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Car doesnt seem to be doing good on fuel at all. Just changed plugs but I'm getting 280-300 miles to 8-8.5 gallons of fuel. I would have thought to be doing a bit better?

Just put new ngk iridium plugs in. Car has 22k miles on it now.
 

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How fast do you drive? How much is stop and go? Are your tires aired up to where you want them? There are a lot of variables that affect mileage. Chumly
 

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I see you're in a 2013. My 2012 was doing 45mpg before 22k miles, but it isn't unheard of for these cars to have a seemingly very long "break-in". Well, let's go down the list of possibilities:

How was fuel economy before the plug change?

What's your driving style like? Are you only driving short distances or in a city?

Do you use Premium fuel?

You did mention that the car was a bit of a WIP, so hopefully it isn't drinking an unnecessary amount of fuel for the conditions.
 

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Car doesnt seem to be doing good on fuel at all. Just changed plugs but I'm getting 280-300 miles to 8-8.5 gallons of fuel. I would have thought to be doing a bit better?

Just put new ngk iridium plugs in. Car has 22k miles on it now.
If you haven't, change out the air filter.
 

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Just my 2 cents... You're getting better MPG than I am... Over 90% of the resistance at speeds 65MPH+ is from wind resistance. I typically cruise "with traffic" in So. Cal. which can be between 80 and the speed limiter on the tollroads (and this is in the slow lane). At speeds greater than 50MPH, keep your windows closed. You get a lot more drag with the windows even partially open than you'll get with A/C. Ir"idiot"ium plugs are for smog. Engine runs a lot smoother with more torque using non-projected nose race plugs. And, no pinging (most pinging you can't hear -- but you'll hear the valves bouncing -- a faint sound like pocket change rattling around in a can). Pinging + time = valve job. I use Brisk MR12S plugs gapped down to 18 thousanths. There may be other race plugs with compatible threads/reach, but I haven't searched other brands for years. As I remember, the Brisk plugs need a 14mm spark plug socket which is different from the socket size the stock plugs required. One of the first things I did with both my 451 Smarts was to remove the stock plugs and throw them in the trash... Below is a pic comparing a Brisk race plug (on the left) with a stock projected nose plug (on the right). And yes, despite appearances, the Denso XU22HDR9 is an Ir"idiot"ium plug (heavy duty, hence the large center electrode). Garbage...



 

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Guess that explains why our 2011 with copper NGK plugs was only averaging 40 mpg over the last 5 years or so.....:)
 

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You won't get 40MPG if you drive like I do (or, have to). I've been passed by gardeners in their mini pickup trucks while doing 80+. They merrily buzz past me -- weed whackers and rakes flapping in the wind. It seems that everyone has to get to where they're going ASAP now-a-days... Even the pizza delivery guys drive like it's LeMans on the surface streets... But, my position stands -- Ir"idiot"ium plugs are for smog. My first 451 has almost 100K miles on it and it had a SFR turbo on it for it's first 6 years (boosting to 1Bar). It kept up with traffic (out here) with the turbo and it's valves are still fine. Bore scoping it, the cylinder honing is now a little light in spots, but otherwise nothing out of the ordinary.
 

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Not that it matters, but that 40 mpg running average includes trips out West on Interstates running 80 mph all day in 90 degree heat, as well as putting around town in single digit winter temps here in Ohio. All on copper plugs. YMMV, of course. :)
 

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My '09 451 (pure coupe with 15" BRABUS wheel swap) averaged between 38 and 42 pretty much no matter how hard I did or didn't drive it. Up and down the grapevine in SoCal for years at one point, 5x's a week, and still averaged 42 highway with the car.
 

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Aerodynamically, there's no way a Smart Car can get 40MPG at 80MPH... My Scanguage tells me as much (and yes, I have checked it's averaged readings against the fuel pump gallons delivered). Maybe if you drafted a semi going down the highway, but then they don't cruise that fast. But, I noted that there's a marked increase in fuel efficiency if I slow down to 60 MPH, which might get me into that MPG ballpark (my Scangauge would read in the high 30's)... Unfortunately, that's too slow for traffic in my typical routes. Drivers are far too impatient and will ride your ass in the slow lane if you drive at 60...Upping the tire pressures didn't help the MPG's, but driving with the windows closed did. I'm lucky to get 30MPG at the cruising speeds out here normally aspirated (no turbo). On the tollroads, it's literally pedal to the metal -- right against the downshift switch -- the whole way... I might upshift into 5th to lower the revs a bit and save gas, but that's about it... And, that's sitting in the slow land being passed by practically everything -- Ford Transits, MBZ Sprinters, diesel pickup trucks, Daewoo's, you name it. The lowest MPGs I ever had was between 18 and 19 boosting to 1Bar when I had a SFR Stage III turbo installed. Even then, I could be right up against the speed limiter and still get passed by gardeners in their little mini pickup trucks -- rakes and week whackers flapping in the wind... Still, I really miss that turbo -- had to remove it for smog inspection when the car reached 6 years old... Alas, my "new" Smart 451 (got it with 42 miles on the clock) was registered by Car2Go San Diego back in 2015, so even "new" Kalifornia thinks it's a 3 years old car. I'm hesitant to install the turbo on it as I'd have to remove it in just a few years for a smog inspection.... In some states, engines under 1 liter are not subject to any inspections... Alas, Kalifornia isn't one of those states...
 

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HI GUYS
So what is the plug number so I know what to buy? NGK copper?
I'd love to get 40 MPG. My best so far is 30-35 without air. and I just changed to "idiot"plugs. with no better than what it had in it which was "idiot" as well. Hmmm, that's what I get for following other recommendations.
 

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My worst MPG.............

Was a fill up with stated 91 octane,from Sam's Club. It had a VERY HIGH percentage of ethanol. Only averaged 30 to 32
MPG for that tankfull. Went back to Shell 93 octane and 40+MPG..................
 

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BOY OH BOY You hit the nail on the head with Sams. Both of my cars show a much lower MPG with there gas. THANKS ALOT. A good lesson learned.
Ned C
 

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I usually get 40 -42 with Shell premium and 36-38 with Exxon premium. Regretably, my local Shell station is now a Walgreens so my lifetime (10+ years) mileage of 40.6 is dropping. It's been around 38 over the last 10 fill ups.
 

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Discussion Starter #19
Well I decided to change the brand of fuel I was buying and took the car on my very first road trip.

I drove 230 miles on 4.5 gallons of fuel.


So I'm going to guess the company I normally get my fuel from is just junk. Because i didnt change a thing on the car or drive any different than normal. 70-75 for the most part of the trip.
 

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Would agree that hwy + A/C = lower mileage. I did a run from Toronto to London Ont a couple of days ago and was averaging 120 kph with a couple of faster short bursts. Half a tank took me just under 300km or 186 miles at speed. Was cycling my A/C on and off as it was one of those muggy days where I needed to knock down the humidity but things would get too frigid.
 
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