A fault in an air-cooled system is not as easy to trace as on the water-cooled layout because the engine is surrounded by ducting. It is advisable that the following areas be checked every 6000miles.
Ensure that the air intake at the fan housing is clear of obstructions. A mis-sharpen air hose may have collapsed inter-nail, if you are suspicious, unclip it and check the inside.
Support the car on ramps and check underneath for any looseness of fixings holding the ducting, or any damage to the ducting.
Lubricate and check the action of any flap valve leakages.