Symptoms That My Radiator is Going Bad

by Keith EvansUpdated July 06, 2023
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The radiator is a primary component of a vehicle’s cooling system. Although radiators are based on a simple design and often last for years with few issues, problems can develop occasionally. As a radiator fails, it may create identifiable symptoms such as puddles of coolant or an overheating engine. If your radiator is going bad, replacing it may be necessary in some cases.


The radiator’s primary purpose is to cool liquid coolant as it circulates through the car's engine. The cooler liquid re-circulates to the engine and keeps the car running cooler. However, if the radiator is going bad, its cooling capacity may be degraded or the radiator could fail completely. For this reason, a faulty radiator typically causes higher operating temperatures in the engine or, in a worst-case scenario, a complete breakdown caused by overheating. According to the automotive website Tegger, a bad radiator can lead to overheating during heavy acceleration, when driving at high speed or when coming to a stop after highway driving. However, these symptoms may also indicate a faulty thermostat or a failing radiator cap. Likewise, a car that overheats immediately after starting may have electrical issues or problems with the temperature sensor unit rather than a failing radiator.

Leaking Coolant

Because the function of the radiator is to disperse heat from the car’s liquid coolant and then return the coolant to the engine, the fluid must flow through the radiator and usually collects in the radiator reservoir. If the radiator fails or if it becomes cracked, the coolant may begin to leak out. Such leaks are not always easy to detect, as coolant may drip onto pavement while you are driving or onto a parking lot where you might never notice it. Moreover, coolant leaks can develop at any point in the vehicle’s cooling system. F

or this reason, coolant pooled on a driveway or garage floor does not necessarily indicate a bad or cracked radiator. To identify the origin of a coolant leak, the AA 1 Car website recommends having a professional mechanic perform a pressure test. During this test, the mechanic adds a colored dye to the vehicle’s coolant and then uses a machine to pressurize the cooling system. As the dyed coolant leaks out, it leaves a temporary stain that can help identify or rule out a bad radiator.

Radiator Sludge

Automotive coolant is a liquid, usually colored green or yellow, and its consistency generally is that of water. If a radiator goes bad, rust or debris may contaminate the fluid, leaving it rust- or oil-colored. A rusty radiator may also cause flaking in the coolant, which eventually creates a sludge that no longer efficiently cools the engine. My Honest Mechanic warns that radiator sludge will not completely drain, and sludge that remains in a radiator after a coolant flush will continue to inhibit cooling; for this reason, drivers should replace a radiator that develops sludge.

Video showing symptoms of a bad radiator:

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