Internal combustion engines run on heat. Chemical energy in the fuel is transformed into thermal energy when the fuel burns, which produces mechanical energy to push the pistons, spin the crankshaft and drive the vehicle down the road.
As efficient as today's engines are, they still waste a LOT of the heat energy they produce. The average gasoline engine is only about 22 to 28% efficient. That means over two-thirds of the heat produced by each gallon of fuel either goes out the tailpipe or is soaked up by the engine itself. Diesels squeeze a little more bang out of each buck's worth of fuel with efficiently ratings of 32 to 38%, but even that leaves a lot of waste heat that must be managed and carried away by the cooling system.
Ironically, the hotter an engine runs the more efficient it becomes. But there's a limit because aluminum pistons and heads can only get so hot before they start to soften and melt. The same goes for cast iron. Engineers have been tinkering with exotic ceramic materials and metallic-ceramic alloys in an attempt to build high temperature, super efficient engines. They've realized some significant gains but ceramics are still too expensive for everyday applications.
HOW HOT IS TOO HOT?
Most engines today are designed to operate within a "normal" temperature range of about 195 to 220 degrees F. A relatively constant operating temperature is absolutely essential for proper emissions control, good fuel economy and performance.
A 50/50 mixture of water and ethylene glycol antifreeze in the cooling system will boil at 225 degrees if the cap is open. But as long as the system is sealed and holds pressure, a radiator cap rated at 15 psi will increase the boiling temperature of a 50/50 coolant blend up to 265 degrees F. If the concentration of antifreeze to water is upped to 70/30 (the maximum recommended), the boiling temperature under 15 psi of pressure goes up to 276 degrees.
So does this mean a cooling system with a maximum concentration of antifreeze in the coolant (70%) can run as hot as 276 without boiling over? Theoretically yes -- but realistically no. The clearances in most of today's engines are much, much closer than those in engines built in the 1970s and early 1980s. Piston-to-cylinder clearances are much tighter to reduce blowby for lower emissions. Valve stem-to-guide clearances also are closer to reduce oil consumption and emissions, too. Plus, many engines today have aluminum heads with overhead cams. Such engines don't handle higher than normal temperatures well, and are very vulnerable to heat damage if the engine gets too hot.
Anytime temperatures climb beyond the normal range, the engine is running in the danger zone.
As efficient as today's engines are, they still waste a LOT of the heat energy they produce. The average gasoline engine is only about 22 to 28% efficient. That means over two-thirds of the heat produced by each gallon of fuel either goes out the tailpipe or is soaked up by the engine itself. Diesels squeeze a little more bang out of each buck's worth of fuel with efficiently ratings of 32 to 38%, but even that leaves a lot of waste heat that must be managed and carried away by the cooling system.
Ironically, the hotter an engine runs the more efficient it becomes. But there's a limit because aluminum pistons and heads can only get so hot before they start to soften and melt. The same goes for cast iron. Engineers have been tinkering with exotic ceramic materials and metallic-ceramic alloys in an attempt to build high temperature, super efficient engines. They've realized some significant gains but ceramics are still too expensive for everyday applications.
HOW HOT IS TOO HOT?
Most engines today are designed to operate within a "normal" temperature range of about 195 to 220 degrees F. A relatively constant operating temperature is absolutely essential for proper emissions control, good fuel economy and performance.
A 50/50 mixture of water and ethylene glycol antifreeze in the cooling system will boil at 225 degrees if the cap is open. But as long as the system is sealed and holds pressure, a radiator cap rated at 15 psi will increase the boiling temperature of a 50/50 coolant blend up to 265 degrees F. If the concentration of antifreeze to water is upped to 70/30 (the maximum recommended), the boiling temperature under 15 psi of pressure goes up to 276 degrees.
So does this mean a cooling system with a maximum concentration of antifreeze in the coolant (70%) can run as hot as 276 without boiling over? Theoretically yes -- but realistically no. The clearances in most of today's engines are much, much closer than those in engines built in the 1970s and early 1980s. Piston-to-cylinder clearances are much tighter to reduce blowby for lower emissions. Valve stem-to-guide clearances also are closer to reduce oil consumption and emissions, too. Plus, many engines today have aluminum heads with overhead cams. Such engines don't handle higher than normal temperatures well, and are very vulnerable to heat damage if the engine gets too hot.
Anytime temperatures climb beyond the normal range, the engine is running in the danger zone.
good info
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