Fuel Economy

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Permalink Reply by WDSMGuy on May 27, 2009 at 10:49pm

The best we've documented is 41.25. That was highway last week with 92 and 93 octane gas. The worst we've written down was 30.80 on 89 octane ethanol in December. All of these are with the top on our Cab up. When I started running with the top down last week at 70-75 through Indiana and Illinois the mileage dipped to the high 20s by what the SWAG I could gather from watching the gas gauge. Surprisingly, I averaged 37.6 running 70-75 with the top up and the air conditioning on.

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Permalink Reply by mr bad example on May 28, 2009 at 12:57am

my last tank was 49.5MPGs, since the temps are over 50F i get 45-49 mpgs in my daily stop and go commutes (12.3 miles, 24mph avg speed) my worst tank was the first in january 2008, 37mpgs, my best trip was last week at 79F 61.6mpgs. i use a scan gauge II, it helps me monitor throttle and gear choices.

during the winter in sub-freezing temps my mileage drops to low 40's, the smart takes almost half the trip to get up to 188F, optimum coolant temp. if the coolant goes over 190F, the fan comes on and kicks the idle fuel consumption from 0.18-0.20GPH to 0.30GPH. same when the coolant temp is below 180F.

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Permalink Reply by Ian Pellant on June 13, 2009 at 1:11am

... I haven't posted for a while. The smart has been a dream and no problems whatsoever.

Initially, fuel consumption was highly variable between 5.5 and 7 lhk (US 42.8 to 33.6 mpg)

What has been interesting is to experience the breaking in. As the engine passed the first 1,000km it started to produce a bit more power and became happy at 60kmh in 5th gear. Auto program would not hold at less than 80kph. Fuel consumption on a trip was around 5.5lhk (42.8 US mpg) but around town, 6.5lhk (36.2 US mpg) was the norm... that's the sticker consumption for the pulse turbo in city conditions. Auto shift was herky jerky from standing start, but brilliant at speed on mountain roads.

Now at over 8,000km the engine is a whole lot smoother and is probably at full performance. City fuel consumption is now around 5.5lhk and the ScanGauge is nicely calibrated. Filled up this morning when the Scangauge indicated 17.5l used and an indicated 5.8lhk (40.6 US mpg). The pump clicked off at 17.5l. Spot on. The ScanGauge is showing whopping fuel consumption at every stop for a red light. Auto shift has reprogrammed itself and it will now hold 70kmh in 5th and the shifts are much smoother... I strongly suspect that the dry clutch plate needs to bedded in over time.

My feelings are that fuel consumption and comments about jerky auto shift on a smart before it's done at least 5,000 miles are probably premature. Some cars may be built a little "looser" and smoother; dunno. Mine was a little tight. It has not burnt a drop of oil... but it stinks of rich exhaust when cold started and that is when heaviest fuel consumption can be seen on the ScanGauge.

Cairns City Council recently bought a few smarts. They are the 2009 Aussie pulse with mhd. Ignorant critics cited "Experts at Top Gear Australia" as saying it was a bad choice of vehicle.... I happened to see two young ladies trying to park one of the Council smarts this week. I stopped and chatted when they had finished trying to fit the car into a space big enough for an SUV... 3ft off the kerb and 5ft behind the car in front. The driver was not too happy with the smart; the passenger seemed to love it. They had been told to only use the auto shift... and were finding it jerky... and if they get poor fuel economy the critics will start up again. Of course I told them to ignore the clowns at Top Gear after their "smart hearse" skit.

I use the paddle shift in preference to auto program when I need control over the car. It gets to be really embarrasing when I use auto from a standing start at a red light and the smart screams off and redlines at 60kph in first and sticks there with the turbo spun up... it just refuses to upshift until it has time to decide that I dont't want to go faster. Fun but foolish... flick the paddle to convince it to calm down.

I've dropped from using Shell V-Power down to Shell 95. No loss of performance or fuel economy. 95 is the recomended fuel and it seems that higher octanes do not give any benefit. Lower octane or ethanol mixes I will not use unless smart approve them... which they don't for our models.

The next thing after becoming a smart fan is to become a ScanGauge addict.

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Permalink Reply by mr bad example on June 13, 2009 at 1:56am

dittos to the scan gauge addiction! LOL

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Permalink Reply by mr bad example on June 13, 2009 at 1:50am

i just logged a trip up to wisconsin dells, for the summer smart meet, over 100 smarts in attendance (no 450's though) 203 miles and 54.5MPG, not too shabby! take that MR EPA 41HWY MPG!!!! driving 200+ miles and showing 5/8ths of a tank, with a sub 9 gallon tank is pretty satisfying!

i think the turbo does make the smart a little more thirsty, welcome back ian! there are a few people in the states making aftermarket turbos for USA consumption, the HP nearly doubles, i wonder if the clutch would hold up?....

