I'm not sure where Chris' message comes from, I can't see the original,\nso I'm guessing the context.\n\nAir cooled cars don't just cool the engine when they are travelling at\n100kmh. Some air-cooled engines used a fan to blow extra air over the\ncooling fins, but many did not. Normal air flow is sufficient to keep\nthem in a safe operating temperature, the hot engine warms the air, which\nflows away and is replaced by cooler air.\n\nIt's possible to design CPUs to work the same way. My wife is using a PC\nright now with a 1.66GHz Atom CPU and no CPU fan. Even though the power\nsupply fan died, the machine is still running perfectly, with two laptop\nHDDs, and no overheating. 1.66GHz is plenty fast enough for web browsing,\nword processing, email, etc.\n\nGo back 30 years, and I don't think that the average PC needed a CPU fan.\nPossibly not even a case fan. Just the normal air flow over a small heat\nsink was enough. And of course, your mobile phone has no room for a heat\nsink, unless it's tiny, and no fan. And people expect it to keep working\neven when shoved in their pocket.\n\n[QUOTE]\nIf the car were *always* moving at 100km/h, it probably wouldn't need a\nfan.\n\nIn practice, all cars do have fans (even the ones that aren't\nair-cooled), for the occasions when they're not moving that fast.[/QUOTE]\n\nThat may be true of water-cooled engines *now*, but it's not a law of\nengineering. Many air-cooled engines do not (did not) require a fan, or\nonly needed the extra cooling when stuck idling for long periods in hot\nweather. E.g. Beetles didn't use a fan. (A great idea for Germany, not so\nmuch for hot and dusty Southern California, as my wife can tell you.)\n\n[QUOTE]\n(BTW, so-called water-cooled engines are really air-cooled too, just not\nby air flowing directly over the engine block. (Although marine engines\nmay be an exception.))[/QUOTE]\n\nYes, technically water-cooled engines are cooled by air too. The engine\nheats a coolant (despite the name, usually not water these days) which\nthen heats the air.