6 Symptoms of a Clogged or Bad Radiator (and Replacement Cost)

As an engine runs, it produces heat. The purpose of the radiator is to cool the engine and prevent it from overheating. A car’s engine uses coolant to absorb the heat and transfers it to the radiator where it cools down. Once it cools, the coolant is sent back into the engine and the process starts over again.

When your radiator is clogged, not working as efficiently as intended, or has simply gone bad, not enough cooling is taking place inside the engine. This can result in your car overheating and if not fixed soon enough, permanent damage to the internals of your engine.

A radiator can be clogged from the inside, outside, or simply fail altogether. Here are some signs of a clogged radiator you’ll want to look for before expensive engine damage occurs.

Common Symptoms of a Bad or Clogged Radiator

#1 – High Temperature Gauge Readings

high temperature gauge

Since a functional radiator prevents the engine from overheating, you will know something is wrong with the radiator if the engine starts overheating. Monitor the temperature gauge to see if the readings are higher than usual or if the needle is in the “red” zone. Some newer cars will display the temperature digitally and warn you when the engine temperature gets too high.

A normal operating temperature for most cars is somewhere between 195 and 220 degrees F. If the temperature falls slightly out of that range, it’s often not a cause for alarm, especially in summer months when the air conditioner is constantly running.

But if the temperature consistently stays on the hot side, it’s possible you have a clogged radiator. This usually occurs from corrosion due to rust, internal deposit buildup over time, or debris getting stuck in the radiator which prevent the proper amount of coolant from circulating through the radiator and your engine.

#2 – Coolant Leaks

coolant leak

The housing or cooling fins may develop tiny holes or cracks on them when the radiator is clogged due to severe rust buildup. Once this happens, you may be able to see small drops of coolant on your garage floor or driveway.

The rust inside your radiator often forms due to a low quality coolant or adding regular tap water (instead of distilled) to the coolant mix which has many more contaminants. If a radiator flush is not regularly done, more and more rust will form and start eating away at the radiator tank.

With even the slightest coolant leak, your vehicle will be forced to operate with an insufficient amount of coolant and the low coolant level light may illuminate in your dash. If you don’t fix the leak as soon as possible (or at the very least keep the coolant level topped off), your engine may overheat and even need expensive repairs due to internal damage.

#3 – Fluid Discoloration


Vehicle coolant should be a bright green or yellow color (or sometimes red or pink) and flow freely through the radiator and coolant passages within the engine. Over time, internal deposits and even sludge can contaminate the coolant. This will turn it into more of a rusty color or even the color of oil. Checking the coolant overflow tank is often the easiest way of checking the condition of the coolant.

This contaminated fluid will also be slightly thicker and not allow it to easily flow through the cooling system. This in turn starts to clog up the radiator and if you let it get bad enough, the radiator’s efficiency may reduced to the point of causing your car to overheat. A radiator flush should be performed asap.

In addition, 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.

#4 – Exterior Radiator Fins Blocked

dirty radiator

Radiators are designed for maximum cooling. To accomplish that, thin fin tubes run across the front of the radiator. These tubes carry hot coolant. As you drive, the radiator fan pushes outside air on and around these fins to lower the temperature of the coolant before it flows back into the engine.

If these tubes become clogged up by dirt, bugs, leaves, or other material, the airflow is blocked which doesn’t allow the coolant to cool as much as it needs to. On most cars, there is usually enough access (you may need to remove a plastic cover or two) to use a garden hose and spray nozzle to wash off any debris that may be blocking the front of the radiator.

#5 – Bent or Damaged Fins on the Radiator

bent radiator fins

In addition to clogging due to foreign material stuck to the front of the radiator, airflow can also be blocked when enough fins get bent or damaged. These fins are extremely delicate and a piece of tiny gravel hitting them while driving can cause damage. 

Damage can also occur during installation of a new radiator or even when spraying water to clean off the fins. If too much water pressure is used such as when using a concentrated stream or pressure washer, the fins can easily bend and block the flow of air. When enough fins are damaged, it can clog the radiator enough to cause engine overheating.

#6 – Heater for Passenger Area Not Working

heater not working

The cabin heater of a car depends on hot coolant passing through the heater core and then the resulting hot air being blown into the passenger area by a blower fan. If the radiator is clogged or has a leak, not enough hot coolant makes its way to the heater core to allow proper warming of the car’s interior.

A bad thermostat is most often the issue but sometimes, an issue with the radiator can be the culprit.

Average Radiator Replacement Cost

radiator replacement cost

The cost to replace a radiator is one of those things that can vary quite a bit. Overall, you can expect to pay somewhere along the lines of $200 to $900 total to replace a radiator with most vehicles falling in the $400-$500 range.

