Buying and Maintaining a Car
A Product Review: Digital Fuel Mizer

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By DuckyDuck
August 7, 2008

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I've read some reviews in the past before ordering it, but I went ahead and ordered the Digital Fuel Mizer at

I even have the "DFM-2", the newer version, supposedly better than the original, but all this product is is an accelerometer, programmed with a set of LED's that light up and a speaker that beeps if you accelerate or even decelerate too hard.

We know that "jackrabbit" starts, or for that matter both starting and stopping too fast wastes fuel. So this is just a nagging box that can tell if you're accelerating and/or braking too fast. The braking nagging will really help try to turn you into a hypermiler, or that is, learning how to coast to a stop or anticipate slowdowns and required stops.

So I bought one and tried it.

Actually, I've already been trying to drive like a hypermiler with gradual starts, lots of coasting and little use of the brakes. So really, the little gizmo didn't beep at me all that much except for a few surprise stops on the road (animal darts in front of the car, someone changing lanes without seeing me, etc...).

The little box has two red, two yellow, and two green LED's. The owner's manual tells you to drive to just keep the green LED's lit and not the yellow or red. However, I was already driving like that, so I'd back off a bit further and try not to make either of the two green LED's light up if I could control myself further.

My around-town driving didn't change much, really. It was highly variable, between 28 and 36, and especially if my babysitter had quite a few errands. I wasn't going to be able to do a full-tank test that easily, considering she was driving my xB almost every other day during the summer.

However, I went on a trip this weekend to visit my relatives. That gave me the opportunity to try out driving with this gadget on full tanks driven only by me. I wasn't going to be doing highly-analytical and scientifically controlled conditions here. It's just that over that last year, my mileage would range from 26 to 32 MPG, driving combinations of I-80, I-94, I-80/90 Toll Road, I-69, and US12.

So this was just a a "seat of the pants" estimation on how well it controlled my driving.

On the way down, I topped off the gas tank in Saline (MI), and then went west on US12, south on I-69, and west on I-80/90 to west on I-80 to Exit 127 in Illinois (Houbolt Road/Empress Road). Although most of the time, the cruise control was used, there were several areas in which I had to slow down and accelerate or decelerate as needed. Mileage: 38.2 MPG.

From Exit 127, I continued on I-80 across Illinois, onto I-280, then off onto two-lane roads to Andalusia, IL, and stopped and refilled my gas tank there. Mileage: 34.3 MPG.

On Sunday, topped off the tank (during the weekend I ran around town and burnt off a couple gallons, got around 33 MPG. Leaving Andalusia, I was bored of driving I-80 east, so I decided to take US6 across Illinois, driving through several small towns and going 55 MPH the whole way. I got off US6 up Empress Road and gassed up at the same gas station on Exit 127 on I-80. Mileage: 40.07 MPG!

The last leg was a home-stretch dash, from I-80 to I-94 in Michigan, going 70 MPH most of that leg. I stopped at Exit 169, Zeeb Road and filled up, mileage: 38.7 MPG.

So do I feel it made a difference? A little bit. Again, I was already driving more conservatively over the last year, so much so that I almost never made the yellow LED's go off, ever.

Another quirk, if you live on a gravel road or a very BUMPY road (your county or state has badly paved roads), then this thing is useless because it will go off (beep into the RED LED's) on every bump.

Do I think it's worth it? To me, not all that much, as I already drive "conservatively". It would be worth it to someone who has no clue as to how fast or slow he accelerates compared to how one SHOULD drive to get the best mileage. But I think it would REALLY be worth it to parents of teenagers, just learning to drive and teaching those kids the most economical way to drive.

As for other details, it's just a small metal box; it can sit on your dash or steering column (they want it within 15 degrees of horizontal) and has Velcro strips if you want to attach it that way.

I think a lot of these will come back onto the market, like on eBay, because once one is "trained" to drive to accommodate the lights and beeping, you may be able to drive that way from now on.