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Using Heater Lowers MPG ?? 700 1988

posted by  someone claiming to be lummer57 on  Mon Dec 15 02:46 CST 2008 [RELATED]

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.








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    Using Heater Lowers MPG ?? 700 1988

    posted by  someone claiming to be kyle245 on  Mon Dec 15 03:30 CST 2008 [RELATED]

    The alternator will require more energy from the engine as its electrical load increases.

    Once I had a loose alt. belt that would only make slipping noises right after the engine was started (because the alternator was recharging the battery) and also when there were a lot of accessories on. When using a alternator tester you put a load on the alternator to see max amperage output at 12 volts. As you increase the load you can hear the alternator require more engine power to turn the alternator. A loose belt will usually squeal when doing this.
    But with the heat on, the only accessory is the fan.








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      Using Heater Lowers MPG ?? 700 1988

      posted by  someone claiming to be lummer57 on  Mon Dec 15 08:50 CST 2008 [RELATED]

      Thanx for reply Kyle245. Very very interesting. I had always thought that alternator/electric usage does not effect MPG. I guess the more electric you use then the more physical(not electrical)strain you put on alternator and thus get a bit lower MPG ?? What physically/mechanically changes in alternator or wherever when more electric is used ?








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        Using Heater Lowers MPG ?? 700 1988

        posted by  Blue Horse on  Mon Dec 15 09:21 CST 2008
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        The alternator works by rotating an electromagnet in a coil. When more current is being drawn, there is more magnetic resistance. I think I heard somewhere that an alternator can create up to 5 HP worth of drag.

        To answer your original question, if the thermostat is working correctly, running the heater should not increase your fuel consumption. If you are seeing lower mileage, it's probably due to winter blend gas, which contains additional oxygenates (usually ethanol)








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          Using Heater Lowers MPG ?? 700 1988

          posted by  someone claiming to be lummer57 on  Mon Dec 15 11:19 CST 2008 [RELATED]

          Thank you Blue horse for your explanation of alternator functioning and also about heater effecting mpg. I wish I were 1/10 as knowledgeable as you and other folx here on Brickboard.








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    Using Heater Lowers MPG ?? 700 1988

    posted by  oldyellr on  Mon Dec 15 03:18 CST 2008
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    I would bet that using the heater wouldn't hurt your gas mileage by any amount you could measure. Yes, it would use some engine heat, but since that's thermostatically controlled, it just means the cooling fan has to work less. Other accessories using power would be the blower fan and the rear window defogger. The latter probably draws significant current, so I would turn it off before it times out if it's no longer needed. However, all of the above loads are probably quite insignificant compared to the way you drive.







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