Causes for a car leaking antifreeze under the hood

Written by richard rowe
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Causes for a car leaking antifreeze under the hood
Leaking antifreeze can be a serious problem. (Getty Creative)

Oil and antifreeze are life's blood for your engine, but an antifreeze leak can have several consequences that an oil leak may not. Steaming antifreeze can easily work its way into any one of your car's electronic components, ruining sensors, electric motors and actuators alike. Additionally, the ethylene glycol used in many antifreezes is extremely dangerous to animals; this substance may taste like sugar water, but ingesting it will lead to delirium, paranoia, hallucinations and ultimately death.

Open caps

This seems obvious, but you might be surprised how many people are driving around with an open radiator or coolant tank reservoir cap. A loose radiator cap may feel tight at first, but most are double-locking. Push down on the cap hard, give it a clockwise twist and engage the locking tab to make sure.

Normal overflow

A certain amount of heat-induced coolant expansion is normal. As the coolant heats up, its water component turns to high-pressure steam. That steam causes fluid to bubble and expand, pushing it out of the radiator overflow tube and into a (usually) plastic catch tank. If your system has a little too much water or starts running a little too hot, the catch tank will spew water out of its vented cap and into the engine bay.

Leaking hose

Radiator hose leaks are among the most common reasons for coolant in the engine bay and can have a number of causes. Heat softens the rubber over time, turning what would have been a harmless abrasion into a full-on cut quickly. Hose clamps also can work their way through the soft rubber, and splits may occur where the hoses clamp onto their mounting nipples.

Radiator holes

A fine spray pattern on the front of your engine may indicate a pinhole leak in your radiator. The steam in your radiator will squirt water out of even the tiniest of holes, and the cooling fan will turn that stream into a misty spray. Coolant leaks typically occur where the radiator crossover tubes are brazed onto the tanks or the fins are brazed onto the tubes.

Leaking gaskets

A leaking water pump gasket or thermostat housing gasket will cause an external coolant leak, but they are easily repaired. A leaking intake manifold gasket or, far worse, a blown head gasket, also will cause external coolant leaks. These two may or may not be accompanied by water in your engine oil. A blown head gasket may be accompanied by the smell of fuel and bubbles in the radiator, a dense white or blue exhaust cloud and constant steaming around the exhaust manifold.

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