TIPS ON AIR COOLING

- by Bob Hagin
Contributing Editor
The Auto Channel

    When VW put water-cooled heads on its Vanagon bus in the early '80s, 
it brought tears to the eyes of aficionados of the marque. "It's the end 
of the air-cooled engine in this country," a friend lamented to me. 
"Simplicity is dead."
    The last mass-produced American car that utilized direct air cooling 
of the engine was the Franklin of the mid-30s, and while it was a 
Franklin helicopter engine that found its way into the tail of the 
Tucker, it was necessary to install water-cooled heads to make the 
engines last as long as they did.
    But unless you're usual mode of transportation is a power boat, the 
vehicle you're driving is actually air-cooled. The heat just takes a 
slight detour before it returns to the atmosphere. What we're talking 
about here is a system that gets rid of excess engine energy (heat) by 
using a heat transfer device commonly known as a radiator.
    The gist of it is that without a properly operating cooling system, 
the average automotive engine would have a very short life expectancy. 
About 15 to 20 minutes after the cooling system fails, the engine is 
usually ready to be recycled into a newer, gentler vehicle.
    The use of a radiator filled with some sort of coolant to draw off 
excess engine heat has been around just about as long as the automobile 
itself.  Early car makers found that the passage of air over the engine 
cylinders was OK as long as those cylinders were exposed to the passage 
of air as in the case of a power mower. But they also found (the hard 
way some times) that when their engines were placed in a confined area 
(such as under a hood), another means of disposing of the heat was need.
    By the beginning of World War I, there was a liquid-filled radiator 
sitting out in front of most of the world's cars. An exception was the 
gargantuan Renaults - and their radiator was behind the powerplant.
    The principle is simple: the engine cylinders are surrounded by 
enclosed passages filled with a liquid. When the engine is running, 
these cylinders give off heat as a by-product of combustion (an energy 
waste, by the way), that heat is transferred through the metal of the 
cylinders and into the liquid. The liquid then makes its way into a tank 
(usually built into the top of the radiator), flows down through a bunch 
of tubes that connect the top tank to a similar one on the bottom of the 
unit and then returns to the engine. As the car rolls along, cool air 
passes over the hot surface of the tubes and the heat is carried off.
    In truth, things aren't quite that simple. The water temperatures in 
the engine are often higher than the normal boiling point of water and 
in order to keep that water in a liquid state, the entire system has to 
be under as much as 15 additional pounds of pressure. The cap on the top 
of the radiator is built to hold this extra pressure once the engine 
gets hot. If it develops a leak somewhere, the coolant can boil away and 
soon the engine is history.
    Another non-simple factor in this "simple" system is that the 
coolant has to be "pushed" through the system by a mechanically operated 
device known as a water pump. This device also must be sealed against 
coolant leakage and if the drive system (usually but not always a belt 
driven by the engine) fails, big trouble again can happen. One more 
item, the fan that helps draw air through the radiator, has to be 
functioning correctly or there won't be enough air going through the 
radiator to do the job.
    You may have noticed that I switched from saying "water" and now use 
the term "coolant."  All auto and truck builders recommend that the 
cooling systems of their cars use about half water and half antifreeze, 
a combination that raises the boiling point of the solution by about 25 
degrees. Antifreeze is also a corrosion inhibitor.
    But the addition of some antifreezes can cause radiator problems, 
too. Many engines contain aluminum parts and in some cases, the radiator
itself is made of aluminum or plastic. Some commercially available 
antifreezes have had problems when mixed with very hard water and some 
European auto makers have banned the use of these brands in their 
products. But if an antifreeze isn't used at all, corrosion can take 
place and the residue can plug the radiator, the engine cooling passages 
or both. When the cooling passages become plugged, the system has to be 
"power-flushed" with a liquid cleaning agent which is forced through the 
engine in the reverse of the usual flow path).
    Straight water can also cause the radiator tubes themselves to 
corrode from the inside. At this point, either the radiator has to be 
rebuilt (the top and bottom tanks removed and soldered or epoxied to a 
new core of tubes) or a new unit installed. In either case, it isn't 
cheap.
    With periodic checks for hose leaks, proper belt tension and a 
biannual change of the coolant, the radiator and the cooling system will 
last for many years and many miles.