How could I lose 10 mpg in a week of BETTER driving?!
 

I bought a 2013 manual transmission adorable Fiat 500 on March 17th and am in LOVE with this tiny car! Her name is Sophia...as in Loren...after all, she's Italian. ;-)

Anyway, the car is rated at 31/40 but the salesman swore on his mother's grave that some of his customers were getting 45 mpg. I was totally excited when after my first 117 miles, I got 48.5 mpg! And that wasn't even with perfect driving...some heavy traffic. Since then, I've been extra diligent about throwing the car into neutral and coasting as much as possible, etc. I was expecting to get 50 mpg on this fill-up, but nooooo....I averaged only 38.2 mpg! How can that be?! I've done the same percentage of highway vs. city driving I think, or at least approximately. I've not been gunning the car or anything. I can't figure it out and am really upset. I would have kept my 35 mpg 2008 Scion xD and saved $10,000. Although I love this Fiat for other reasons....money is money.

Now Fiat recommends 91 octane gas but says you are safe as long as you used at least 87 octane. Being cheap as I am, I got mid grade 88 gas. Is it at all possible that I could lose 10 miles per gallon by not using premium gas? That sounds weird to me. I just can't figure out what else could have affected my mileage that dramatically.

Thank you,
Atheria

Tank-to-tank fill error; environmental changes; route changes.

Hmmm
 

My routes are basically the same. It's a little colder but not enough to lose 10 mpg. Tank to tank error? I made sure both times to stop filling the moment the handle popped instead of trying to shove in extra gas.

Get a few more tanks through there before getting too excited.

Check the tire pressure.

Does everything sound OK?

Ommm...peace...
 

I am panicking with the first 326 miles. :-)

GASOLINE -- the 91 octane was 100% pure gasoline while the 87-88 octane probably contains 10-15% ethanol, leaving only 85-90% pure gasoline, and that means lower ENERGY (BTU per volume) content, which manifests as reduced milage.

...also, one tank-full does not a "trend" make!

Ethanol
 

I didn't realize that 91 octane doesn't contain ethanol! I know that regular unleaded here has 10% ethanol so I'm assuming 88 octane has it too. Who buys that E85 I'd like to know? In answer to Frank's question, the engine sounds fine.

Thank you. I will use up this full tank and try 91 next time to test it.

Atheria

Your engine may have a knock sensor that is being triggered by the lower octane.

As an insight owner I see a 5mpg different between tier 1 and tier 3 fuel. At that it takes a hit in colder weather too. Much of the US has had colder weather, has you? The computer too maybe off, the Insight is 2mpg+ than actual. :eek:

Knock sensor?
 

If a knock sensor is being triggered, how can I tell? I've never even heard of a knock sensor.

Yes the temperature in Albuquerque went down the past week. It was only 17 degrees this a.m. but warmed up into the 50s.

A 5 mpg difference between premium and regular is sizable. It's worth noting.

My Scion xD's avg. mpg. sensor was about 2 off also. My new car is confusing and I am still trying to figure out all the gauges and buttons.

I don't know, I'm just guessing at this point.
38 on regular is a bit low IMO, so that is why I considered it.

Not all tank guns switch off at the exact same point, in my experience.
I stop when I see the fuel reaching the edge of the opening. That way I'm sure it's always filled to the same level.

I noticed relatively poor economy when I switched from 92 PON to 87 PON in my TSX. The after the second fill on 87, everything was back to normal.

The other theories as to your drop in mpg sound plausible too. Check the pump next time and see if premium contains ethanol, and what percent. Since ethanol only contains about 2/3 the energy of petroleum, that can make a big difference in fuel economy.

In Oregon, all fuel contains 10% ethanol, regardless of octane rating.

If the fiat is like the smarty and required preminum fuel then you should use it since its a new car that is something that could even void your warranty.

