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
I did have a VW engine give out due to worn rings/cylinders, a type 4 engine in a 77 Bus. I don’t know the whole history of the engine of course, and it may have had several valve jobs while not touching the pistons, but it gave out with low compression on the highway. It was run, for quite a while I’d guess, with no thermostat and missing air ducting gaskets. Runs great now with a new p&c kit
I think an interesting aspect of the cabin heating issue that was entirely overlooked involves the fact that the air-cooled engines discussed in the article were installed in the back of the car. I don’t have personal experience with front-engine air-cooled cars, but I’ve seen fewer complaints about cabin heat in cars like the Citroen 2CV and GSA than I have in VW or Corvair.
There is one other advantage of air-cooled that I remember from long ago–an air-cooled engine isn’t prone to overheating even in hot environments. Witness the WWII North African campaign where Rommel’s Afrika Corps used VW-derived command cars and carriers (I doubt the Panzer tanks were air cooled, but I don’t fully know) whereas the Allied forces had their water-cooled Jeeps and other small mobile troop vehicles. Loss of water/anti-freeze and radiator disabled vehicles and the need for additional parts (that was covered in this article, don’t forget thermostats) and also just because it’s functioning doesn’t mean a water-cooled engine won’t over heat (I remember in 1970 in Miami when my grandfather was picking us up at the airport and we got stuck on the expressway–he had us roll down the windows of his AMC Hornet and he turned on the heater at full blast. He answered my question why and he said we needed to blow the excess heat off). Air-cooled had a simplicity of design and maintenance, an advantage in resource scarce places.
I’m no expert but I think most of the Allies’ tanks used in North Africa were air cooled radials. IDK about the Axis.
German tanks were typically powered by Maybach v12 watercooled spark ignition engines. Mitsubishi made an aircooled diesel v12 tank engine which did see service. Sounds interesting.
The U.S. Army experimented with Chenowith Fast Attack Vehicles (sand rails) in the mid 80’s. As recon vehicles, they were excellent, because their air cooled engines cooled down to air temperature much faster than a jeep’s liquid cooled engine. Thus we could go into hide positions and the thermal imaging systems at the time couldn’t pick up the infrared “heat” signature of our FAVs after a short 15 minute cool down. The infrared imaging systems could pick up a jeep’s engine heat signature for up to an hour and a half after shutting down due to the liquid cooling system.
Pistons and cylinders might last a long time in an air cooled VW engine, but the exhaust valves and cylinder heads certainly don’t. After 60,000 to 70,000 miles a VW cylinder head customarily needs either a valve job or to be replaced because an exhaust valve has broken off or the valve seat has dropped and destroyed the head in question.
3rd cylinder. Because the oil cooler was in the airstream. So the oil was used as an added liquid cooling system. Ignition of the 3rd cylinder was retarded by 3 degrees because of that situation.
The reason you didn’t see many Corvairs or VW’s blowing blue smoke is due to the high combustion temps that turned the oil into carbon deposits before they hit the exhaust system.
I don’t think so. Never seen an issue with significant carbon build up in them.
Anyway, the actual combustion temperatures are essentially the same.
Always enjoyed Roger’s tech articles. I also enjoyed Gordon Jennings work when he was the tech editor for Cycle magazine back in the 1970s to mid 80s
My 900cc air cooled Ducati Monster motorcycle actually does suffer from slow warmup, due to being fitted with a fairly large oil cooler (standard equipment). When I was using the bike for a daily, 10 mile each way commute even in summer in California, let alone winter, the oil temp never got hot enough to ‘boil off” condensation in the oil. The bike uses a sight glass rather than dipstick, and after a few years I noticed milky sludge in the sight glass when I hadn’t had the opportunity to go for longer rides. This despite regular oil changes, use of synthetic oil etc. I finally learned that a 80-100 mile ride through our local canyons or up the Pacific Coast was needed to keep it clean. Life is tough.
By the way, in the performance bike world, liquid cooling finally sealed the coffin on air cooled bikes due to higher performance enabled by higher compression ratios, larger bores due to closer cylinder spacing, etc almost 40 years ago. Noweven low end bikes have moved away from air cooling due not only to stricter emission standards, but also noise regulations. And many bikes that don’t (yet) use conventional liquid cooling are really air-oil cooled with oil cooling passages that have nothing to do with lube oil distribution, and large capacity oil sumps or tanks and oil-coolers. My single cylinder Suzuki DR650 uses this design, and interestingly I never see white sludge in its oil-level sight glass.
The current overhaul of the engine in my ’69 type 1 VW is almost to 180,000 miles with no head problems or oil burning as far as I can tell. Primary oil loss in this engine seems to be via the pushrod tubes. The original tubes got so holey they were replaced with those tubes that can be installed without taking the engine apart; they do leak some but not like the worn-out originals did.
Type 1 and Type 3 engines (and Type 2s with upright engines) had the oil cooler sitting on top of the #3 cylinder. If you changed the oil and adjusted the valves every 3K miles, which I think was the interval in the owners manual, there was no problem getting >100K out of an engine. Type 4’s and US market Type 2s moved the oil cooler to the back of the engine, copying the Corvair. No more dropped #3 valves! Corvairs had hydraulic valves from the start so no adjustment was required.
