So my gas mileage indicator was telling me I was getting 37-38 miles per gallon for about a year. I am not saying I believe that, but a couple months a ago it started slowly but steadily and continuously going down. Now I am at 32 mpg and still decreasing. That is a huge change - even if the original was overestimating I am getting lower and lower mpg by the same calcluations of the same indicator

I checked the tire pressure, I do everything I am supposed to do (I think) like oil changes and air filter etc.

My driving habits haven't changed at all.

If it is just something wrong the the mpg indicator, I don't really care, but if there is something wrong with the car, I would like to know

2009 Honda fit sport about 30,000 miles on it- no mods.

I don't know anything about cars . My local honda dealers are terrible, so if I can avoid them I would prefer it.

I have always had great advice on this forum and everyone is so nice, so I hope that maybe someone can help me

Thanks in advance

 

Have you ever used a calculator to double check the mpg when your meter was showing upper 30's? Also have you switched gas or filling stations? Has the weather gotten colder recently? Use a calculator next time and double check your mpg meter!

 

We have had some cold days recently but that can't be the reason because the mpg has been steadily declining over several months.

I can do a check with gas and math, but I don't understand why the mpg gage would behave like that.

If it is under or overcalculating (there are already threads on overcalcuation) it does that in a stable way (i.e. it also tells me I am getting about 37 mpg for 1 yr). Why it would start getting lower and lower over a several month period is very odd.

 

My best guess is its the colder weather, I'm in VA and its been cooler here for the past few months also letting the car warm up in the morning before heading out can hurt the fuel mileage! I'm getting around 33 mpg and that's letting the car warm up before driving in the morning.

 

Exactly what is happening with mine. Great mpg up until just recently. All systems in tip-top condition. The only explanation, I think, is something with the gasoline. Winter blend in Cali, or some such. I've changed brands, and still the decreased mgp.

 

These results are "hand calculated" by Excel and show that MPG vary according to the seasons here in Pennsylvania. As for the Dash MPG versus the "hand calc'd" results, yes, individual fill-ups sometimes show a +/- 4 MPG difference but when considering the +/- over 35,000+ miles, there are only decimal points difference, at least in my case.


Again, colder weather, which has occurred more intensely and for longer durations on the east coast this winter than previous years, affects MPG. Gasoline blends are different in winter versus summer, the fuel / air mix is different for a longer period of time as the engine comes up to temp in winter and you may tend to idle it longer to warm it up before going. Not sure how much this matters but my car "feels" more sluggish starting out when below 25 deg F and that "drag" may hurt MPG a little too.


Best thing to do is view the Dash MPG as an "estimate" and get your calculator out to divide miles by gallons to get to the true MPG.


You can see from my graph, I was playing around with different weight synthetic oil, which in the end didn't make a difference but season of the year is the big driver of MPG.



ccc

 

sudden loss?


check tire air pressure. read sidewall for max, if 40psi, run 30-35

check for vacuum leaks. Listen for hissing or such noises under hood.

Go for a drive around a parking lot or city block. Then hop out and feel wheel rim and see if hot. If hot, carefully figure out hot hot brake caliper is, and if hot, brakes are dragging.

Did you recently have a shop change your oil? check and see if they didnt accidentally damage the undertray splashguard and simply removed it without telling you. That panel is worth a good amount of aerodynamics under the car

 

+1

I always lose 1.5 - 2 mpg during the winter months. I'm around 33-34 now. When the weather warms up it's 35-36.

 

If using the defrost, your air conditioner comes on, sucking some mpg. I think I loose about 4mpg at least in winter.

 

thats a great idea but I don't warm up the car. Most is a minute or less

 

Interesting - is that also true of the heat or only the defrost?

 

The car has it's own warm-up cycle to lower emissions. Excess fuel is burned the first few minutes to heat up the catalytic converter whether you sit in the driveway or drive it (better to drive it).

I noticed this month when it sat in 20F all day outside. The idle speed was increased, transmission gear selection stayed in a lower gear longer, all so the engine could burn fuel and warm up. It remained in this operation mode until I had driven about 2 miles, even after the blue "cold" idiot light went out.

 

My title was wrong - it isn't really sudden, more like "recent" and only if you count a couple months as recents. Before oct I was getting 37-38 and it started to decline in oct and has been slowly but steadily going down till Jan where I am now at 32.

I will check all those things
Last oil change was after the decline (about Nov)

 

Only defog/defrost, and at colder outside ambient temps, just when you have it on recirculate to dry the humid warm inside air, otherwise the compressor shuts off quickly.

 

Thanks ! very useful to know

 

It's the cold weather and normal wear and tear on the car. Had my car for 8 years now and cold weather has consistently decreased my mpg to 31-34 while in the summer I get 35-39.

 

thanks for all the help - it is the cold and/or the defrost. Had a warmer day, no defrost and mileage is going up a little, so there is no problem with the car. Thanks for all your help ! Saved me worry and some $$$ as the mechanic

 

13fit has a good point about tire pressure. Without getting into the Gas Laws (Charles and Boyle's), an internet search identified a rule of thumb. Said that most places in the USA experience a 50 deg F drop from summer temps to winter temps and that reduces tire pressure by 5 psi, which is enough to effect handling and gas mileage.


So, winter temps represent a multi-prong attach on your gas mileage. Although you can adjust the tire pressure back up to normal, gas blends, high idle, and warm-up times in order to effectively defrost the windshield can't be helped.


Hawaii would probably have the least variation between summer / winter temps and gas mileage should be more consistent.