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Radiator Leak

System Affected Cooling System
Severity High. Can lead to engine overheating and failure.
Symptoms Coolant leak
Engine overheating
Rising temperature gauge

A leaking radiator can lead to serious engine damage by preventing the engine from being cooled. The loss of coolant through a leak will make it difficult for the remaining coolant to dissipate engine heat.

Table of Contents


Coolant Leak

The most obvious symptom of a radiator leak is the appearance of coolant under the vehicle. Coolant can be green, orange, or bright pink. It should smell a little sweet and feel like greasy water. Since your cooling system is pressurized so it can keep a certain level of heat in, it will constantly be searching for the weakest link in the system to relieve pressure, when functioning properly this should be the radiator cap, but when there is a leak, the cap gets bypassed.

Depending on where the leak has formed, coolant may or may not appear on the ground. For example, a leak in the bottom of the radiator will likely result in a puddle. On the other hand, a leak near the top of the radiator may only allow coolant to escape while the engine is running. Sometimes you can see coolant in the fins of the radiator if it has evaporated due to a hot engine or radiator. This is still a leak even if it is not pooling

Places to look: Water Pump, Radiator Hoses, Heater Core Hoses, Radiator.

Coolant Loss

With a small leak in the radiator, there may not be enough coolant leaking to for a puddle. Over time, the coolant resevoir level will drop, triggering a "Low Coolant" light on some vehicles, or a slowly raising temperature gauge.

Coolant Does Not Return from Reservoir

Almost all vehicles utilize a coolant overflow reservoir or recovery tank and a pressure cap to maintain proper coolant levels while under pressure. A leak in the radiator can alter the flow from the reservoir to the radiator. The coolant would expand and be pushed out of the radiator as the pressure rises, however the leak prevents a sufficient vacuum from forming to draw the coolant back to the radiator.

Sometimes if the resevoir has recently been topped off at a service appointment this may give the illusion that coolant cannot return to the cooling system.

Engine Overheating

One of the primary causes of an engine overheating is a lack of coolant. If an engine continually runs hot, there may be a leak in the cooling system.

Heater Blows Cold Air

Since coolant flowing through the heater core warms the air, a significant loss of coolant would result in a reduction of heated air.

Inspection of the cooling system may be required, if no leaks are found, than a malfunctioning thermostat, or internally leaking head gasket could be the cause of a lack of heat.

Temperature Gauge Rises Steadily

A perpetual rise in the temperature gauge signifies an inability for the engine to remove its heat. A reduction in coolant levels through a leak would make coolant cycle through the engine faster, preventing it from removing all of its heat before returning to the engine.

See also: Thermostat stuck closed, Radiator Fan Malfunction, Leaking Water Pump,



There are two different causes of corrosion in the radiator core that result in leaks. One is external corrosion, this comes from the radiator being on the forefront of the vehicle, it is mounted in front just behind the grille, this means it gets pelted with everything on the road, including salt, and gravel, and water and bugs, pretty much whatever is out there, over time the radiator (even though it is aluminum will rust) will corrode and rot through creating a leak.

Radiators can also corrode through the inside. Coolant is acidic, and slowly becomes more and more acidic over time from the chemicals constantly being battered by the rapid and extreme temperature changes inside the engine. If the coolant isn't changed on a semi regular basis it can prematurely corrode radiators, gaskets, o-rings and anything else in the system to create leaks. Regular services and flushes of the cooling system are typically recommended at around 90,000 miles to prevent damage to the cooling system.

Transmission Cooler Internal Leak

On some vehicles with automatic transmissions, the Automatic Transmission Fluid (ATF) is sent to a small radiator sometimes separate from the engine's radiator and sometimes part of the same assembly. This ATF cooler is meant to cool the oil for the transmission and keep it from over heating, then sends the cool oil right back into the transmission to be reused. On conjoined radiator systems the oil and coolant are kept separate inside the assembly, but if internal corrosion occurs (typically on higher mileage vehicles) than coolant and ATF will start mixing and can cause severe damage to both the systems if not addressed immediately. This includes damage to the engine because ATF does not flow as well or cool as well as coolant. Symptoms include a creamy strawberry milkshake like substance in the radiator and coolant resevoir, engine overheating, transmission slipping, swollen rubber cooling hoses and gaskets from the ATF.

This article was last edited on March 19th, 2011 at 6:43 PM
Category: Cooling