Vintage Car Life Tech: “Air Cooling For Cars?” – There Was One Benefit That I’d Not Considered Before

In addition to road tests, Car Life also had a regular tech column, written by Roger Huntington, who really knew of what he said and wrote. This article, from March 1964, takes a close look at air cooling, its pros and cons, and dispelling some myths.

At time this was written, the Corvair obviously blew new life into air cooling—as well as rear engines. History shows that to have essentially been a lot of hot air; air cooling was soon seen as a dead end, most importantly because the inevitable high combustion chamber and cylinder temperatures had a very negative effect on NOx. one of the smog-forming emissions that was in for serious regulation.

But those same high temperatures also had a real benefit, one that I hadn’t thought of. Hint: Did you ever notice that VWs and Corvairs never seemed to blow blue smoke, something that was not uncommon with other engines back then?

Air cooling has a long history, and in the US, the Franklin was the main exponent, all the way through 1934, even with a 12 cylinder engine. In Europe, air cooled engines were very common, for obvious reasons. The smaller the engine, the greater the relative cost of water cooling. That explains your air cooled lawnmower, among other things.

Average gas temperatures of some 1200° F obviously need to be kept in check. Heat transfer via a liquid coolant is very efficient; “the heat transfer coefficient between the cylinder wall and the water in a jacket is roughly 100 times greater than between the same wall and a blast of air flowing over it.” This is of course the reasons for fins and blowers in an air cooled engine.

Nevertheless, interior cylinder walls and combustion chambers will run significantly higher in an air-cooled engine than a liquid-cooled one. “On a liquid-cooled engine, these surfaces are only about 50-75º F above the temperature of the water in the jacket…On a typical air-cooled engine these surfaces will run generally between 400 and 550° at full power—or roughly twice that of the water-cooled engine.” Air simply can’t transfer the heat efficiently enough.

The result is that these high surface combustion temperatures invite pre-ignition and detonation. This explains why air-cooled engines generally had lower compression ratios, including high-performance ones like the Porsche 356/911, until such time that electronic knock sensors were implemented.

Another concern about air cooling was the power consumed by the fan. It is of course somewhat higher than the power consumed by a water pump, and it peaked with maximum rpm and power, but in ordinary cruise conditions, it was not significant, less than 2 hp, in the case of the Corvair, since it had thermostatic controls to limit the fan’s demand.

The radiator’s impact on air flow (aerodynamics) is negative, compared to an air cooled car. The Corvair was the most aerodynamic American car at the time.

Noise from a blower can be intrusive, but can also be largely mitigated. And of course the air cooled engine itself makes more noises, as it lacks the water jackets, effective sound barriers.

A common assumption is that air cooled engines are more expensive to build; tell VW that! There’s a reason they kept it in production for so long: it was cheap to build. No radiator, water pump and all of the related hoses, etc.. Yes, some larger air cooled engines might have been a bit more expensive than a comparable water cooled one, but the difference, if there was one, was not significant. Since most air-cooled cars had rear engines or FWD, there was also no drive shaft and related parts required.

Now to the advantages: Obviously the lack of a liquid cooling system, which tended to be more troublesome back then than nowadays, like so many things. The lighter weight is of course perhaps the biggest benefit, which made rear engine cars less tail heavy than if they had water cooling. The Corvair engine weighed some 100 lbs less than the Falcon six, despite it being exceptionally light due to its advanced thin-wall castings.

Now we get to the benefit I hinted at: air-cooled engines seem to last longer! It hasn’t just been my imagination, and helps explain why the VW engine (and the Corvair) had reputations for simply lasting longer, especially in term of ring and cylinder wall wear, which of course caused oil consumption (blue smoke) as well as reduced compression and such. I cannot remember a VW engine wearing out its rings and cylinders; if it died, it was from a dropped valve, or broken crank, or burnt valves, or something else. I ran two VWs with original engines well over 100k miles, and both were still in excellent condition. Meanwhile, British engines used to require a ring job seemingly every 50-60 k miles. Why was this?

“Most ring and cylinder bore wear happens when the engine is running cold. Lubrication is marginal at this time, clearances are tight, there is much scuffing and much of the wear is due to the corrosion from condensed acids.” But the air cooled engine warms up much faster, and the hotter cylinder walls burn off the acids quickly. My anecdotal experiences are finally verified.

Of course all of this is essentially irrelevant in modern engines.

Then of course there’s the heating bugaboo, with air-cooled engines. “There’s plenty of warm air available from the engine, but the problem is to duct it efficiently to the passengers with sufficient force and without engine odors“. The 1960 Corvair depended on a gasoline-fired heater, but for 1961, the Corvair had a well-developed engine air-heated system with a heat exchanger and a fan. According to Huntington, “Volkswagen engineers have never developed a decent heating system in all the years the car has been built“. Ouch! I beg to differ, but then he probably didn’t know you have to crack open the vent window. And make sure that the system has not been compromised.

Huntington goes on to muse about possible advances to air cooling that might tilt the scales more towards that approach, but in reality, that’s just tilting against windmills cooling blowers. Air cooling was of course a dead end, although not yet for a while. The last two new cars with air cooling were the Honda 1300 (1969) and the Citroen GS (1970). We have a great post on those two here. Of course Porsche kept blowing hot air all the way to 1998, with the 911 993.


Related CC reading:

Automotive History: The Last Two New Air-Cooled Car Engines

Why Millions Of People Think Old VWs Had Terrible Heating – Operator Error

Automotive History: Corvair Warm Comfort – Heating Optional (1960-1961); Your Choice of Gasoline or Engine Heat