hi and first thread here.

purchased my '11 fit sport 5 speed few months ago. have enjoyed 34+ MPGs up until about a few weeks ago. now i cna barely break 30 MPGs and thats on the hwy.


preface:

i always drive to end of the tank.

i can fit 11.4 gallons every time i fill up by topping off completely.

with that 11.4 gallons driving to the end i can squeeze out 369-374 miles to the tank with combined hwy and city driving. NORMALLY.


now i can barely hit 343 miles on that same 11.4 gallons

i have checked my tire pressure and all 4 tires are at 35 PSI

i try to keep the revs at 3k and no more even on the hwy. at the most i will get to about 80 mph in some stints..


im at about 3/4 of a tank right now and it shows 27.6 MPGs and even on the hwy for 30 min and the MPG indicator at or above the 53 MPG mark it still takes for ever to go from 27.6 to 27.7.

the only thing i can think of is that i have about 4500 miles on the car now and it says oil at 60%, is it possible that the oil is affecting my miles per gallon?


i am reading all over the place on here that people are going up to a year on the same oil just topping off and reaching 14-17k miles on one oil change but none of those people once mentioned a decrease in miles per gallon.


whats going on here? is it because im using the AC constantly? i just see the AC compressor really dragging the engine down from 34+ MPGs to 25+ MPGs unless its a combination of AC always on, 90+ degrees in these hot days and decreased oil viscosity.

 

I'm no MPG expert, but I wouldn't rely on the trip computer to calculate the MPG. I would try to manually compute the MPG and see if it differs any from the computer.
How often do you go 80 MPH? That will definitely decrease your MPG's vs. if you went 65......Also, was your AC on all the time when you were getting 34+ MPG? Combine the AC being on all the time with 80 MPH speeds and you will definitely see a drop in MPG......not sure about the oil hypothesis though.

 

yes i always used the AC from the day i purchased the car which is why i was so happy i could use the AC on and still get 34+ mpgs in this car.


if i calculate then that would mean i got 343 miles on my last tank and i filled up to 11.2 gallons.

that equates to 30.625 MPGs

what i really want is 36 MPGs x 11.4 gallons = 410.4 miles.



im thinking before i go on my trip to destin im going to change the oil right before the trip see if there is a noticible different in efficiency.

 

It's a combination of A/C use and summer fuel with ethanol.

Unscientifically, I've watched my mpg drop 10% in the past few weeks driving Metro Atlanta. My winter average is around 34, then it went up to 37 in April, now it's around 32. It could be slight changes in driving behavior, but this is my 2nd spring with the Fit and I noticed the same thing last year.

MPG seems to peak here in the spring when for a serendipitous few weeks the cool weather (no A/C) and switch between blends seems to favor us. I have a theory that between winter and summer blends we get a few good weeks of undoctored gas. Then we get hit with the double dose of ethanol and A/C. Even if you use the A/C all the time, the compressor runs less with cooler outside temperatures.

I don't think the Fit is any more prone to this than other cars, but we're more aware of it, especially with the mpg display.

Lower viscosity oil helps get higher MPG (that's why car manufacturers are recommending it). I wouldn't change it.

 

What grade gas do you use?

The Honda fit has a 10.6 gal. tank. I'm not sure how you are filling up with that much gas. When the nozzle clicks you should have 10 gal. and its not good to top it off.

It will take a long time for the mpg to go up on the highway if you have been doing mostly city driving. I have never dropped below 26 when doing all city driving. If I were to go from say a half a tank city and get on the highway it would take a considerable amount of time to get back up to 30 mpg on the read out. What you could try to do is a reset on the highway and see what you get and do the same with city. This should give you a good reading of what mpgs you can expect in the two scenarios. when doing equal driving between city and highway 30 mpgs is roughly what you should show on the reading, at least for me. when the fit is in idle it will drastically lower the reading. Also running the a/c on full blast seems to make a decrease. I have never shown better than 35 and that's highway with a reset, but I am mostly around 30 with equal driving city/highway.

 

i use 87 octane gas, i traded in my 04 330i bmw that i was using premium gas so one of the reasons to get the fit was using 87 octane. (yes i know i could use 87 in teh bmw and i have before but the gas mileage was even worse with 87 octane)


from what you described though sounds like what im experiencing. it takes a long time when i do a lot of city driving so i will try the reset onthe hwy and see how im running to get a better feel of that.


i know the tank only holds 10.5 gallons but if i top off carefully i can get 11.4 gallons in and the gas is RIGHT at the hole and then i put the cap on. i guess the fillter neck from the gas tank holds a considerable amount.


i dont spill any gas so i fill up with as much as i can.