A typical radiator with aluminum core and plastic tanks can run anywhere from $100 to $600 depending on vehicle make and model and whether it’s OEM or aftermarket. Something like a Ford Focus radiator is going to be on the lower end while something like a Chevy truck with a large Duramax engine (with built in oil cooler) or luxury car will be on the upper end.

The amount of time it takes to replace a radiator also varies. For some cars with easy access, it can be a 1-hour job while some tighter, more complicated set ups (ie: Audi or Porsche) can take closer to 3 hours. Expect to pay somewhere in the vicinity of $100 to $300 for labor.

In addition, other parts may also be necessary as part of the job. New coolant is usually needed and sometimes hoses, hose clamps, radiator cap, and the thermostat are also replaced at the same time. Factor in an additional $15 to $100 in miscellaneous parts.



  1. My car is not running hot is no leaks we just replace the radiator but when I take the cap off I noticed the antifreeze is not circulating in the radiator and I am concerned about that but like I said there’s no leaks it’s not overheating it’s not running hot so what is the problem

    • Bad thermostat or water pump are the two common causes of coolant not circulating in the radiator although the car would overheat after a while. How long did you allow it to run?

  2. VERY HELPFUL INFORMATION! Definitely evidence of a small leak, however it is not leaking to the ground! A temperature gauge only ran hot once but my car does not blow heat consistently in the winter time does not blow cold air consistently in the summer! I have a mechanic check it he put coolant in the car and the air is working fine! There is still concern that there is a leak somewhere, but they want to charge me over $1000 to replace the radiator,

  3. Had same problem definitely water pump. If you keep running it there will be more pressure in your water bottle and take cap off while driving

  4. Have a 2001 Nissan pathfinder. Its get hot when I drive a long distance about 25 miles. But around town its stay normal. Replace the Fan Clucth(that’s what a repair shop told was the Issue) the shop told that wasn’t the problem! Now their telling me I have a Clogged Radiator! 467$ to replace the Radiator! I’m going to flush the Radiator. What could the problem be? Need help Plz!

  5. I have a 1999 Mitsubishi Galant it has been getting hot. I filled the overflow reservoir a week and a half ago and yesterday it got hot again when the ac was on. I turned the ac off and it went back to normal. When I got home and the car cooled down I looked and the reservoir was half empty. After I drove to work which was about a 30min drive I noticed the car smelled like coolant and a little when I went back outside there was a puddle under my car. Im not sure what to check any advice?

    • Common points of leaks are the radiator cap, reservoir tank, and the upper and lower radiator hoses so you want to check those first. But there are of course other areas (radiator, heater core, thermostat housing). A pressure test can also be done by a mechanic to find the leak.

  6. I have a 2004 dodge Durango 4.7 I changed thermostat and water pump and aux water pump my heads are not cracked checked them new raidtor cap my truck is still running hot the top hose is hot the bottom hose to thermostat is cool what is causing my thermostat not to open and flow all answers are very helpful

  7. Very educative. In cars that do not have a temperature meter except for a glowing red light how does one monitor the terperature status. I have a Honda City 2011 model.

    • Thanks Joaquim. Since it doesn’t have a temp gauge, the easiest way would be to hook up a diagnostic scan tool that displays real-time data including the engine coolant temperature.
      I’m a big fan of the BlueDriver but there are many other scanners that will read the temperature.

  8. I have a Lincoln navigator that has a radiator that is filled with dirt and oil caked on the whole outside and in the fins. What could be the reason?

    • The outside of the radiator can get dirty just from normal driving (bugs, dirt, etc.) or if you have an oil leak somewhere. It’s recommended to clean the radiator about once a year (or when the fins start clogging. After it’s allowed to cool, spray on some Simple Green or other degreaser on the front of the radiator and let it sit for a few minutes. Then, use low pressure water on the BACKSIDE of the radiator to rinse it off. The fins on the front are super delicate and prone to bending so never scrub the front (unless very gently with soft bristles) or spray water on the front.

  9. My car is running hot and I have replace the thermostat and water pump but my engine is reving super high as it is crunk what could it be

  10. I have a 06 grand prix, replaced thermostat, water pump and tensioner elbows. Radiator replaced less than a year ago. Car still overheats, only thing thats unusual radiator cap is hard to get of even when engine is cold.

  11. Hi my ford Everest 2013 model i’ve flushed the radiator several times and after two or three weeks theres oil inside the expantion tank and the engine will start to overheat and the engine oil is still ok without any water in it,my ver worrying concern is why is there oil in the water,please help..

    • Unfortunately, you likely have a blown head gasket (not a cheap fix). A local mechanic would easily be able to confirm.

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