The Cooling SystemWritten by Kevin Schappell
The purpose of engine's cooling system is to remove excess heat from engine, to keep engine operating at its most efficient temperature, and to get engine up to correct temperature as soon as possible after starting. Ideally, cooling system keeps engine running at its most efficient temperature no matter what operating conditions are. As fuel is burned in engine, about one-third of energy in fuel is converted into power. Another third goes out exhaust pipe unused, and remaining third becomes heat energy. A cooling system of some kind is necessary in any internal combustion engine. If no cooling system were provided, parts would melt from heat of burning fuel, and pistons would expand so much they could not move in cylinders (called "seize"). The cooling system of a water-cooled engine consists of: engine's water jacket, a thermostat, a water pump, a radiator and radiator cap, a cooling fan (electric or belt-driven), hoses, heater core, and usually an expansion (overflow) tank. Fuel burning engines produce enormous amounts of heat; temperatures can reach up to 4,000 degrees F when air-fuel mixture burns. However, normal operating temperature is about 2,000 degrees F. The cooling system removes about one-third of heat produced in combustion chamber. The exhaust system takes away much of heat, but parts of engine, such as cylinder walls, pistons, and cylinder head, absorb large amounts of heat. If a part of engine gets too hot, oil film fails to protect it. This lack of lubrication can ruin engine. On other hand, if an engine runs at too low a temperature, it is inefficient, oil gets dirty (adding wear and subtracting horsepower), deposits form, and fuel mileage is poor-- not to mention exhaust emissions! For these reasons, cooling system is designed to stay out of action until engine is warmed up. There are two types of cooling systems; liquid cooling and air cooling. Most auto engines are cooled by liquid type; air cooling is used more frequently for airplanes, motorcycles and lawnmowers. Liquid cooled engines have passages for liquid, or coolant, through cylinder block and head. The coolant has to have indirect contact with such engine parts as combustion chamber, cylinder walls, and valve seats and guides. Running through passages in engine heats coolant (it absorbs heat from engine parts), and going through radiator cools it. After getting "cool" again in radiator, coolant comes back through engine. This business continues as long as engine is running, with coolant absorbing and removing engine's heat, and radiator cooling coolant. A cooling system pressure tester is used to check pressure in cooling system, which allows mechanic to determine if system has any slow leaks. The leak can then be found and fixed before it causes a major problem.
| | Oil / LubricantsWritten by Kevin Schappell
I receive a lot of questions regarding oil and least understood part is number system used to rate oils. Oil weight, or viscosity, refers to how thick or thin oil is. The temperature requirements set for oil, by Society of Automotive Engineers (SAE) is 0 degrees F (low) and 210 degrees F (high). Oils meeting SAE's low temperature requirements have a "W" after viscosity rating (example: 10W), and oils that meet high ratings have no letter (example SAE 30). Oil is rated for viscosity by heating it to a specified temperature, and then allowing it to flow out of a specifically sized hole. Its viscosity rating is determined by length of time it takes to flow out of hole. If it flows quickly, it gets a low rating. If it flows slowly, it gets a high rating.
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