I'm sure this test has been done a million times, but I wanted to see for myself. I ordered LED's to replace all auxillary lights on my '97 s10 2.2 liter, as well as the 10 additional 194ll marker lamps on my tool box. But before I went and installed them I figured I should get some really good data points so I could quantify my results. So, here I am almost 4 hours later and 180+ miles driven with some suprising results (suprising to me at least).
Testing method: A outbound/inbound B outbound/inbound A outbound/inbound
My new Scanguage II cam in yesterday and I've been playing with it a ton. Drove about 300 miles on it when we went houseshopping so I got a handle on it. I calibrated it (needed very little adjustment) at 1/4 tank yesterday and verified that with a fillup this morning.
So I wanted to see what kind of mileage difference running all of them bulbs did. This morning I got up early and found a nice, flat, and smooth stretch of 4 lane out of Omaha that is not very well traveled. I decided to use from one turn around point to another turn around point as an easy test ground.
My grilfriend set the scanguage trip at the designated mile marker on the outbound trips, and the desgnated lightpoll on the inbound trip. Verified distances with GPS (15.5 outbound, 15.7 miles inbound). I was going 60 for about 1/8th of a mile before she hit the trip.
We did one trip with headlights/marker lams on. (A1 outbound, A1 inbound)
Then we followed up immediately with no lams on as I disconnected the DRL. Fuse 15 for fellow s10 owners without factory fog lamps. (B1 outbound, B1 inbound)
We then reinstalled the fuse and turned on the marker lamps for a verifying run (A2 outbound, A2 inbound).
The B test was then duplicated again.
Results were suprising. According to my limited data all of those bulbs combine to suck about 1.05mpg at highway speed. This is about 3x's as much as I expected.
See graph below:
Edit to add: 32.5 - 31.55 = 0.95 (not 1.05) Thanks Darcane!
Now I realize that there are several areas that made my testing less then perfect. First, because it took over 3.5 hrs to complete, the temp had changed about 15 degrees from begining to end. However, the final "B" run still came in about the same below the "A" runs.
Also, there was some traffic (maybe 2-3 cars per run both directions). All of these cars drove by at a pretty steady rate and none of them gave me a "draft." I did not get affected by any semi's on my runs this morning.
There is some slope to the course. According to the GPS the course drops about 60 ft during the inbound run. Of course, this should effect both A & B equally.
I don't have cruise control. I tried to hold a steady 60, but that is impossible without a perfectly flat course. According to the GPS, my avg speed for all 3 runs was exactly 60. I did get up to 61 on all the runs, and even 62 on the "B inbound."
Wind. There was some wind this morning, but my course was parallel to it for the most part. This is Nebraska, and if I waited for a day with no wind I'd never get any testing done.
Weight. I burned about 4.5 gallons of gas from begining to end. This seemed to have no impact on the results, because the last A run still fell in under the B run. Even though run "A2" should have had all of the same advantages it still fell well under the "B1" run.
Conclusion:
Having the headlights/marker lights off improves gas mileage 1.05mpg @ 60mph. I am really shocked that 1.05mpg went to powering all of my lights!
I wanted to make my test as valid as possible, but this was my first time out. If there is something I did wrong, either in the test or data collecting please let me know. I want my results to be valid, but I don't have lab equipment to play with.
I learned alot from this expirment. The DRL is getting permenantly deleted, and I'll just run with 100% LED's driving/maker lights on during the day. This should cut about 98% of the wattage I am using currently (DRL's+marker on).