Every year, engine heaters are put into service, only to find out that the first trouble some, cold day, they're not operational. This expensive lesson can be avoided with simple inspections during routine maintenance.

The most common cause of failure of engine heaters is improper coolant mix. Today's engine coolant is a complex mixture of chemicals and additives designed to increase the efficiency of the cooling system, when properly combined. A cooling mixture that exceeds the ratio of 60 percent chemical to 40 percent water will not transfer heat produced by the heating element fast enough, causing element to overheat, prematurely burnout. A weak mixture lower than 50 percent chemical to 50 percent water will allow the coolant to boil around the heating element. This will cause cavitation, or minerals in the water to bake onto the element sheath, treating and insulation equal to that of the strong mixture.

Electrical engine heaters should be checked for continuity and signs of coolant leakage.

A continuity checked of the heaters should be made with an ohm meter. With the power cord connected to the heater, take a reading across the two power terminals. The meter should show a very low resistance, typically a 1500 watt element will read between 9 -- 10 ohms. If there is no reading the element has failed. If the reading is very high, the element is close to failure.

A continuity checked should also be madebetween the either the power terminals and the ground terminal. The ohm meter should have no reading; if it does, the heater should be replaced. Also check with the meter connected between the ground terminal of the power cord and a good vehicle ground. The meter should jump to a zero reading. If it does not replace the cord.

To check for coolant leeks on emersion style heaters, remove the power cord from the heater body. The power cord should be inspected for serviceability and replaced if necessary. Look at the heater electrical terminals. They should be cleaned and free of corrosion. There should be no signs of coolant leakage between the element and the heater body or around the mounting gasket surface. For externally mounted heaters, all hose connection should be checked for signs of leakage, and all hoses should be inspected for serviceability.

Replacement intervals for electrical engine heaters will vary upon usage patterns in cooling system conditions. These devices should generally be replaced when the engine is overheated.