I go to sams club and get 93 octane for my insight. Its not required, but it gives a little boost in mpg and maked for much better perforformance in agressive driving. :thumbup:

My previous car, a Nissan Almera, was hard to fill to capacity on the level and would take over 2 gallons less when the side with the filler cap was slightly lower.
Used to park it on the wrong side when sloping towards the pump. Maybe this applies too to the 500?
Also cold weather, esp. cold starts, really ruin FE. If your commute is shortish that alone would explain the fallback.
Bet you will get 50+ mpg from that baby by summer :)

if Fiat themselves recommend premium fuel, use it.

anything with a functioning knock sensor can run on 87 octane fuel, but if the calibration and engine is setup for premium, you WILL see a drop in efficiency.

isn't that a turbo 1.4? use the premium. our pacifica recommends 89 and if we use 87 it drops 1-2 mpg.

i had to dig, but the non-turbo 1.4 has a cr of 10.8:1, turbo version is 9.8:1

anything over 10:1 needs at least mid grade, but if they recommend premium you should use it.

A knock sensor is a sensor that can sense if your engine does have bad combustion, and that can lead to harming your engine components. So if a knock sensor is triggered then it regulates the spark on the spark plugs trying to fix that bad combustion. Usualy it can lead to bad combustion because of lower octane fuels (the bigger the octane the less chance the engine will have a bad combustion). So that's the first thing.
The second thing you should know that on newer cars while driving, if you put the car in neutral and let it flow, it spends fuel because it needs to keep the engine running...but if you leave the car in a gear and just release the accelerator pedal and let it float the fuel consumption will be 0! Because the car uses the inertion to keep running (to understand to keep the car running a engine has to use fuel, to rotate the crankshaft then the gearbox and then the wheels...but as I said if you leave the car in gear and just release the accelerator pedal then this whole process is going backwards...then the wheel are rotating the gearbox and the crankshaft and the result is, no fuel is needed to keep the engine running). But as I said this system is only on newer cars, and your Sophia is one of them :)

And the weirdness continues...
 

So during this morning's 22-23 mile cold commute, after finally finding the current time avg mpg sensor, Sophia was getting up to 48! I ended up mostly in the 45-46 mpg range. My car has a mind of her own...but don't all women? ;-) What IS different between my Fiat Sophia and 08 Scion xD named Bob, is that with Bob the mpg sensor would jump to 99.9 if I coasted in gear, but if I do that with Sophia the RPMs stay up and the mpg doesn't improve. My mpg only goes up coasting in neutral. She is not a turbo, FYI.

I'm curious about my next fill up.

Thanks all!
Atheria

Odd. My Prizm has DFCO that works.
I tested for it by keeping the car in gear with my foot off the pedal and turning the ignition to accessory, I felt no difference in acceleration.
Your car may be cold or simply needing to be broken in.

What else to expect? Italian ladies has a temperament of their own!
But keep them tires aired up, use the right gasoline, and treat her kindly.

almost every GM vehicle since ~1985 has had DFCO....

can't speak for other manufacturers.

A new car requires a breakin period and at least 10 fillups to get any type of idea of what fuel economy to expect during the rest of the breakin period.

Next get a decent economy gauge and be patient, your tank to tank can vary a lot depending on how big the fill was, your driving conditions, speed distance and weather. Drive gentle but too fast (mph) and you FE drops, drive agressive and slow with lots of coasting and it may well go up. If you have lots of stops expect it to go down a lot.

So in other words nothing to worry about, a scangage or the like helps but a new car takes a while to settle in.

Cheers
Ryan

...yes, your Fiat has a built-in MPG display, but notice that you have NO way of calibrating its values, which is the major reason people here keep metioning that you should consider getting a separate fuel economy guage, such as ScanGaugeII™ or UltraGauge™ or similar.

These devices (like your Scion) will jump to 99.9 mpg when you coast, but ONLY *IF* the Fiat computer goes into Deceleration Fuel Cut-Off (DFCO) mode...which it might NOT be doing.

End of day today...
 

Well, if my avg. mpg sensor is accurate, by the end of today I was getting 44.9 mpg. I clearly gain mpg by coasting in neutral. It's odd how the RPMs don't drop at all when I take my foot off the gas in gear. I'm also going into the highest gear possible without making the engine struggle. I was in 5th gear today doing just 45 mph.

Thanks again, everyone!
Atheria

If I hold a gear without throttle, I slow down more than clutch in. DFCO occurs, but it's engine braking...

If I am not accelerating, I am rarely in gear clutch out.

