On my last trip from norcal to socal I left the headlight on all the way. I set the cruise at about 80mph but I got worse MPG. The trip previous to that I got 34.xxmpg. This last trip I got 32.0xMPG... AC was on for both trips.

Anyone else experience this?

 

I can not see how headlights change MPG look for something else as the variable

 

Headwind/tailwind may have been a factor also?

 

The law of conservation of energy will tell you your MPG must be affected by any powered device in the car. But I doubt it would be 2mpg. Probably some small fraction of that can be attributed to the headlights. I'd guess some environmental factor was at play?

 

The photons from the headlights slow the time down as the car travels through the path of the photons traveling at the speed of the light. Therefore, the velocity of the car has to be recalculated accordingly. Because less time is spent to travel the same distance, the speedometer reading is slower than it is.

miles/gal = miles/hour x time spent x 1/fuel used.
Therefore, as the speed goes up miles/gal improves. So you get better mpg with the headlights on.

 

 

Agreed

 

i'd look to blame winds, or maybe a change in elevation from point A to point B. interesting though.

 

well that's what I did wrong. I didn't go fast enough

 

Now it all makes sense.

 

Yur wax job is wearing off. Everyone knows a freshly waxed MINI slips through the air with less resistance than a not-so-lately-waxed MINI. Unless of course you speed shine just prior to the trip. You have to clay bar too because those little hard to see particles all slow the MINI down.

 

With anything on, your alternator is providing great load for the motor to work against. As some one else said, I would be surprised that it took as much off the fuel consumption as was stated by the OP.

 

Wow... just.... wow

 

why just wow?

you've never made any threads in jest before?

 

is he really serious?

 

"Zat ist CRAAAZY!!!!!"

 

In practical application this isn't necessarily the case, though. Your alternator is causing loss on the drive system, true, but it may be creating extra electricity in the system that is simply going to waste. Adding another electrical device can use up some of that waste with no further loss in the system.

I remember an article in the paper when daytime running lights were first being implemented in the US. The manufacturer, in this case GM, predicted that the lights being on all the time might consume, at most, 2 gallons of gas over the life of the vehicle.

 

If you were using Auto A/C with the same internal temp setting both times, ambient temp and sunlight vs. overcast could affect the amount the A/C comes on.

The amount of traffic could also affect mpg. Did you have to disengage cruise control on either trip because of traffic?

 

I hope so. Otherwise I have been driving under a misconception with my lights on for years.

 

several times. i don't remember when i didn't have to disengage on that trip. it's about 320miles on the freeway for me so i'm bound to hit traffic where i have to slow down.

 

Light has mass. The thrust from pushing the light out of the front of the car slows the car down significantly. The lights also give off heat, which causes the air molecules in front of the car to become agitated, and the friction slows the vehicle down even more.

Relocating the headlights to the rear of the vehicle should greatly increase your gas mileage. As an added side effect, it also makes it easier to back up at night.

 

I would say not considering the OP's response above.

 

i could not verify cos my daytime running lights is always on...

 

I'm not an engineer, but from my old Cobra racing days it was felt that the more drain that you put on your electrical system, the harder the alternator has to work. The harder the alternator has to work takes more horsepower to turn the alternator. Hence in race cars quick recovery batteries to take the load off of the alternator. If there is someone out there who can confirm this I would appreciate it. I know that when Throw an extra draw on the electrical system in the mini I can temporarily here the RPMs drop slightly. This to me would indicate the extra load.

 

I remember reading in PM that daylight running lights can reduce mileage by .1 MPG.