A therom fan saves about as much as a viscous coupling. About 3%.
Ford of Germany did tests in 1979 show that there is 3 hp per 100 saved with a viscous coupling over a stock plastic fan. And 3 lb-ft per 110 lb-ft. On a 300 hp engine, maybee 9 hp saved and 330 lb-ft engine, 9 lb-ft.
As Linc has said, the power has to come from somewhere. Real saving is that the normal wind rush above 4o miles per hour allows the fan to be turned off, and you save that 3%, plus the 1.2 hp. Remember, 30 amps at 15 volts is only 450 watts, or just over .6 hp isn't quite true. becasue the efficency of both the electric alternator and the electric fan is apalling at 50%, better than 25% of a engine, but there are two 50% efficent circuits. So 0.6 hp becomes 1.2 hp saving. In terms of miles per gallon, there is half a mile per gallon in just that.
When the thermo fan is off, you gain more than 3 hp over a four blader, plus 1.2 hp in a 100 hp engine. Thats 4.2 hp by doing very little. That's a 4.2% gain, which isn't bad. Just make sure the engine runs cool in grid lock situations.
GM Holden in Aussie used thermo fans in some rear drive cars (A9X Torana SS) from about 1978, and by 1988, all had them. They make a big difference in economy at open road speed, but not that much at low speed. They consume power at low speeds when the thermostat turns them on.
Ford of Germany did tests in 1979 show that there is 3 hp per 100 saved with a viscous coupling over a stock plastic fan. And 3 lb-ft per 110 lb-ft. On a 300 hp engine, maybee 9 hp saved and 330 lb-ft engine, 9 lb-ft.
As Linc has said, the power has to come from somewhere. Real saving is that the normal wind rush above 4o miles per hour allows the fan to be turned off, and you save that 3%, plus the 1.2 hp. Remember, 30 amps at 15 volts is only 450 watts, or just over .6 hp isn't quite true. becasue the efficency of both the electric alternator and the electric fan is apalling at 50%, better than 25% of a engine, but there are two 50% efficent circuits. So 0.6 hp becomes 1.2 hp saving. In terms of miles per gallon, there is half a mile per gallon in just that.
When the thermo fan is off, you gain more than 3 hp over a four blader, plus 1.2 hp in a 100 hp engine. Thats 4.2 hp by doing very little. That's a 4.2% gain, which isn't bad. Just make sure the engine runs cool in grid lock situations.
GM Holden in Aussie used thermo fans in some rear drive cars (A9X Torana SS) from about 1978, and by 1988, all had them. They make a big difference in economy at open road speed, but not that much at low speed. They consume power at low speeds when the thermostat turns them on.
