove the cap and inspect for debris. If you have an internal clog, you’ll need to replace the radiator.
- Look for external clogs. Examine the front of your radiator for debris that could have clogged it. You should be able to clean an external clog with a garden hose or compressed air.
#3. Cooling system leak.
If there’s a leak in the cooling system, your engine will overheat. You must repair this immediately if you want to prevent further damage. To perform this check, you’ll need a cooling system pressure tester and coolant dye kit.
- Cool the engine completely.
- Take off the pressure cap and set it somewhere safe.
- Follow the manufacturer’s instructions and apply pressure with your tester. Don’t exceed what’s written on your radiator cap.
- Examine the system for a leak.
- If you need to, add some coolant dye after removing your tester.
- Put your radiator cap back on and start your engine.
- Watch for a leak by keeping an eye open for the dye. Sometimes, it takes days of regular driving until you see the dye—this indicates a slow leak.
#4. Defective cooling system pressure cap.
Can a bad radiator cap cause overheating? Yes. If your cap isn’t holding pressure, the coolant starts to boil and leads to an overheating engine. Keep your system pressure tester handy for this check as well.
- Cool the engine completely.
- Unscrew the pressure cap and remove it.
- Use your pressure tester on the cap. Make sure it holds the recommended amount, as per the cap. If not, replace it.
#5. Malfunctioning water pump.
When a water pump breaks, it doesn’t circulate the right amount of coolant. This also leads to an overheating engine. You don’t want to check this until you’ve done the thermostat inspection first.
- Cool the engine completely.
- Take off the pressure cap.
- Start the engine and watch the coolant to see if it begins circulating.
- If it doesn’t move, you could need a water pump.
- Look at the water pump. It might have signs of a leak. Look for wet spots or dry green or white residue.
#6. Faulty radiator cooling fan.
When the cooling fan fails, your engine overheats.
- Park the car.
- Look for the cooling fan. It might be mechanical or electric, but the engine drives it.
- Start the car and let the engine warm up.
- When the engine temperature rises higher than normal, inspect the cooling fan. If it doesn’t turn on or seems to be running slow, this might be your problem. For a mechanical fan, you must replace the clutch. With an electric fan, you want to diagnose the circuit first.
#7. Defective head gasket.
The issue no one wants to have is an internal problem with the engine, but it happens often. The way to prevent this is to repair cooling system defects immediately. That means, don’t put water in your radiator and ignore the leaks.
To perform this check, you’ll need a block test kit.
- Cool the engine.
- Remove the radiator cap.
- Hook up your block tester. Make sure you follow manufacturer specs.
- Watch for an indication of combustion gases in your cooling system. If it shows evidence of gases, you have to disassemble the engine for further troubleshooting.
As you can see, finding out if you have a bad radiator is more complicated than just looking at the part. That’s because the cooling system contains multiple components, and when one aspect isn’t running right, it leads to the same symptoms.
You can’t automatically tell that a thermostat or radiator is the culprit just because the engine overheats.
How to Fix a Bad Radiator?
Diagnosing a bad radiator is all about looking at the most likely symptoms and the most probable failures. Radiators most often fail by rusting, which causes either leaks or contamination of the coolant liquid.
So, if you’ve got a low coolant level, visible leaks under the radiator, or if the coolant is discolored and has deposits in it, the radiator is a likely cause.
#1. Flushing the Radiator.
The radiator can accumulate gunk and particles inside it over the years, and sometimes a simple flush and clean is all it needs. We’ve covered all kinds of radiator flush methods: with vinegar or baking soda or with a garden hose (redneck style).
You can find all the information you’ll need in these articles, but here’s the gist of it. You’d disconnect the upper and the lower radiator hose, stick a garden hose in the top, and let the water run. As it runs, it’ll come out the bottom, and flush all the nasty stuff out with it.
Keep in mind that unless you’re dealing with an extreme case, this procedure won’t be necessary for cars that are 5-10 years old, only older vehicles.
#2. Plugging Up a Leak.
Radiator tends to either clog up or start leaking. The best way to solve a radiator leak is to have it welded or replaced, but there are also other, creative ways to do it.
I would not recommend using those anti-leak balls. While they are effective at stopping leaks, they are just as effective at making clogs in the system and will often clog up the cabin heater core.
Powdery solutions are less risky but I wouldn’t use one of those either. Adding ground paprika or an egg yoke to the system are well-known DIY methods, though I would only recommend it for better cars.
How to Flush And Replace the Radiator?
Swapping out the radiator is a time-consuming job, but not difficult and you can save a lot of money by doing the work yourself.
Mechanics will charge for every hour of labor so the cost can easily go into hundreds of dollars. Alternatively, with a few basic tools, you can do the job yourself in the garage or even the parking lot.
The reason why I’m talking about flushing again is that you really need to do it before installing a brand-new radiator.
A good flush is going to clean the system and prevent immediate clogging of the new radiator. There are several methods to do a flush, but I’ll explain the most effective.
