Ode to the Air-Cooled Engine

No new cars, and just a dwindling handful of new motorcycles, have engines that rely on the air to cool them.

Technically, it’s airflow which washes over the exterior surfaces of the engine (in some cases, is forced to wash over the exterior surfaces by an engine-driven fan—that’s you, old Beetle, old Corvair and also not-so-old Porsche) and that, along with oil, cools the engine.

Both transfer heat.

But no water is involved, which means no radiator and no water pump buried deep in the guts of the engine—or hoses or thermostats and (best of all) no road trip-ending leaks.


No one ever needs to replace any of those many and often expensive parts, which the air (and airflow plus oil) cooled engine hasn’t got.

It also means easier access without all the extra parts to get at the engine.

Well, sometimes.

Air-cooled motorcycle engines are easy to get at. They usually hang in the breeze, literally.

The necessity of this airflow means not covering the engine with covers. The air-cooled motorcycle engine is generally just there.

Accessible and visible.

You can lay hands on almost all of it without tools and without having to remove a bunch of peripheral parts first.

This has the additional benefit of looking good—the industrial art of fins and castings, alloys and chrome plating. An air-cooled engine is a work of art that works.

Sometimes, the beauty is hidden beneath tinwork and shrouds as in the old Beetle and other old air-cooled cars like the Chevy Corvair and, of course, classic (and even fairly recent) Porsches.

This is both for cooling and heat.

This time, to conserve it and use it.

Remember: No radiator means no warm coolant to warm up the car’s interior, so no warmth (for the car’s occupants) when it’s cold outside.

Thus, in an air-cooled car, the necessity (absent an accessory gas heater or some other apparatus) for not letting all of the engine’s heat just waft away into the air (as it does on an air-cooled bike, which doesn’t matter because there is no interior to warm up).

Instead, air heated by the engine is captured and redirected to the car’s cabin, cozying up the joint.

The idea not only kills two birds with one stone (cools the engine by taking it away from the engine; warms the car’s interior by directing the engined-warmed air into the passenger compartment) it is also faster.

Water-cooled engines take longer to warm up because they have thicker blocks and cylinder heads (to accommodate water jackets/cooling passages) and because it takes a while for engine heat to build and transfer to the liquid medium (the coolant) and eventually (it often seems like an eternity on really cold days) provide warmth for the passengers.

Air-cooled engines warm up much faster.

Their castings tend to be thinner and there’s no need to heat up a medium (the liquid, in air-cooled engine) to transfer the heat of combustion to the passenger compartment. If you’ve had the good luck to drive an air-cooled car in winter you know the heat works almost as soon as you turn the key.

Well, assuming the tinwork is tight and the fan is working correctly. Air-cooled (and heated) Beetles have a rep for being drafty but it’s really the result of being old and not in good repair. No one denounces air-cooled Porsches for coldness, which is usually because Porsches are better cared-for than old Beetles.

The concept remains sound, is the point. Arguably, sounder than the water-cooled concept, if the object is to reduce complexity, ease serviceability as well as get warm quickly when it’s very cold out.

German cars were air-cooled for a reason. It gets cold in Germany.

So, what happened to the air-cooled concept? If it’s such a sound concept, how come it’s almost extinct in terms of what’s available new . . . except for lawn mowers and weed whackers, that is?

The former provides the clue that gives us the answer.

Lawn mowers and weed whackers aren’t yet subject to the degree of emissions regulations that cars and motorcycles have.

Porsche was the last car company to offer an air-cooled car for sale, back in 1998.

Rather, Porsche was the last car company to be allowed to sell one.

The rest, including VW’s air-cooled cars, had been forced off the market one by one by emissions regs that got progressively stricter to the point that complying with them became too expensive and too much hassle.

Even Porsche, with all its engineering know-how and (unlike VW) far less constrained by cost and the need to keep it cheap, eventually had to knuckle under to Uncle.

This happened more than 20 years ago when the last of the air-cooled 911s left the factory. Since then, all Porsches, all cars sold in the United States, period have been water-cooled.

But why is it so hard to comply with the regs using the air-cooled layout?

The first reason is that air-cooled engines tend to run hotter than water-cooled engines and this creates emissions issues; or rather, different compliance issues.

Not major, but different.

Compliance requires sameness. One size fits all. The rules, you know.

The second and related reason is that it’s more of a challenge to regulate the operating temperature of an air-cooled engine than a water-cooled engine, which makes it harder to precisely control its emissions under all operating conditions.

There is a temperature sweet spot that engineers striving to comply with emissions regs seek; that sweet spot is easier to hit with water-cooling.

It’s not that air-cooled engines are “dirty.”

The problem is purely one of pedantry. The air-cooled 911 isn’t compliant, which is a very different thing than being dirty.

The distinction is analogous to the charge of “dirtiness” leveled at VW’s diesels (water-cooled, for the record) which weren’t by any sane standard anything other than “non-compliant” — i.e., they didn’t quite comport with the regulatory minutiae in every Inspector Javert-esque detail, no matter how pedantic or immaterial to air quality. This is like the equivalent of being issued a ticket for “speeding” 3 miles-per-hour faster than the arbitrarily posted limit.

Guilty, perhaps but criminal? Only to an Inspector Javert.

It was enough to demonize them and to eliminate them.

The precedent for that set decades prior, when low-cost air-cooled cars such as the Beetle were regulated off the market.

Air-cooled bike engines are probably next.

Your push mower, too.

Just wait.



Photo attribution: Michael Barera licensed under the Creative Commons Attribution-Share Alike 4.0 International license.

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One Response to “Ode to the Air-Cooled Engine”

  1. Dave Coe says:

    I suspect that electric mowers will replace the air cooled gas mower.
    My friend has one, seems to work OK.