2008 Mercedes-Benz C300 flex-fuel test drive

What do the rating stars mean?

Performance—both of the speed and acceleration variety, and of the precise handling persuasion—mixed in with a pretty darn cushy ride plus amenities (for an entry level Benz), make this package hard to ignore. Throw in the new C300’s E85 fuel-flexibility and it’s just as hard to resist. Base: $31,200, as tested with premium equipment upgrades, $40,385. EPA estimates: Gasoline: 18 city/25 highway/21 combined. E85: 13 city/19 highway/15 combined. Warranty: 4-year/50,000-mile basic and powertrain plus unlimited 24-hour roadside assistance.

Scott: “For 2008, Mercedes-Benz did a front-to-back redesign of the C-class sedan. It’s a completely new fourth-generation for this popular I-finally-got-the-Benz-I-always-wanted model, and she’s a beauty. I like the more muscular look that the Benz designers laid down for the new C300. Our luxury trim flex-fuel tester had that S-class look—a little wider and rounder and with sharper lines—without quite the ‘wowsy woo’ steep price tag. And then too, with the reasonably sized 3.0-liter V-6, I was thinking we had a reasonable chance of pulling down some decent fuel economy numbers. As is always my goal, I took on the ‘I bet we can beat the EPA fuel economy estimates’ mantra. I get giddy when I can take a car that looks like it'll drink like sailor and then make her sip like a princess.”

Christine: “Good lookin’ from the get-go, my first take was as the delivery crew gave it a final spray-and-shine polish. With two decades’ spread between our ole 300D’s and this new generation, I was looking forward to exploring the interim.”

A little more width, a little more length, and an increased wheelbase make the new C300 lots more comfy while bumping up the cargo space to boot. This one exudes comfort and spaciousness, but not at the expense of nimble agility and “whoa baby” cornering. It’s part of the MB experience. You can get a little lost in the cushiness of the MB Tex covered, power adjustable seats, and the whiz-bang of the joystick-like audio/nav controller can make you smile with a true technocrats glee. But it’s that rock-solid snap-into-the-curve-and-accelerate-like-a-banshee handling that only a true rear wheel-driver, like our tester C, can deliver. And she screams performance! Plant her on the terra firma, nail the throttle—and that suspension,that torque, baby—oh, what a feeling!

Of course that’s not all. This V-6 engine hasn't necessarily been engineered for great fuel economy, as is evidenced by the six's deep, throaty growl when the throttle is stabbed--and then held as the revs spool-up. And spool-up they do, in a steady, when-might-I-run-out-of-revs-kinda-way. Yet surprisingly, the fuel mileage numbers aren't too bad--even with aggressive driving. And let's just say that it is not so easy to behave and go light on the pedal with this package. I (Scott), found my frugal “save gas” mentality doing serious battle with my “Oh hell, let’s have some fun” persona. And the Benz boys certainly didn’t help quell the temptation with the seven-speed manually shiftable bang-em-up-bang-em-down automatic tranny. Oh yeah, did I happen to mention that it's fun?

Time to get serious about fuel mileage. As with all FFVs, fuel economy does take a hit when E85 is in the tank. For a detailed explanation, see our Why Fuel Mileage Drops with E85 article. We wanted to see if the decrease was linear in this car, so we did some experimentation with varying ratios of E85/gasoline. The C came filled with straight premium gasoline (as recommended by Mercedes), and combined driving netted us a decent 23.2 mpg. We ran similar combined trips for a few days till we were down to a half tank, and then topped off with E85.

An interesting aside: Many of the flex-fuel vehicles we’ve driven only required regular 87-octane gasoline when not using E85. This car requires premium 91-octane gasoline, but is still able to run E85. What gives? It’s the ethanol in E85 that makes the difference. Ethanol has an octane rating of about 105, far more than even premium gasoline. So whether your flex-fueler is a performance sedan, or a regular old grocery getter, E85 works in either.

After another couple of days with a 50 percent mix of E85 in the fuel system, and pretty much the same driving conditions, we saw our economy drop to 21.1mpg—about a ten percent dip. Two more days passed before we topped off with E85 again, bringing our fuel ratio to about 75 percent E85. Yet another test run garnered us 19.9 mpg (another 5 percent drop). From these results, and extrapolating out, it looks pretty linear, and on target for a further 5 percent reduction in fuel economy at a 100 percent E85 run. Unfortunately, we ran out of test time and had to return the car.

Though making that final run on 100 percent E85 would have made the results of our C300 fuel test more definitive, we feel pretty confident that the observed economy drop-off would have been very close to what we could estimate given the other results. Assuming an approximate 20 percent (or so) total fuel economy loss on a pure E85 fill-up, is the flex-fuel package worth the price?

Luckily for all of us, the flex-fuel option has a price premium of exactly zero dollars. How does that work? Because a vehicle’s flex-fuel-ability means not much more than some alcohol resistant fuel system parts, a sensor or two to determine fuel makeup and an additional computer algorithm to set fuel calibration, there really is minimal additional cost incurred producing an FFV, and manufacturers usually just absorb it.

With the C300, when does the break-off point occur. When does the reduced cost-per-gallon of E85 offset its reduced miles-per-gallon deficit? According to fueleconomy.gov, the payoff comes immediately. Cost to drive 25 miles on premium fuel: $5.17 Cost to drive 25 miles on E85: $4.78. We think … quite enough said. And oh yes, by the way, we handily beat the EPA estimates on both E85 and gasoline.