-All of these points here make sense. I, personally, would not get worried until a few thousand miles. Things have to settle, and that will really show how it will be...pre modification.

Your engine is linked to the road when in gear, it can't drop in rpm without slipping the clutch.
The Fiat 500 should be 2,360–2,530 lb, you have 3300 in the garage profile for sophia.

You don't ask a lady her weight. ;-)
 

GVWR = 3,300 lbs. Doesn't that mean the car weighs that much? That is on her door.

I guess I should buy one of those ScanGauge thingys. :-)

Fiats come with software you can download onto your computer. You then plug a flash drive into the USB port in your car and transfer your driving information to your computer. The software will critique your driving to tell you what you are doing wrong regarding mileage, etc. I need to try that.

Atheria

No, it means max weight with load.

3,300 lbs.
 

Seriously?! Oh geeze....LOL

Does this sticker make me look fat?

Ha! Good one...

I found the instantaneous mpg sensor today and it goes to just -- when I take my foot off the gas, so maybe my Fiat does have that deceleration feature. That sensor makes you become obsessive though.

You have no idea. I have daily logs for almost 30,000 miles now.

...obsessively aware of what affects your MPG, and by how much! :eek:

Noooo! My Sophia Fiat!! :-(
 

A stupid SUV kicked up a rock in the lane next to me and it hit Sophia's windshield making a big chip! ARGH!! She's only a week and a half old! I'm so pissed! I've got to get this repaired fast as it's the type that will easily turn into a major crack.

:-(
Atheria

Not all MPGs are the same...
 

***warning, long boring math ahead***

***Short version for the tl;dr crowd (apologies to people who have already seen this in my last 239023094 posts, it's a pet peeve on mine) *** changes in MPG can be misleading. You dropping 10 MPG isn't the same increase of fuel consumption as someone going from 100 MPG to 90 MPG (smaller increase of fuel consumption as you) nor 20 MPG to 10 MPG (larger increase of fuel consumption as you)

***long version starts here***
Just to put things into perspective, because changes in MPG can be misleading, these are the MPG figures converted into gallons used per 100 miles (G/100M):

48.5 MPG = 2.06186 G/100M
38.2 MPG = 2.61780 G/100M

That change of 10.3 MPG was an increase of approx 0.556 gallons per 100 miles. If you traveled the same 117 miles at the same MPG, you consumed 3.06283 gallons on the 2nd tank and 2.41238 gallons on the 1st one, for only a difference of 0.65045 gallons (about $2.458 more in gas at $3.779 a gallon)

If we apply that 0.556 G/100M difference in fuel consumption to a different car:
22.50225(repeating) MPG = 4.444 G/100M
20.0 MPG = 5.0 G/100M

That is a difference of 0.556 as well. So you're 10 MPG drop is the same as someone else's 2.50225(repeating) drop in MPG. Same amount of increase in fuel consumption, just a difference in expression of distance traveled per set volume instead of volume of fuel consumed over a set distance.

At the other extreme, it would be like someone who got 100 MPG (1 G/100M) dropping to 64.26735 MPG (1.556 G/100M) because their fuel consumption also increased 0.556 gallons per 100 miles.

Moral of the story: Do not get so hung up on MPG changes because they are not comparable to each other. Your 10 MPG drop is someone else's 35.7326 MPG drop and a different person's 2.50225 MPG drop. All of them consumed the exact same amount of extra fuel per set distance.

Oh dear God...
 

I'm so lost! ;-)

Thank you for that rather thorough explanation!

What is odd comparing my Fiat to my old Scion is that the RPMs do not go down when I take my foot off the gas like my Scion's did.

Atheria (at a glass place getting my windshield repaired)

It is a manual, so if you leave it in gear the engine revs according to the speed you move.
If your Scion had an auto without lock-up or with disengage then of course the revs will go down if the load does too. If it has a CVT then sure the revs go down. Unless, like me, you give it so little that it cruises in its most extended position.

Yeah, what RedDevil said. You need the foot off the gas and the clutch engaged (pressed in) to effectively coast with manual transmission.

I think my post got lost so ill say it again, your engine has a compression ratio of 10.8:1 and it NEEDS premium fuel.