In 2014 Mercedes-Benz introduced a new in-line four cylinder engine for their Sprinter van products (i-4). Like current and future Sprinter-based motorhome owners I was very curious how the new engine would perform once a full motorhome coach was built on the chassis.
Now, under full disclosure, I’m not an automotive engineer. I’m a Winnebago owner who bought a new Itasca Navion in late 2012 and has put over 40,000 miles on it from Canada to Mexico and the Atlantic to the Pacific. My wife Terry and I have driven our Navion over 12,000 foot passes through the Rockies and to the depths of 200 feet below sea level in Death Valley.
Like most motorhome buyers I certainly looked at the vehicle specs like horsepower and torque, but numbers in a brochure don’t even give you a hint about real world performance. Nor do the several test videos of four cylinder Sprinter vans comparisons doing 0-60 tests on YouTube.
A few months ago I suggested the possibility of doing a real world driving test to Winnebago product manager, Russ Garfin. What I had in mind was a stretch of I-70 from Denver to Vail. In the 20 years that we lived in the Vail Valley we’d often see test cars with manufacturer plates driving this stretch of highway. It’s 100 miles each way with several big climbs and it would provide a perfect test for comparing performance.
The route
Our route would be a 200 mile round trip. Starting from Denver at 5,280 feet we would take I-70 west, 100 miles to Vail. Along the route there are several long grades ranging from 4% to 7%. There’s a steep and continuous climb to the Eisenhower Tunnel at 11,018 feet and a descent into the Blue River valley going by the towns of Dillon, Silverthorne and Frisco. There the highway winds and climbs again to 10,666 feet at the top of Vail Pass and then descends 10 miles to Vail. On the return trip the “downs” became “ups”, all of which offered a good challenge for the Navions.
The vehicles
2015 Navion V: 2.1 liter I-4 cylinder 161HP 7 speed transmission
2013 Navion V: 3.0 liter V-6 cylinder 188HP 5 speed transmission
For the test Winnebago built a new 2015 model with the V floorplan which was delivered to our dealer, Transwest, located about thirty minutes north of Denver. To make the comparison as accurate as possible we unloaded EVERYTHING from our Navion, drained all our tanks, and had our local dealer (Mercedes Benz of Westminster) perform the 40,000 mile service. Next, we topped off the diesel tanks in each coach and then drove both Navions onto a public scale.
The I-4 2015 Navion weighed 9,550 pounds and our 2013 weighed in 9,800 pounds. Some of the 250 pound difference can be attributed to our V-6 2013 having HWH jacks and a 1/4 tank of propane. (That weight differential was reduced by about 100 pounds as the the new Navion pilot/co-pilot crew were two bigger guys, our friend Chris and I, while our V-6’s crew were the more petite girls, Terry and our friend Susan.)
Don and Terry Cohen take a break at 10,666′ Vail Pass
The methodology
We topped off each vehicle with diesel and headed out onto the freeway. We would drive at freeway speeds going with the flow of traffic and, as most motorhome drivers do, usually staying in the mid to upper 60’s. We had walkie-talkies to communicate with each vehicle. This was helpful to confirm, on the steep grades, that each driver had the accelerator floored for maximum power. We drove non-stop to Vail and had three stops on the return – two for pictures and video, and one for lunch. Whenever we stopped we turned the engines off so idle time would be the same. Upon our return to Denver we returned to the gas station and topped off both tanks for a mileage check. Our average speed was calculated by total travel time minus breaks and stoppage for road construction.
Trip length: 198.7 miles • Average speed: 54 mph
Driving Impressions
Following the 2015 Navion 24V through Ten Mile Canyon near Copper Mountain
Firing up and rolling out of the parking lot, the i-4 engine engine seemed a little quieter than the V-6 that I’m used to. I don’t know if this perception was a difference in the engine or soundproofing of the new model. Acceleration from a dead stop felt quite similar and, as the coach gained speed on the highway, I felt like there was just a little less engine noise. Pressing down on the accelerator built speed pretty quickly going from 50 to 65. Turbo lag, whether from a stop or accelerating at higher speeds, seemed minimal. The steering felt exactly like the rock solid, no drift Mercedes tightness I’ve become accustomed to in our V-6. As I signaled through city freeway lane changes, the overall handling characteristics felt as “mini-van simple” as they have in all my Sprinter travels.