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Permalink Reply by Ian Pellant on June 13, 2009 at 5:13am

yep... I'd worry about the clutch fitted to the US 71bhp model getting a bit stressed if turboed over 100 bhp. The Brabus Extreme pushes over the 100bhp mark... but it's modded to take the loads. My 84bhp turbo is rated the same fuel economy as the 71bhp cabrio in "extra-urban" and "combined" figures, which are a little thirstier than the 71bhp coupe. Kinda hard to figure that since the tests are rolling road with fudged air resistance... as can be seen in the 84bhp turbo figures being the same in coupe and cabrio. The lowest figure we get quoted is 4.0 lhk (US 58.8 mpg) for the 71bhp coupe... you've got another 4.3 mpg to find yet! LOL

My pulse turbo is listed as 4.1 lhk (57.4 mpg) in "extra-urban cycle". I doubt I'll ever see that. Too much wind, coarse bitumen, hills and trucks on narrow roads to contend with.

The published figures are a bit artificial. Anyone who believes that they are readily achievable in real road conditions, needs to contact Mythbusters.

I may do a long trip this week and I'm wondering if I'll see better than 5.0 lhk (47 mpg).

All my driving is with air con on. It's winter here... in the tropics that has meant 17C in the mornings. With the climate control set on 22, it was actually blowing warmed air for a while this morning.

Cheers, Ian

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Permalink Reply by DendoRacing on June 13, 2009 at 8:12am

I have been averaging a consistent 5.9l/100km around town for the past 2000km which is better than the official 6.1l/100km. However, I don't do much peak hour driving.

Highway trips get down around the 4.4-4.6 range depending on which direction the wind is blowing. I reckon the aircon is worth about an extra 0.5-1.0l/100km depending on the outside temp.

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Permalink Reply by Ian Pellant on June 13, 2009 at 7:27pm

Peak hour (or up here, anyhour) driving with stop lights really kills the economy... certainly makes the mhd a good idea. Traffic lights a few hundred metres apart which all turn red as I approach, really guzzles fuel... watching the ScanGauge show a 5.5 lhk climb to 20 lhk stuck at a stop light shows how inept traffic controls can cause more loss to national fuel economy than the politicians, motoring journos or Greens have taken note of... too complex an issue for their binary thinking.

4.4 to 4.6 lhk is pretty good. I often see an average of the low 4s on the few straight, flat, sections of road at 60kph... then the next intersection or roundabout kills it.

I don't have any long, straight stretches at 100kph to monitor fuel consumption with air con on and off. Your guestimate of about 1 lhk is probably about it... that's why I'm doubtful I'll ever sustain a sub 5lhk up here... just too hot and humid to go far without the air on.

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Permalink Reply by Raymond E. Martin on June 27, 2009 at 2:46pm

I have an '09 cabriolet with 3600 miles. I have about 84 miles every day on US freeways marked between 65 and 75 mph. Around 70 I've seen between 30 and 40 mph depending on top up/down, windows open/closed, A/C on/off. Best milage is windows closed, top up. A/C off. 75 mph can drop it another 3-6 mpg. Slowing down to 55/60 mph gets numbers well above 40 mpg and near 55 mpg with the top down. I've also found that the level of the car matters when putting gas in. With the front end high the gas gage went berserk one day. Drive from South Bend, Indiana to Columbus, Ohio (where dealer is) didn't look too promising for warranty service, until the next 2 tanks proved ok ( with font end lower than rear). I seem to get a fairly steady 36-38 mpg driving around 70 going to work with outside temps in 80-90 F range.

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Permalink Reply by Ian Pellant on June 27, 2009 at 11:59pm

Hi Raymond,
A couple of questions:
What's the noise and wind like driving the cab at speed on the highway? (My only "cabriolet" was a Jeep Wrangler... it wasn't too bad until it rained and the water whipped around onto the rear of the windshield - a graphic display of airlfow.)
How much nose up causes the fuel gauge problem? It could be overfill that swamped the evaporator (?)

The variability in fuel consumption still has me baffled in my environment. It seems to vary from day to day doing the same trip, driving the same way, much the same temperatures. I'm wondering if vapour pressure (plus or minus) in the tank is a factor... would depend on fill and temperature and the gas cap venting?

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Permalink Reply by Greg Ballantyne on June 29, 2009 at 10:31pm

Well, now that the weather has been warm long enough to know.... I've moved up a little on the average mpg to 45. During colder weather I averaged 42 mpg. Not a large increase, but appears to be quite consistent. I'm wondering if those whose fuel economy varies, if they are getting topped up to the same level most of the time, or if the roads and miles traveled also vary. I believe the variation I see is due to that sort of thing. I doesn't take that much variation in topping off to make a noticeable mpg difference in an 8 gallon fill up....
But I'm consistent in the miles and roads driven weekly, along with gas stations used. That must be the main reason for the consistent measurement

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Permalink Reply by Ian Pellant on June 29, 2009 at 10:46pm

Yes... top up levels and pump used will cause large variations in mpg calculations.
Those of us using a ScanGauge that has been calibrated, don't have that particular set of variables.. instead I see when a pump is not delivering accurately. I use one service station a lot. One of their pumps gives me almost exactly what the ScanGauge registers for the total tank used. Another ot their pumps reads higher... so I avoid using that one!

Using a pump refill and calculating the fuel used is not a very good guide unless you use the same pump every time and fill to first click off every time.

The Scangauge is set to show trip fuel used. That way I can monitor the fuel used on each trip and can compare town to highway consumptions quite accurately.

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