In an engine, by reducing the difference in temperature between the combustion gas and the engine metal, you cut the loss (waste) of heat from the combustion gas, so more energy stays in the combustion gas, which is doing the work of pushing the piston. Smokey Yunick wrote in his highly-respected book : “Some guys go to great lengths to keep the engine temperature down … though the engine doesn’t overheat, they don’t realize that they’re putting energy (heat) into the cooling system that could be used to produce power at the crankshaft. Running the engine at 180 degrees will drop the overall horsepower by 2%-3%. For max power the cooling temp should be at least 200 degrees.”
Reducing is a major goal in aircraft design, including the design of cooling systems. An early technique was to take advantage of an aircraft's abundant airflow to replace the honeycomb core (many surfaces, with a high ratio of surface to volume) by a surface mounted radiator. This uses a single surface blended into the fuselage or wing skin, with the coolant flowing through pipes at the back of this surface. Such designs were seen mostly on aircraft.
On vintage cars you may find a bellows type thermostat, which has a corrugated bellows containing a volatile liquid such as alcohol or acetone. These types of thermostats do not work well at cooling system pressures above about 7 psi. Modern motor vehicles typically run at around 15 psi, which precludes the use of the bellows type thermostat. On direct air-cooled engines this is not a concern for the bellows thermostat that controls a flap valve in the air passages.
The secret behind K-Seal’s ability to repair a coolant leak is down to its contents: a specially developed blend of chemical ingredients including ceramic microfibres and copper particles. When added to the cooling system the ingredients disperse and flow freely around the system suspended in the coolant. If coolant is leaking from the system, either externally (look for a puddle under the engine) or internally across the head to the cylinders, then K-Seal will follow it through the hole or crack and try to fix the leak.
Westfalia / Vanagon 2.1L (1986/91) cooling system flow / chart