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Intake Air Preheat System

The intake air preheat system operates a regulator flap in the lower part of the air filter housing. In cold weather the regulator flap opens so that the engine can draw in preheated air from around the warm exhaust system. The system is shown in Fig. 7-8 below. Vacuum from the throttle valve which opens or closes the regulator flap is controlled by the temperature regulator valve in the side of the upper air filter housing.

Fig. 7-8. Intake air preheat system fitted to air filter housing. Cutaway shows temperature regulator valve inside housing.

Test the temperature regulator valve by applying vacuum to the upper port. When the engine is cold, the valve should be open and air should easily pass through. When the engine compartment is warm, the valve should be closed. A faulty temperature regulator valve can be replaced separately.

To check the regulator flap, remove the vacuum hose from the lower port on the temperature regulator valve. Separate the upper part of the air filter housing from the lower part and remove the air filter so the regulator flap is visible. Apply vacuum to the disconnected vacuum hose and check that the flap moves smoothly. If the regulator flap mechanism is faulty, the lower air filter housing should be replaced.

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