What all devices in prius will affect gas mileage?

John in LB · 01-10-2007, 05:35 PM

I can't speak for really cold places (like San Francisco... tee hee), but here in Los Angeles, if you are on the freeway, your IC engine is always producing excess heat as part of the combustion process. It is hard to believe, but only 25 to 30 % of the energy in the fuel is used to move the car. The rest of the energy is just converted to waste heat that must be gotten rid of.

Part of the waste heat goes out with the hot exhaust to the tailpipe. The majority is transported via the coolant to the radiator in the front of the car.

When you raise the temperature in the climate control system, some of the hot coolant is diverted to a small radiator underneath the dash. The air passes over this small radiator and heats the passenger compartment. This is how every normal car operates, and I am assuming that this is the same in a Prius.

So, using heat for the passenger compartment will not use up any energy (at least while the engine is running - such as on the freeway). In fact, you could think of it as increasing the efficiency of the engine, since some of the waste heat is being put to good use.

ScottY · 01-10-2007, 06:41 PM

John,

Those of us who live in the northern states will think otherwise. (you lucky bastard! :P )

This morning's outside temp was in the 30's. During first couple of miles, if I set my cabin temp to 70 and wait at a red light. The ICE will need to kick in to provide heat. Fuel is being consumed but car is not moving, MPG = 0!

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01-10-2007, 05:35 PM	#11
John in LB Life is good Join Date: Aug 2006 Location: Orange County Posts: 313 My Car: 2006 Prius Model: Package: #8 Thanks: 0 Thanked 0 Times in 0 Posts Friends: 0	I can't speak for really cold places (like San Francisco... tee hee), but here in Los Angeles, if you are on the freeway, your IC engine is always producing excess heat as part of the combustion process. It is hard to believe, but only 25 to 30 % of the energy in the fuel is used to move the car. The rest of the energy is just converted to waste heat that must be gotten rid of. Part of the waste heat goes out with the hot exhaust to the tailpipe. The majority is transported via the coolant to the radiator in the front of the car. When you raise the temperature in the climate control system, some of the hot coolant is diverted to a small radiator underneath the dash. The air passes over this small radiator and heats the passenger compartment. This is how every normal car operates, and I am assuming that this is the same in a Prius. So, using heat for the passenger compartment will not use up any energy (at least while the engine is running - such as on the freeway). In fact, you could think of it as increasing the efficiency of the engine, since some of the waste heat is being put to good use.

01-10-2007, 06:41 PM	#12
ScottY Senior Member Join Date: May 2005 Location: Long Island, NY Posts: 1,249 My Car: 2005 Prius Model: Package: #3 Thanks: 0 Thanked 2 Times in 2 Posts Friends: 1	John, Those of us who live in the northern states will think otherwise. (you lucky bastard! :P ) This morning's outside temp was in the 30's. During first couple of miles, if I set my cabin temp to 70 and wait at a red light. The ICE will need to kick in to provide heat. Fuel is being consumed but car is not moving, MPG = 0!