But what about the “oomph” you’re anxiously waiting to hear about? Within a half-hour we had our first inkling of what to expect. As I-70 leaves the plains of Denver behind it enters the foothills of the mountains with a pronounced climb. The stretch of highway up Mt. Vernon canyon is quite familiar to me from my first drive across it when it opened forty-four years ago when I was 16 and driving a Studebaker, to being a passenger in a 100+ MPH uphill sprint in a supercharger modified Ford Pinto (I think the statue of limitations on speeding has lapsed on that one). As we passed the exit to Buffalo Bill’s grave, Terry led in the V-6 and I followed closely behind in the I-4. As we always do at this grade, we built a little speed on the dip before the climb and then held the accelerator down. I stayed close behind Terry and as we climbed she barely gained any distance. There was plenty of power to match the V-6 and keep us holding at 55 MPH to the crest of the hill at what locals call the “picture bridge” where you get your first view of the snowcapped Rockies and the Continental Divide.
Though I knew we had several grades ahead for further testing, there was both a feeling of relief and excitement that this new engine and seven speed transmission combination might very well become a satisfying option for future Navion and View buyers.
The next big climb was ascending to the Eisenhower Tunnel, which is the highest freeway tunnel in the US. I left the transmission in Drive and let the engine downshift as I held the accelerator to the floor. Again, our ascent closely matched Terry in the V-6 and both rigs managed 50 MPH at the tunnel entrance. As a comparison, in a trip to California a couple of months earlier, our V-6 Navion hit that same spot at 45 MPH with all our gear, full water tanks, and pulling our Honda Fit.
The descent from the tunnel is a long six mile grade with a 60 MPH speed limit where it’s easy to build speed. This was an ideal section to test engine braking with the Tiptronic transmission. I downshifted to 5th gear and watched the tach rev up to about 3,900 RPM. High, but still comfortably below the redline. This held the rig quite steadily at 60 for several miles of the descent, something that the V-6’s five speed transmission doesn’t do as well. I think having the extra range of gearing may make engine braking a little more effective in the I-4 as you have more choice of gears to hold the vehicle back without redlining the engine.
The rest of the way to Vail our experience was similar with the i-4 closely matching the V-6 in climbing power.
On our return trip back through the tunnel we ascended the longest and steepest (7%) grade. The highway is three lanes across and both of the Navions climbed in the middle lane while passing the semis slowly moving on the right. I had my foot to the floor to keep our speed between 50-55. Terry was right behind me and I asked her to move into the far left lane and floor the V-6. Slowly, but surely, I could see her closing in through my side mirror and ultimately passing me. This final test demonstrated that the V-6 appears to have a little more power at the higher end than the I-4.
Don and Terry checking mileage after the test
Fuel Economy
Our focus for this comparison was power, not fuel economy, and although we weren’t doing a “best case” highway fuel test, we did do a careful comparison of the mileage. Pulling into the gas station in Denver we noted our mileage and carefully topped off both tanks. The 2015 I-4 got 17.4 MPG and the 2013 V-6 got 16.5 MPG. Mercedes reports that the 4 cylinder engine should get about 18% better mileage than the V-6. If that’s the case, an owner should expect something closer to 19 MPG in ideal conditions. From my own experience, and in talking with other Navion and View owners, I found that our mileage performance improved a bit after 10,000 miles. A more broken-in I-4 should yield better mileage, but with 40,000 miles of highway experience where, out of habit, I always check our mileage on our V-6 Navion at every fill-up, I’ve seen our mileage range from 11 on the low to 17 on the high. I’ve learned that variables such as wind, rate of speed, and consistency of speed all significantly effect mileage performance.
Summing up
For many, the new Mercedes I-4 will prove to be a satisfying power plant for moving your coach down the road. For hill climbing, without a direct comparison, most drivers won’t notice any appreciable diminishment in power. And even if fuel efficiency is only marginally better than the V-6, you’ll probably save a few bucks on every fill-up and extend your cruising range to the next gas station by 20 to 50 miles. From my observation, the V-6 had a little more top end power, and one might reasonably speculate that, when loaded down with another 1,500 pounds of weight and pulling a 2,500 pound tow vehicle, the pulling and passing power of the I-4 might be less than we experienced in our test drive.
Considering where we live in the Rocky Mountain west, and that we generally pull a tow car, I’ll stick with the V-6. I expect there will be plenty of debate in the View/Navion community similar to generators: some prefer the Onan diesel, and some prefer the LP version. And just like that argument, both options are perfectly viable choices.
At least now for all of us in the Skinnie Winnie world, the big question has been answered: the I-4 engine is definitely up to the task.
Watch the video of the test drive by clicking here.