Section 16.6

Induction, Exhaust & Cooling

Induction and alternate air, exhaust and the CO hazard, and air/liquid cooling with cowl flaps.

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Main ideas

The induction system draws air through a filter and intake manifold to the cylinders; an alternate-air/carb-heat source bypasses the filter (drawing warm, unfiltered air) to clear icing or a blocked filter.
The exhaust system collects and routes the burnt gas overboard through manifolds/stacks and silencers; a shroud around part of the exhaust provides cabin and carburettor heat via a heat exchanger.
A cracked exhaust or muffler is a carbon-monoxide hazard: CO can enter the cabin through the heat shroud — CO is colourless, odourless and dangerous, so exhaust integrity is a flight-safety item.
Most light aircraft are AIR-COOLED: finned cylinders with baffles and cowl flaps direct the cooling airflow; cowl flaps are opened for climb (low speed, high power) and closed in the cruise/descent.
Liquid-cooled engines circulate coolant through cylinder jackets to a radiator; cylinder head temperature (CHT) must be kept in limits, and rapid power reductions can cause damaging 'shock cooling'.
⚠ Exam trap: cabin/carb heat is drawn from a shroud around the EXHAUST — a cracked exhaust/muffler can admit carbon monoxide to the cabin; cowl flaps regulate cooling airflow and are opened for high-power/low-speed climb.

Solved examples

Why should cowl flaps be opened during a full-power climb but closed in the cruise?
In the climb the engine is at high power (lots of heat) but low airspeed (little cooling airflow), so the cowl flaps are opened to admit maximum air over the cylinders and keep CHT in limits. In the cruise the airflow is plentiful and heat lower, so closing the flaps reduces cooling drag and prevents over-cooling.

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