Allowing an engine to reach its optimal temperature quickly, yet preventing it from overheating, is of vital importance for its proper functioning--this is precisely the job of a radiator valve. When an engine is first started, the valve is closed, thereby preventing the radiator fluid from entering the engine. This allows the engine to quickly warm. Once the engine reaches optimal temperature, the valve opens and allows radiator fluid to enter the engine. It is for these reasons that a defective radiator valve is a common cause for engine overheating or for prolonged warm-up times.
Remove the radiator cap, then lower the radiator's antifreeze level. Radiators are equipped with either a drain bolt or a petcock plug, each of which is located at the base of the radiator, usually on the side of the radiator facing the engine. A petcock plug looks like a wing nut. If the radiator uses a drain bolt, remove the bolt with a wrench and allow the radiator to drain until the fluid level falls below the top radiator hose, then reinstall the bolt. If equipped with a petcock plug, loosen the plug by turning it in a counter-clockwise direction with a wrench, until radiator fluid exits from the centre of the plug. Tighten the plug once the fluid level falls below the top radiator hose.
Follow the top radiator hose from the radiator to the spot where the hose attaches to the engine. Note that the hose attaches to a metal elbow on the engine. That elbow is the radiator valve's housing and, as its name suggests, contains the radiator valve.
Slacken the clamp which holds the top radiator hose to the valve housing. The design of hose clamps varies, but clamps typically feature a single screw on them. Loosen the screw with a screwdriver until the clamp loosens, then pull the top radiator hose off the housing.
Remove the radiator valve's housing from the engine. The vast majority of housings are attached to the engine with two bolts, although some use three. Remove each bolt with a wrench, then pull the housing off the engine to expose the radiator valve.
Pull the radiator valve out of the engine.
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