fuel useage of head lights?

[Ryland]

Thanks Vwbeamer, so it looks like your 120 watt load drops your mileage by .01 gallons per hour, last I figured it out my average speed over the last 30,000 miles was around 35mph so 857 hours and a .01 gallon per hour increase in fuel used 8.5 gallons of gas over the last 30,000 miles, so if I put LEDs just in my running lights and kept using them in every car that I own from now on they would pay for them selves many times over.
same thing if I chose not to have a big amp on my radio, or to keep my vent fan on high all the time (over 70 watt draw if I remember) and of course your battery will last longer, alternator, everything, but the point of this thread was to find out how an electrical load affects your gas mileage.

[shovel]

I'm going to keep my headlights on, but then I'm fine with fuel mileage in the 20's for a 4x4 and 40's for a small car. Economy interests me, but it's far from an obsession.

As a related note, for anyone with an S10 and daytime running lights if you don't want to go to the effort of disabling them permanently, you can disable them per-session by pressing the "dome cancel" button 4 times in quick succession.

[wagonman76]

I'm sure it mostly depends on how efficient your vehicle is to start with. I have never noticed any difference with headlights on or off, even high beams. I have tried looking for a difference too in mpguino readings, but none. I get my best mpg at night anyway because I slow down a little more, not just for mpg but also because the deer are harder to see.

[almightybmw]

With the old 4-cyl protege, headlights dropped me by 1mpg. It was a gutless motor with AWD, little things impacted it. In my GP, it has oodles of torque, headlights make no difference. In fact, I've gotten my second best mileage at night (mostly because there was no traffic to bother with). The truck has such rediculous terrible areo that I could run 4 100W offroad lights and it would return the same mpg.

It truly depends on the vehicle. Hence basjoos with his 2-3 loss, his awesome areo anything small has a huge affect.

[shovel]

Originally Posted by almightybmw

With the old 4-cyl protege, headlights dropped me by 1mpg. It was a gutless motor with AWD, little things impacted it. In my GP, it has oodles of torque, headlights make no difference. In fact, I've gotten my second best mileage at night (mostly because there was no traffic to bother with). The truck has such rediculous terrible areo that I could run 4 100W offroad lights and it would return the same mpg.

It truly depends on the vehicle. Hence basjoos with his 2-3 loss, his awesome areo anything small has a huge affect.

This is an excellent example of why MPG is a terrible way of discussing fuel saving modifications.

No matter what kind of car you have, or what efficiency it has, a 55 watt light bulb is going to use 55 watts of electrical energy or roughly around 1/120th of a gallon per hour. Whether you drive an 85 dodge 1-ton or a torpedo shaped civic, 55 watts load on the alternator will be very nearly the same on any vehicle, and will burn very nearly the same amount of fuel. With 2 conventional headlights on, every 60 hours of driving you'll burn roughly 1 gallon of gasoline as a result of the headlights. I illustrated that in my post above. No matter what kind of car you have.