5 Signs of a Bad or Clogged Radiator (And Replacement Cost)

(Updated on June 9, 2022)

Radiators are critical for maintaining cool, efficient engines. If you have a bad or clogged radiator, your vehicle is very likely to overheat.

An overheating vehicle usually won’t make it very far down the road before it quits working completely. This turns a fairly cheap repair into a very expensive one.

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What Does a Car Radiator Do?

Back in the day, cars used to be air cooled. Now that engines have become bigger and more complex, almost all engines are water cooled. The term “water” is often used interchangeably with coolant, radiator fluid, and antifreeze in conversation.

How It Works

Water cooling is achieved by pumping coolant through little passages in the engine block. Hot coolant from the block then makes its way back to the radiator through a circuit of hoses.

Air passes through the radiator from front to back, while coolant passes through the radiator from side to side. As the air moves through the radiator fins, it pulls the heat out of the radiator. This also transfers heat out of the coolant.

Once the thermostat opens, this cool water enters the engine block. The temperature inside the block drops to a predetermined value, then the thermostat closes again. The process continues until you turn off your car.

Where is the Radiator Located?

Most radiators are located in front of the engine. As you drive forward, air passes through the grille and into the radiator.

Your vehicle is also equipped with one or more radiator fans. These fans blow cool air over the radiators if your vehicle is stopped. If you’re stuck in traffic or sitting in line at a drive-through, your radiator fans should kick on automatically.

Symptoms of a Clogged or Bad Radiator

1) Overheating

engine overheating symptoms

Overheating is the easiest way to tell you have a radiator problem.

If your car has overheated, there are several components you want to check. Once the engine cools down, make sure you have enough coolant in the cooling system.

You may also want to check to see if your head gaskets and intake manifold gasket are still good. In rare cases, you could have a cracked cylinder head or block from repeated overheating.

2) Coolant Leaks

coolant leaking

A bad radiator usually leaks. If you notice coolant leaking out of the front of your engine, it may be time to replace your radiator.

Sometimes a leak will only present itself when the cooling system is under pressure. You can check for leaks using a radiator pressure tester kit. These kits are available from $50-100, but you can likely rent one for free at your local auto parts store.

Check to make sure you don’t have a leaking coolant hose. These are much cheaper to replace than the entire radiator. You can find many hoses for a few dollars at your local auto parts store.

Related: Losing Coolant But No Visible Leaks? (Here’s Why)

3) Low Coolant Warning Light

low coolant warning

Newer vehicles may alert you when your coolant level drops. If you notice a low coolant light but the car has not overheated, you should still pull over to check the coolant level when it is safe to so do.

Driving with low coolant is likely to damage the engine.

4) Sludge Buildup

coolant sludge

Coolant is often a fluorescent green color, but it could be blue or orange as well. If your coolant looks dark brown or black, it’s probably time to change the coolant.

If you drain your coolant and notice chunks or a thick, viscous mess, you may have a clog in your radiator. Radiator clogs may develop from coolant that is very old, the presence of engine oil, or excessive Stop Leak.

5) Water Pump Failure

bad water pump

Did you know that a bad radiator can also cause your water pump to fail? Water pumps are lubricated by the passage of coolant. If there is air in your cooling system, you may not be getting a constant supply of coolant to your water pump.

Water pumps often weep coolant or make some bearing noise before they fail entirely. If you notice either of these symptoms, it may be a good time to inspect your entire cooling system.

Sometimes water pumps also fail because of an incorrect timing belt adjustment. In this case, you may need to readjust the timing belt or chain tensioner so that there is less stress on the water pump pulley.

What Causes Radiator Failure?

corroded radiator

Although the radiator core is made out of metal, the end tanks are often made out of plastic. Plastic deteriorates over time.

Old plastic radiators have been known to burst and spill coolant everywhere. Fortunately, you can often prevent this from happening. If the plastic around your radiator is starting to look brown, it may be a good time to proactively replace the radiator.

Since much of the radiator is made of metal, the radiator may also be susceptible to corrosion, both inside and outside. If you live near the coast or an area that salts the roads, check your radiator for rust. Corrosion inside the radiator is mitigated by changing the coolant regularly.

Does a Malfunctioning Radiator Make Noise?

Radiators themselves should not make any noise. If you hear a hissing sound accompanied with some steam, you probably have a pinhole leak in your cooling system.

There are plenty of times when a bad radiator will make no noise at all. Don’t rely on sound alone to tell if you have a clogged radiator.

Can You Drive With a Bad Radiator?

While it’s technically possible to drive with a bad radiator, it is highly recommended that you don’t, unless absolutely necessary. A bad radiator may quickly lead to overheating.

Once your engine overheats, there is a very good chance you will warp a head or blow a head gasket, leading to a much more expensive repair.

How Long Do Car Radiators Last?

how long do radiators last?

Radiators are typically designed to last the life of a vehicle. This could be well in excess of 100,000 miles, or 8-10 years. Each vehicle is different, and radiator build quality may vary.

Sometimes radiators are subjected to debris or impacts that damage the fins in the core. Bent fins may prevent proper cooling of the engine. Although the process is quite tedious, you can sometimes bend back radiator fins yourself.

Radiator Replacement Cost

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radiator replacement cost

Most radiators are fairly straightforward to replace and are easily accessible.

Radiators typically cost between $200 and $1,000 to replace at a shop. This will depend on the quality of the parts, the location of the radiator, and the shop’s labor rate. If you opt to replace the radiator yourself, expect to pay between $50-300 for the radiator itself. Don’t forget to factor in the cost of new coolant, which should run between $20 and $50.

This is a repair many people can tackle on their own. Most radiators are held in with a few bolts. Drain the coolant, unplug the radiator fan(s), disconnect the upper and lower radiator hoses, and the radiator should lift right out of the vehicle.

If you have an automatic transmission, you may have to remove a few additional lines at the bottom of the radiator. Automatic transmission fluid is often cooled by the main radiator.

If you do this job yourself, make sure you have a pan handy to catch any fluid that drains out. You will have to top off the cooling system, then bleed the system of air. If you lost any transmission fluid from the radiator replacement, top off the automatic transmission fluid as well.

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