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Updated Automatically on October 23rd, 2008
better gas mileage

Is your gas mileage being blasted by your car stereo?

If you have a “killer” car stereo, you could be killing your gas mileage when you play it loud. OK, I admit it, I have a car stereo that can create rock concert volume levels. It has nine speakers, including a huge subwoofer, and over 700 watts of power from multiple amplifiers. In my defense, I don’t play “thump-boom” music on it, I play classic and alternative rock. (OK, not much of a defense, but it does sound good.)

A car stereo like mine can dim the car headlights if played at high volumes. It can drain the car battery quickly if I play it loud with the car off. All the power to run a monster car stereo has to come from somewhere, and it comes from your gas tank.

A few hundred watts of extra load on the alternator means you’ll be getting worse gas mileage because your car has to burn more fuel to supply the power for the stereo.

Turning down a powerful car stereo will not only save your hearing, it will improve gas mileage.

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Updated Automatically on October 23rd, 2008
better gas mileage

10 Responses to “A Booming Car Could Be Busting Gas Mileage!”

    Is this proven? I had always thought the alternator ran at the same speed no matter how much it happened to be charging the battery.

    If your engine is always turning 2500 RPM, then the alternator will always be running at the same speed. The issue is with how much energy it takes from the engine to turn the alternator.

    The load that the alternator places on the engine varies according to the load the electrical system is placing on the alternator. If you’ve ever seen your headlights dim a bit or heard the engine slow slightly when you turn on your heater fan or rear window defogger, you’ve seen the effects of increased load on the alternator. The engine will usually idle itself back up a bit to compensate for the increased load, and that consumes more gas.

    The more power load you put on the alternator, the worse your gas mileage will be. The energy to run a big car stereo has to come from somewhere, and it’s coming from your gas tank.

    Well, booming your music does not effect mpg, it’s that simple. The alternator is producing it’s output in accordance to the engine RPM and the alternator’s rated amperage, whether more load is placed on the charging circuit of the car, the same mechanical load is placed on the engine from the alternator no matter how much power your stereo is pulling from it. The only reason your lights dim is because most of your power is suddenly going to your amp and that gives everything else less electrical power to do what they were doing before the bass hit. Either up the gauge of your charging circuit wiring, or spend $80 and grab a 1f capacitor for your amp. Oh, also, a way to prove that your alternator is not varying the mechanical load on your engine is to watch your rpms when you have a big bass hit, they stay the exact same, the only reason your ac consumes mpg is because the compressor is spun from the pully which is applying more load when it’s turned on. Whether you turn your cab fan on or off, there is no rmp slowdown or anything, maybe a little electrical strain, but that’s just gonna effect your head lights by a few lumens.

    Sorry, Someone, you are not right. If the alternator has No load on it, it won’t take much engine power to turn it.
    But if there is a big load on the alternator, the current it’s producing is created by mechanical effort, that is resistance to turning and hence drag on the engine.

    Alternators are not a source of free power!

    I just bought a new Civic Hybrid and I would Love to know if I put a couple of subs and a amp in it would it affect the batteries behind the seat with the constant pounding? Also there is only a tiny battery under the hood for “emergency” back up to start the car because the car is started from the electric engine which is powered by the battery behind the seat.

    “Someone” is correct, the stereo does not .directly. cause more fuel to be consumed. The alternator does not have a varying mechanical load like an air conditioner…. Although you could be weakening the engines ability to generate a nice fat spark which could effect performance and therefore effect mileage. So you are both right. “Admins” theory is correct, but the reasoning is not. “Someone’s” reasoning in regards to alternators is correct but I would suggest that there could be a drain on the autos ability to generate nice healthy fat spark, if “admin’s” vehicle is a diesel he’s got some major issues beyond explanation. ]

    I agree with the last post. Someone’s statements are breaking the first law of thermodynamics. Since the only energy contained in the sound system is in the capacitors that dissipate quickly once shut off, one can only conclude that the energy the system converts to sound must come from the car’s alternator. The load of the alternator on the car will vary with the system’s requirements.

    An interesting way to view this is by assuming that each drop of gasoline will produce a certain amount of energy. That energy is divided among the car’s various systems including moving forward, AC, lights and stereo to name a few. If the stereo is shut off, less energy, and hence, less gas is required to operate the remaining systems.

    Hope I didn’t confuse anyone…


    i know for a fact that it drains power. on my 04 dodge stratus 2.7l v6, it gets 24 in the city. when i decide every once in a while to hook up my pos and my ground to my 760 watt pioneer and subs to enjoy a lot of bass, im also killing power and losing gas mileage. my second and third gear drag like none other and my gas mileage drops down to about 17.8 miles a gallon. HAVING A LEAD FOOT ISN’T A GAS GUZZLER, BUT HAVING A NICE SYSTEM IS.

    basically if you use 5,000 watts to pump a system that drain comes straight from the fuel tank, as Mark said. As the load on an alternator increases it gets harder to turn and that resistance to the engine takes off horsepower 746 watts equals 1 horsepower a 5,000 watt drain would equal 6.7 horsepower but the typical alternator is only 65% efficient so the actual toll from said 5k system (which would be continuous and LOUD) would be 11 horsepower . you do the math on what your car takes to fun your stereo and you find that its not that much until you get into the competition range.

    Agree with the previous post. The effect of a subwoofer is not significant on gas mileage. The weight, however, might be. My system is very heavy - I can barely lift it out on my own. Anybody have any input on this?

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