Besides these these tools, you will need a lot of distilled water, which is cheap and easy to come by.
You’ll also need some containers to catch the spilled coolant. You can use any radiator flush fluid, but get the appropriate coolant for your vehicle. New upper and lower radiator hoses are optional but given how cheap they are you might as well replace them.
#1. Prep for the Radiator Flush.
The most important thing to remember when working with the coolant system is to work on it while it’s cold!
Read the instructions on the coolant flush fluid and use it accordingly. Some mix with water while others work with coolant – whichever the case, add it to the reservoir and drive for some time to get it circulating through the system.
Now we can let all the coolant out into a container by unscrewing the bolt at the bottom of the radiator and then opening the radiator cap.
You’ll notice just how dirty and discolored the coolant appears compared to the new one. If the coolant doesn’t leave the reservoir, trace the lower reservoir hose, disconnect it, and drain the rest of the coolant.
The reservoir needs to be scrubbed or pressure-washed to get all the built-up deposits off. You can spray inside with a garden hose or use a brush that’ll fit inside to clean it. Once you’re done, just reconnect the hose back to close the circuit.
It’s a good idea to swap the thermostat while you’re at it, just so you have the peace of mind that all the components are good.
But as we’re still doing the flushing, just take the thermostat out and reconnect the hoses. The reason why we do this is because we don’t want the thermostat obstructing the flow of water as we begin flushing.
#2. Flush the Radiator.
Now it’s time to flush the radiator – place the funnel on the radiator cap and fill it up with distilled water.
You can add another radiator cleaner if you want to make the flush more effective, but it’s optional. You’ll need to start the car at some point to get the water circulating so that more can fit in. Seal the radiator and fill the reservoir.
Turn on the car, crank up the heat, and monitor the coolant gauge for temperature spikes. After a couple of minutes, you can go for a short drive or just let the engine idle for 10 minutes.
When you start the next cycle, just make sure not to burn yourself on the heated water. The next steps repeat the cycle of prep and flush – drain the fluid, clear the system, reconnect everything, pour water, and start the engine.
You’ll do this until the water coming out at the drain is noticeably clear. It doesn’t have to be perfect, but the more flushes you do, the better the results.
Once you’re done, install a new thermostat but don’t fill the vehicle up with coolant, we’ll do that after swapping the radiator.
#3. Swap the Radiator.
- Disconnect the negative cable of the battery.
- If needed, remove the components getting in the way of swapping the radiator, like the intake hose.
- With the pliers, disconnect the clamps holding the lower and upper radiator hose in place.
- Removing the hoses can be difficult so try twisting as you pull.
- If there are transmission lines leading to the radiator, carefully unscrew them with the flare nut wrench.
- Loosen the bolts holding the fan shroud in place and the fan will disconnect from the radiator.
- Unscrew the radiator bolts and you can pull the radiator up.
- Replace the upper and lower radiator hoses. They’re usually held in place by a clamp that should come right off.
- Before installing the new radiator, make sure to transfer all the extra parts from the old one.
- To install the radiator, lower it in place, then work in the reverse, tightening and attaching hoses.
- Fill up with coolant and top up transmission fluid if needed.
How much does it cost to fix a bad radiator?
On average, you may spend $200 to $1,000 to have the radiator professionally replaced. If you can do the job yourself, you won’t need to spend as much.
However, the price could go up even more if you want to replace other parts at the same time, such as a radiator cap or thermostat.
FAQs.
Q: Can you drive with a bad radiator?
You shouldn’t drive with a radiator that’s not functioning correctly. If the coolant retains heat as it re-enters the engine, it won’t be able to dissipate the high temperatures from the motor. In a short time, the engine can overheat, which often leads to permanent damage.
Q: Does a bad radiator affect the AC?
A clogged or bad radiator can affect an AC system if there isn’t enough airflow. You may notice increased temperatures in the cabin when the radiator is clogged. It can become difficult to cool the cabin in severe cases.
Q: Does a bad radiator affect the heater?
Yes, you may notice that the cabin doesn’t warm up well enough when the radiator is clogged.
The heating system relies on the same coolant, passing through the heater core, to warm the cabin. If the coolant can’t get to the heater core because of a clog, you will have trouble getting comfortable in winter.
Q: What is the average lifespan of a radiator?
If the radiator and cooling system are maintained, it could last for the lifetime of the vehicle. However, in most cases, the radiator only lasts for eight to ten years.
If you drive in an area with salty air, the radiator could fail prematurely. The salt air leads to corrosion, which takes its toll on radiators.
Last words
Bad radiator symptoms ignored could mean spending extra time and money. A faulty radiator causes an engine to overheat.
This could be as a result of coolant leaking, damaged fins, bad radiator cap or head gasket, etc. Not Paying close attention to these signs could cause engine breakdown or permanent damage.
Thus, spending unnecessarily, funds you could have diverted to other important things. So it is ideal that you check for bad radiator signs and fix them.
Replace faulty radiator when necessary to avoid engine damage. If you can’t handle it, calling an expert mechanic will be a good option.