to operate properly. A stuck thermostat can either cause engine overheating or overcooling.

If a thermostat is stuck closed, coolant will not circulate through the radiator. As a result, overheating could make the coolant boil.

When a thermostat is stuck open, too much coolant may circulate through the radiator and the engine may not reach proper operating temperature. The engine may run poorly for extended periods in cold weather. Engine efficiency (power, fuel mileage, and driveability) will be reduced.

The procedure for thermostat replacement is as follows:

To remove the thermostat, drain the coolant and remove the upper radiator hose from the engine.

Remove the retaining cap screws holding the thermostat housing to the engine. Tap the housing free with a rubber hammer. Lift off the housing and thermostat.

Scrape all of the old gasket material off the thermostat housing and sealing surface of the engine. Make sure that the housing is not warped. Place it on a flat surface and check the gaps between the housing and the surface. If warped, file the surface flat. This action will prevent coolant leakage.

Make sure the temperature rating is correct. Then place the thermostat into the engine. Normally, the pointed end on the thermostat should face the radiator hose. The pellet chamber should face the inside of the engine.

Position the new gasket with approved sealer. Start the cap screws by hand. Then torque them to the manufacturer's specifications in an alternating pattern DO NOT overtighten the housing bolts or warpage and or breakage may result. Most housings are made of soft aluminum or "pot metal."

Hoses

Old radiator hoses and heater hoses are frequent causes of cooling system problems. Hoses should be checked periodically for leakage and general condition. The leakage may often be corrected by tightening or replacing hose clamps. After a few years of use, hoses deteriorate. They may become soft and mushy, or hard and brittle. Deteriorated hoses should be replaced to preclude future troubles. Cooling system pressure can rupture the hoses and result in coolant loss.

Inspect the radiator and heater hoses for cracks, bulges, cuts, or any other sign of deterioration. Squeeze the hoses to check whether they are hardened or softened and faulty. Flex or bend heater hoses and watch for signs of surface cracks. If any problem is detected, the affected hose should be replaced. However, where spiral spring stiffeners are used to control the tendency to collapse, such test will not work and the hose must be removed for inspection.

Fan and Belt

One of the easiest and quickest checks to the cooling system is the fan and fan belt. Check the fan for bent blades, cracks, and other problems. A bent or distorted fan on one with a loose blade should be replaced. Where the fan is just loose on its mounting, tightening is in order.

Fan belts, or drive belts, should be checked for wear and tension. Most wear occurs on the underside of the belt. To check a V-belt, twist the belt with your fingers. Check for small cracks, grease, glazing, and tears or splits. Small cracks will enlarge as the belt is flexed. Grease rots the rubber and makes the side slick so that the belt slips easily. A high-pitched squeal results from slippage. Large tears or splits in a belt allow it to be tossed from the pulley. On vehicles with a set of two belts, replace both if one is worn and requires replacement.

Use a belt tension gauge to check and adjust the fan belt tension. When you do not have a gauge or if space does not allow use of a gauge, you can make a quick check of belt tension. Press down on the free span of the belt, a point midway between the alternator or generator pulley and the fan pulley. Measure the amount of deflection. When free span is less than 12 inches between pulleys, belt deflection should be 1/8 to 1/4 inch. When free span is longer than 12 inches, belt deflection should be 1/4 to 1/2 inch.

A slipping belt can cause overheating and a run- down battery. These troubles result because a slipping belt cannot drive the water pump and alternator fast enough for normal operation. Sometimes a belt will slip and make noise even after it is adjusted to the proper tension. Several types of belt dressing are available which can be applied to both sides of the belt to prevent this problem. Belt dressing helps to eliminate noise and increase belt friction.