Hello. I was told that using heater in Winter causes slightly lower gas mileage(MPG). I am not sure if this is true or if I agree as what difference would there be to cause lower MPG ? Instead of coolant(in this case I probably should call it heatant)just circulating thru engine it when using heat circulates a bit further into heater core device. Kind of the same non logic as thinking using more electric(lights on, radio, fan, etc.)would cause lower MPG which of cause it wouldn't as alternator still gets turned regardless of how much or little electric you are using. Only accessory that I know would cause lower MPG would be Air Conditioning as then AC compressor gets turned and this requires more engine power so MPG is lower. Comments & input please. Thanks.