 

I can say one thing..the Fit hates city driving....by this I mean I get horrible MPG's when I just drive around the neighborhood to do errands and stuff....and by horrible I mean 23-24 MPG {at least that's what the trip computer is telling me}. I live in a neighborhood with lots of stop signs and traffic lights, so that is the main problem. Even if I drive 5 miles to the market, because of so many stop lights, MPG stink. However, I get great gas mileage on the highway/freeway. I can do mid-upper 30's easy. I usually avg right around 30-32 mixed. I just think the city MPG's for a car that is super light weight and that only has 117 HP would be much better....I only have about 800 miles on mine, so maybe it will get better as the engines breaks in a little bit.

 

Why are you filling it up like this? The manual warns against topping off at all and you are topping of to the extreme. You may have damaged the vapor recovery system.

You have no real need for 400 mile tankfuls so what is the deal. I mean it's not like you are driving across the desert with no gas station in sight. Do you just hate going to the gas station? Is it an ego thing? Whatever it is think twice before doing it again. Read your manual and go online to read about the dangers involved in topping off.

 

That you know of. The fuel expands with heat after it leaves the in-ground storage tanks. It has to go somewhere.

Google "topping off gas tank."

 

Yeah, especially if you park it shortly after filling up. And the expansion issue becomes greater in warm weather.

 

Many people on the forum don't agree but 93 octane will give you more mpg a tank, your engine will run smoother and last longer. When you take into considerations the fact it only cost around $2.50 more to fill the tank it is worth it.

It is not good to top off your tank for several reasons. One is it can cause gas vapors to leach into the air and even rob you of the gas you think is going into your tank. The pumps are designed to suck gas back in. Also your tank needs that extra space for the vapor and can cause your vehicle to run poorly when topped resulting in lower mpg. I used to do this until I had several stalls in my f150 that I contribute to over filling.

 

Have you checked your air filter? Maybe its clogged up?

 

That might reduce power but wouldn't lower MPG. Fuel injection meters gasoline for the correct air/fuel mixture.

 

Ok guys, lets not get too side tracked here about my topping off habits. I understand what the manual says and will take that into consideration, I merely pointed that out to show that I do deposit 11.4 gallons into the fuel system overall and what I am getting and what my expectations are.


i've been driving since 1994 and out of the 25 hondas i have owned and numerous other vehicles and the several engine swaps, OBD system swaps, fuel system swaps i have installed along with removing purge canisters for fuel vapor relief in the tank... i have never once encountered any adverse effects in performance, fuel efficiency or failure of components.

the main reason they dont want you topping off is for the environment and EPA regulations and Ozone layer protection.

your gas caps have relief valves built into them and can relieve pressure so you do not have to worry about your tank exploding or incurring any damage from expanding vapor in the system. it your fuel system relieves pressure this way then it CAN be harmful for the environment however if vapor pressure is relieved the CORRECT way which is if gas is not above the filler line covering the vapor reliefe valve then those vapors are just recirculated back through your charcoal canister back into the tank for emission purposes.


either way no damge will occur.

 

OK, so screw the EPA and continue with your practice of filling the tank to the brim. Why do you feel a need to fill this way. Just curious? There has to be a reason

 

honestly i do it because its force of habit and i've always done it, it doesnt bother me.

i do a lot of driving and i just like stopping less for getting gas and every little bit helps for me.

 

Topping off is a good way to wear out your charcoal canister prematurely...some states check that for inspection.

I bet if you used 93 octane and stopped topping your tank you could go more miles than you do adding that 1 1/2 extra gallons of low grade. Try it out.

 

Well, you obviously wait till the last minute to fill. I guess stopping at the gas station must really be the last thing you want to do. Gas systems are changing. You might want to reconsider a habit you developed years ago in a modern car. Things do change. Ya never know. I get a good fill-up by setting the pump speed to it's lowest when I know it's within two gallons of being full. That way it fills higher before it clicks.

 

That was an unrealistic taunt, but you should try 93 and ten gallon fills to see if it improves your mpg, because if you are doing primarily highway miles you should be getting better mpgs than you are.They are two variables you can try to eliminate as the problem.

 

On the previous trips where you were getting good mileage were you using AC?

It's very possible AC just by itself is enough factor to knock down your MPG.