If air-cooling proves sufficient for much of the running time (such as for an aero-engine in flight, or a motorcycle in motion), then oil cooling is an ideal way to cope with those times when extra cooling is needed (such as an aero-engine taxiing before take-off, or a motorcycle in a city traffic jam). But if the engine is a racing engine that is always producing huge amounts of heat, water or liquid cooling may be preferable. Air-cooled aviation engines may be subject to “shock cooling” when descending from cruising altitude prior to landing. During descent, very little power is needed, so the engine is throttled back and thereby develops much less heat than when maintaining altitude. While descending, the plane’s airspeed rises, substantially increasing the rate of air-cooling the engine. These factors may cause the cylinder head to crack; but the adoption of oil-cooled cylinder heads significantly reduces or cancels the problem as the heads are now “oil-warmed”
