Engine Freeze Ups Cause Overheating

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Winter temperatures provide the perfect environment for vehicles to overheat. Although it seems counter-intuitive cars and trucks overheat when the engine freezes up. This article talks about how this can happen and how to handle it if it does.

Submitted: February 22, 2016

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Submitted: February 22, 2016



There’s snow on the ground, the temperature outside hasn’t reached 32 degrees for days  and your temperature gauge is reading “H”. How can it happen that a car can overheat in the middle of the winter?

First, let’s consider the reason that would cause the most embarrassment, which would only happen to a friend and not to you. The car’s engine has frozen up because of a lack of anti-freeze. Yes, the car overheated because it froze up. No this isn’t double talk, it’s just how a car’s cooling system works. It’s all about flow.

When you haven’t protected your car’s cooling system with a sufficient concentration of anti-freeze/coolant, the water and coolant mixture will freeze. Sometimes this happens in the radiator or in one of the hoses. The frozen mass creates a blockage and prevents the coolant from circulating through the engine to keep it cool. This lack of flow causes the coolant to “sit” in the engine block, and without circulation, the fluid will eventually boil from all the heat the engine is producing. It is, after all, called an Internal Combustion Engine.

To digress, just a bit, motor freeze ups are what make engine blocks crack. Automotive engineers, however, have provided neat, little, ninety cents, metal cups usually about the diameter of a quarter that they call freeze plugs and have placed them in the engine block. The idea is that should the engine block freeze up, the freeze plug will pop out as the ice expands and save the block itself. This is the automotive version of the canary in the coal mine. However, if the freeze is hard enough, the block will crack in spite of the presence of the plugs. A cracked block is a coup de grace to a motor and sends many otherwise useable vehicles to the shredder.

 If this digression serves to point out the importance of checking anti-freeze strength, it was worth writing. All wise-cracking aside, diluted anti-freeze can happen to anyone. A hose replaced on the road during the summer is a likely scenario for “just topping off with water” and then forgetting that the cooling system has been compromised.

The proper way to deal with a frozen engine is to move the vehicle to a warm enclosure and gradually thaw the engine. After some time inside you can run the engine for brief periods while constantly monitoring the temperature gauge, if you’re not able to let it defrost overnight. 

The other reasons a car can run hot in cold weather have nothing to do with the temperature outside, but with mechanical failures unrelated to climate. A thermostat that is not opening or a water pump (a rare occurrence) not pumping or a leak in the cooling system causing the coolant level to become insufficient, all will cause a car to run hot. A radiator clogged with corrosion is no different than one that is frozen and will create the same overheating symptom. However, this is rare in cold weather because of the cooling effect that cold ambient air has on the car as it travels down the road.

Checking the strength of your anti-freeze at the beginning of winter is the best way to avoid a freeze-up. But if your car begins to run hot in cold weather, it’s not a bad idea to think of the worst and make sure you don’t have a frozen engine.

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