Car Problems Due to Frozen Coolant

by John S. Kepler

Water-cooled engines are compact, efficient and, when well-maintained, can provide years of trouble-free service. They do have absolute limits that cannot be exceeded, however. One of these limits, which is a major problem to people in some parts of the world, is the freezing of the coolant and the problems frozen coolant can cause.

Conditions for Coolant Freezing

Most engine freezing problems are related to water-cooled engines in cars and trucks. Water freezes at 32 degrees F, or 0 Celsius. Unlike most liquids, water expands when it freezes. Since an engine block is not flexible, the expansion can actually crack the cast iron or aluminum block of the engine, ruining the engine. The same principle is at work when water pipes freeze in the winter. This problem was recognized early on which led to the development of anti-freeze. A 1:1 water anti-freeze (ethylene glycol) mix will stave off freezing until -30 degrees F (-35C).

Partial Freezing

If the coolant in an engine degrades over time, or if coolant boils off and is replaced with water letting the mix fall below 1:1, or if temperatures fall below -30 F, the potential for coolant to freeze becomes increasingly likely. This, however, doesn't mean the engine will be destroyed. In many cases, the coolant will turn to slush more than ice. While this won't crack a block, it will mean coolant can't flow. So even though the engine will heat up quickly and melt the slush in the block, the radiator will remain frozen. When this happens, water can't circulate through the radiator and even in low temperatures the engine can overheat and damage can result. In fact, the damage will probably be much more severe than a typical boil over. When an engine runs hot and blows steam out the radiator, you know it is time to turn the engine off. But when the radiator is frozen, there will be no steam and you won't know to shut the engine down until it seizes, by which time it is too late. It is important then, when temperatures are low, to keep an eye on the temperature gauge. If it rises quickly and doesn't stabilize at the normal operating temperature, the engine should be shut down and the radiator checked for freezing. As soon as the radiator thaws, the car should be fine and you can be on your way--though the coolant mix should be checked.

Freeze Plugs

Very low temperatures or diluted anti-freeze will cause the water in the block to freeze solid. This is not good for the engine. When water freezes, the expansion force is in the tens of thousands of pounds. Since the radiator is a reservoir full of water, this expansion can easily rupture the delicate tubes of the heat exchanger. While a radiator is costly to repair, an engine is much more expensive. Fortunately, engine designers anticipated this problem and incorporated a feature into engines that helps avoid expensive damage. When the engine was built, the manufacturer bored large holes from the outside of the block into the water jacket. Soft metal plugs are then pressed into these holes to form a tight seal. These are called "freeze plugs" and will be forced out of the block if the water freezes. These freeze plugs act as a way to relieve the pressure. While the freeze plugs must be replaced by a qualified mechanic, the time and expense is far less than for an engine. When freeze plugs are forced out, though, an engine will still start normally. However, as soon as the water melts, it will all leak out. The danger is that with no water in the engine, there will be no boil over and the temperature sensor--which measures water temperature--will continue to show low or normal temperatures. If the operator is not diligent the first indication of a problem will be engine seizure. If it is cold and you smell a strong sweet odor, turn off the engine and check for leaking fluid. It may ruin your day, but freeze plugs are an easy fix.

From Bad to Worse

In some cases, if the temperature falls enough, or if you have neglected servicing of your car for an extended period, not only will the freeze plugs be forced out, but the block will crack. The cylinder heads might crack. Both could happen at the same time. As before, the engine may start, but this time not only will all the coolant be lost, but most likely, the oil will be lost as well. Low oil pressure soon after starting the engine along with the sweet smell of anti-freeze may indicate a serious problem.

Avoiding the Big Freeze

The best advice is to change the radiator fluid in your car or truck every other autumn. A 1:1 mix of water and anti-freeze has shown to give the best protection against both freezing and boil over. Plus, you will have the added benefit of removing harmful acids that build up in engine coolant over time. If you live in an area where the temperature often falls below the danger zone, you may want to install a block heater, a well-known preventive in these areas.

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