Cooling system

The petrol engine is only about 25% efficient. That is to say of all the potential energy in the fuel only a quarter is used to propel the car. Three gallons out of every four are wasted in heating up the engine. In fact so much heat is produced that the engine would become red hot and long before this happened it would seize up and cease to function.

Some parts of the internal combustion engine would melt from the heat of the burning gas if no cooling system were provided. However it would probably be more correct to refer to the engine cooling system as a " temperature regulation" system. We do not want the engine to run too hot neither do we want it to run too cool. We would like to maintain the water jacket temperature slightly under the boiling point of water or at about 200 deg.F.

There are two types of engines: water cooled and air cooled.

The cylinder walls of air cooled engines operate at a tem­perature considerably above 200 deg.F. in many cases. This is hot to touch, but cool in comparison with the heat generated in the combustion chamber of the engine.

As the fuel is burned in the combustion chamber, about one third of the heat energy of the fuel is converted into power.

Another third goes out the exhaust pipe unused, and remai­ning third must be handled by the cooling system.

It is interesting to note that the heat removed by the coo­ling system of a large motor truck at normal speed is sufficient to keep a thirty-five-room house warm in freezing weather. Even a passenger car engine will develop enough heat to keep a six-room house warm in zero weather.

This means that several gallons of cooling water must be circulated in the cooling system every hour to absorb the heat and carry it to the radiator. It also means that many thousands cubic feet of air must flow through the radiator every hour in order to dissipate the heat to the air. It is important to distinguish between heat transfer and heat dissipation.

The heat generated by the mixture burned in the cylinder must be transferred from the iron cylinder to the water in the water jacket.

The outside of the water jacket dissipates some of the heat to the air surrounding it, but most of the heat is carried by the cooling water on to the radiator from when it is dissipated to the air.

Thus the heat flows or transfers from the cylinder iron to the cooling water, and from the cooling water to the copper radiator.

Iron water and copper are all good conductors of heat, sо if they are in good contact, the heat will flow readily from one to another. If, however, there is a coating of lime or rust between the water and the bare metal the flow will be re­tarded because lime and mat are very poor heat conductors.