Regarding oil consumption, as I recall Volkswagen used at least one cast iron piston ring instead of steel. Maybe that was because cast iron could handle higher temps than steel rings at the time? IDK but I too don’t remember ever seeing either an aircooled VW or a Corvair blowing blue smoke. None of mine ever burned oil.
Corvair engines could be pretty long-lived if those damned leaky pushrod tubes were replaced regularly, which didn’t require taking the heads off. VW too moved to heads-on replaceable pushrod tube O-rings on Type 4s and Type 4 engined buses.
Another good article .
In August of 1963 VW completely changed their heater systems to use fresh air run over finned exhaust pipes ~ this increased the heat of the air at the same time it increased the volume of flow and eliminated the oily engine stink from using waste cooling air previously .
The NSU Prinze, Citroen 2CV, VW and Porsche engines were all designed as economy vehicles so the low power wasn’t much of a thing .
Those who maintained the cooling systems and kept all those fiddly little sheet metal bits didn’t have any reliability issues not short engine life ~ 150,000 miles was normal for a properly maintained VW Beetle .
The Typ IV engine in the 1972 > VW Typ II was a new design, similar to the late Porsche 356C engines .
The Vans typically could get three top ends before needing any bottom end service .
The Typ IV piston pictured shows damage .
Emissions finally put paid to the VW’s, as Paul mentions the NOx emissions were bad and not visible so the average owner didn’t understand but that’s why VW went to the BOSCH Jetronic fuel injection for the 1968 and subsequent models .
I’m resurrecting a 1959 Beetle that’s seen better days, I installed a correct 1,192 C.C. 36HP engine and Sunday last I had no troubles passing almost every other vehicle in the Angeles Crest Highway with two full size adults in the car .
Many non U.S.A. certified Motocycles still use small displacement, low compression engines to very good effect .
Corvairs were darn good cars ~ I owned a 1961 700 Coupe with Powerglide and it was no slouch .
I run nearly stock VW’s and never have any power problems ~ typically I can keep up with all normal vehicles and am nt terribly far behind the Hot Rods .
Those who claim air cooled VW’s are crap don’t maintain or operate them correctly .
-Nate
Deutz still makes a variety of air cooled diesels. I don’t think they’re used in trucks anymore, but at one time they were a popular engine choice in the German-made Margirus trucks. An “L” for The 3rd character of a Deutz diesel designates air (for Luft) cooling.
As was mentioned, the VW heaters were pathetic due to design and the fact that many of them had rusted shrouds and the heater ducts that ran along the running boards were also rust magnets.
The defroster system was worse than the heater.
They were seriously dangerous in that a leaky gasket, not rare, would expose the occupants to unknown dose of carbon monoxide, and the first symptom of that is when you drive into the ditch.
The optional gasoline heater, on the other hand, would melt your boots.
Today’s liquid cooled engines get to operation temperature much faster. one of the reasons is the use of reverse flow liquid cooling. traditionally the coolant runs from the block to the head and through the upper hose to the radiator. In the reverse system it goes, well, in the reverse direction. The coolant hits the hottest part first. And that should help the service life of all engine parts.
I loved my VW bugs back in the 70’s. But they were on borrowed time even then. I mean they were a design from the ’30s, granted updated some, but not much. They were built to be inexpensive and fairly reliable, but things got complicated here in the US where people, including myself, wanted to go 70-75 all day long.
Modern metallurgy, especially on exhaust valves, along with an improved cooling system could have extended their life, but really, it was a dead end especially with emissions. I’m not saying you had to get to Porches level tech to further the platform, but significant upgrades were needed. They probably could have been limped along to about the turn of the century, but would have suffered. They had their day in the sun, performed long after they should have been obsolete in a practical sense, but emissions and expectations doomed them.
Overheating. It’s said they didn’t overheat. On the contrary, they did. They were run long and hard well outside of the design parameters, but they didn’t suffer obvious faults such as boiling over. Just because they didn’t boil over didn’t mean they didn’t have a significantly shortened lifespan due to excessive heat. Re the exhaust valves everyone knows about, let along engine seals that started to leak, and pistons and cylinders that occasionally would either start to seize, or show severe scuffing if taken apart after #3 valve head came off.
I address this mostly towards VWs as that’s what most of the aircooled cars in this country were. They had their strengths and weaknesses, but mostly time just overtook them.
Good points! But they’re still cute as a bug. I’d love to own a beautiful condition 1957-1971 Bug.
Re: opening a vent window for better heat – Even with my water cooled 4 cylinder truck I noticed when driving with the heater temperature on high but the fan off, and in fresh air (not recirculate) mode, a very small amount of heat can be detected from the dashboard vents. If I open the window a bit, especially at faster speeds I definitely notice more warm air flow.
When and if the interior is properly sealed this is a real thing .
It was 35* F today so I decided to take my old VW for a drive, it has no headliner but very little draft through the trunk so I find the heater is fine, I’m in shirt sleeves .
-Nate