When we first reported on the Fuel Doctor FD-47 last December, we said the $50 to $60 device—which claims to boost fuel economy by as much as 25 percent—failed to deliver any benefit in our tests. The manufacturer challenged that conclusion, saying we should have used different test procedures and older vehicles. So we recently ran a new set of tests deliberately designed to reflect many of the manufacturer’s recommendations.
Bottom line? Our conclusion remains the same: No improvement in miles per gallon with the FD-47. We continue to rate the Fuel Doctor a “Don’t Buy: Performance Problem.”
The Fuel Doctor is a cylindrical device that plugs directly into your vehicle’s 12-volt power outlet. The version we tested last year was the Fuel Doctor FD-47. The current one, called the Fuel Doctor Platinum FD-47, is similar in appearance to the original. When we opened the Platinum up, most of the internal electrical components—which used to be visible—are now encased in a black plastic-like material.
Our new tests were conducted to address some of the criticisms that Fuel Doctor LLC made on its website and in direct communications to Consumer Reports following our earlier report. “We take manufacturer comments very seriously,” says David Champion, Director of Consumer Reports Auto Test Center, “and in this case we decided to see if the points raised by Fuel Doctor made any difference.”
One specific complaint had to do with the age of the vehicles tested.
The Fuel Doctor is recommended for vehicles two years old and older, though the information inside the package of the original model we bought also claimed the device had "very positive" effects in terms of lower fuel consumption, increased horsepower and reduced emissions in many of the vehicles the manufacturer had tested that were less than 24 months old.
Our earlier evaluation, in which we ran fuel economy tests on six vehicles and our standard acceleration exam on another four (some versions of the story mistakenly said all tests were performed on all vehicles), involved mainly newer vehicles. The two older ones we included (one had been purchased 26 months earlier, and the other 28 months earlier) were part of the acceleration test group.
Fuel Doctor immediately challenged this choice of test vehicles. Its website quoted Chief Technology Officer Douglas Hungerford as saying, “FD-47 is targeted for use on vehicles 24 months and older--our packaging clearly states this. Since Consumer Reports tested FD-47 on newer vehicles, it is not surprising that their brief testing did not yield significant differences.” So in March, we ran our city and highway fuel tests on four older vehicles (ranging from the 2002 to 2007 model year) and found no meaningful differences when using the FD-47.
Those results had not yet been published when we heard in April directly from a senior company official. He complained about our use of newer vehicles, but also argued—among other things—that CR’s standard fuel economy tests were not the right way to test the Fuel Doctor, even for older cars.
In its various statements, Fuel Doctor has offered slightly different versions of this point. But, basically, the company says you have to drive a car for a certain distance with the Fuel Doctor installed before fuel economy can be measured. Its website challenge to Consumer Reports, for example, says a valid test of its device would require that vehicles be driven at “65 miles per hour and 150 miles for each vehicle without the FD-47 and 150 miles with the FD-47 plugged in. And no instant measuring of fuel consumption reduction without the product being engaged throughout at least one full tank of gas cycle.”
Hungerford’s comments on the website explain the rationale for this procedure: “The FD-47 works by cleaning and conditioning the power of a vehicle’s electrical systems. Conditioned and clean power allows the vehicle’s electronic control unit (ECU), fuel injection and engine timing equipment to operate more efficiently. When the vehicles engine runs more efficiently it will require less fuel, produce more power and have reduced exhaust emissions (CO2).” The extended driving time with the device installed is necessary, he says, to allow “time for the vehicle’s electronics to adjust to the cleaner signals as a result of the FD-47 power conditioning.”
Thus, for our third and latest round of tests, which also used only older cars (2002-2007 model years), we made additions to our test procedures to reflect recommendations like those above.
Specifically, we tested the four vehicles shown at right: a 2007 Hyundai Santa Fe with 74,836 miles on the odometer, a 2002 Subaru Forester (102,944 miles), a 2006 Jeep Wrangler (48,966 miles), and a 2007 Volkswagen Jetta (63,255 miles).
Each vehicle was first driven for at least 150 miles at around 65 miles per hour with no Fuel Doctor installed. We then attached a sensitive fuel meter to each car’s gas line and ran them through our standard city and highway fuel-economy tests in order to establish a baseline (i.e., pre-Fuel Doctor) miles per gallon for each car.
Next, we removed the fuel meter and plugged the Platinum FD-47 into the 12-volt power port closest to each car’s engine, as the product’s packaging directs. Starting with a full tank of gas, we then drove the vehicle until either the fuel warning light came on or the needle pointed to “Empty.” The mileage driven ranged from 284 miles to 407, depending on the vehicle’s fuel economy and tank capacity, but the drive always included at least a 150-mile stretch at around 65 mph. We then re-attached the meter and ran our fuel-economy tests again with the FD-47 still installed.
Finally, we removed the FD-47 and took one more set of fuel economy measurements. Thus, for each vehicle we had three sets of city and highway fuel results: a baseline reading without the FD-47, a reading after driving for one tank of gas with the device installed, and a final reading without the device.
The results, again, show no meaningful difference in average city or highway fuel economy for this group of cars (see chart below).
So, overall, we have to conclude that the Fuel Doctor simply does not help you squeeze more miles per gallon out of your car. If you want better fuel economy, Consumer Reports recommends you stick to tried and true methods like driving more slowly and avoiding hard acceleration or braking. For more, see "How to get the most MPG now".
Test results for the Fuel Doctor Platinum FD-47
|Vehicle ||Initial mileage ||Average fuel economy (city/highway MPG) |
|Baseline before FD-47 ||With FD-47 installed ||After FD-47 was removed |
|2007 Hyundai Santa Fe || 74,836 ||11.7/24.7 ||11.5/24.6 ||11.7/24.4 |
|2006 Jeep Wrangler ||48,966 ||10.5/19.7 ||10.5/19.2 ||10.8/19.1 |
|2002 Subaru Forester ||102,944 ||14.9/27.5 ||15.0/27.6 ||14.8/27.7 |
|2007 Volkswagen Jetta ||63,255 ||16.3/33.6 ||16.0/33.2 ||16.2/33.1 |