Rep Power: 150

01 LX Sedan, 159K miles...
I have filled her up 5 times since I purchased. The following MPGs are based on dividing miles driven by the fuel used to fill up.
1. 30.91
2. 33.26
3. 34.35
4. 34.96
5. 37.35
I drive the interstate for 10 miles during my 28 mile circuit to work and back. I haven't changed my route since I began driving the Civic.
I'm glad I'm seeing great numbers but I am skeptical to trust them. It just can't keep going up, so time will tell me the true MPG. Any ideas?
I haven't tuned up the engine, changed any ignition parts. I did get 4 new tires (14in Michelin all seasons) between fill ups 2-3.

 
Rep Power: 518

Let all the air out of the tires and the gas mileage should go back down.







Tires could have something to do with it.
Summer fuel blend could have a lot to do with it.
Fuel quality has a lot to do with it. (TopTierGas.com)
Summer weather could have a lot to do with it.
HOW you fill the tank has a lot to do with it.

Just keep tracking mileage with every fill up.
5 tanks isn't much to get a good average from IMO.

 
Rep Power: 313

Summer gas blend Good for 3 mpg or more.

 
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I fill up at the Costco in Norfolk, VA. Costco is a top tier fuel seller. I set the pump on 2nd notch until it shuts itself off. I don't top off or round up. Do all regions use summer and winter blends? Here is the southeast tip of Virginia, we get mild winters...
But that would explain it... I've lived here my whole life and never seen a mpg increase like this with any car in the past... if it was a gas blend, wouldn't it have been noticeable in other vehicles too?
I think the tires are part of it for sure. I had filled the old tires to 30 psi.
I changed oil and filter, drained and filled 5MT, both with Honda fluids. Maybe the Honda fluids are liquid gold?
Very pleased with the mpg of a 13 year old Civic! This is winning!

 
Rep Power: 518

Is Costco on the Top Tier list?
(Looks like it is.)


You do AFAIK. It's nationwide.

I think the switchover to summer blends has to be completed by June 1st, so it's probably been in use for at least a couple weeks already.
Only to conscious (and conscientious) drivers.

 
Rep Power: 150

well thanks, that sounds like a very reasonable reason for the increase in mpg that I've been seeing.
BTW, nice rims on your Civic Ezone!

 
Rep Power: 518

Thanks. They came from an 11-12 Accord coupe V-6.


My gas mileage dropped like a rock after putting those on.

 
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Funny, I've been wondering about the mileage I'm getting on my '01 LX Coupe, must be the same thing. I failed to reset the trip odometer on the first two fuel ups, but the third one I managed 389.x miles on the tank, and then the next one I hit 413.x. Every time I fill back up it takes a bit over 11 gallons, so I'm not actually emptying the tank even though the light comes on. This last time I filled up with Shell since it was the cheapest close by place. First 2 fills were Wal-Mart/Murphy USA fills, 3rd was HEB, neither of which are listed as top tier, but who knows who they actually get their fuel from without seeing the bill of lading.

All I know is like OP, I'm happy with the nice mileage.

Edit: It's also worth mentioning that I don't subscribe to the "how you pump it" idea (not saying it's wrong), I always pump full speed. That said, I also tend to take my time and wash my windows or something, occasionally resetting the handle to top off; so I may end up with the same results as someone who pumps slower. Sometimes I'm able to pump another dollar or more into the tank this way, sometimes not even a dollar.

 
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I find a blend of fuel octanes helps mpg a bit, if not outright performance.

 
Rep Power: 367

winter impact, yes.

this is my 95 miata MPG... clearly the winters are no good for it.

 
Rep Power: 518

The idea is to repeat the same filling pattern each time so you have a consistent fill amount in the tank each time you fill it up.

What I meant by "how you pump" was like if someone let the nozzle click off and pull it out on one fill, then on the next fill try to keep clicking another $2, or keep going until it's full to the top of the neck. That gives an inconsistent 'full' amount in the tank, and leads to erroneous gas mileage calculations.......
And a saturated charcoal canister, and possible false EVAP codes.

The tanks are designed to leave an air space at the top to allow for fuel expansion and to minimize raw fuel getting into the canister. If someone keeps clicking the fill nozzle to get that next dollar in, it takes away from that space.

 
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Lots of other factors as well. Is there an incline at the pump you fill at, that puts the opposite corner of the tank higher than the filler side? With my Escort I could get ~3 gals more into the tank after the first trip at the pump handle, if I rocked the trunk slightly. THREE GALLONS... no perceptible effect on evap, either... just a 'git-'er-done' tank design.

Air space for expansion, in a 12-gal tank, is most likely minimal as far as design. I worked with 5-gal tanks right above hot, 120-hp/liter engines and their exhausts -- if anything, they'd design even more air overhead for crawling in traffic due to more exposure to heat... but they don't. Just make sure the expansion valves (evap in a car) are clear and not kinked or blocked, and you won't encounter any problems filling up.

Won't go into the myriad other factors that affect perceived mpg, too many to type. My method isn't anywhere near scientific, but when the low-fuel light comes on solid is a consistent fuel level to start with. Go to the same pump at the same time of day. Can't exclude that someone got 92 before you, and you're filling a gallon of with his/her leftovers in the hose, when you're expecting 87. But enough records over time will show data at least close to accurate.

 
Rep Power: 256

new oil would also have an impact especially if the previous oil was of heavier weight. many people opt to use 5w30 or more instead of the recommended 5w20 i believe honda also allows 0w20

 
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I don't know what weight oil the previous owner used. After the first tank of gas I changed it with Honda 5-20. The kid at the counter said 0-20 was recommended too.
I live in the coastal flat lands. I bought the car at the end of April. The weather has been very consistent. Its just now getting hot. I expect running the AC will take a toll on my mileage.
I think the last figure, 37.3 is probably incorrect, most likely the pump clicked off before it was completely full.
I doubt the winter blend of fuel was in the pumps at the end of April, and if we throw out the first and last figures, the mileage increase is nominal.

 
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Another factor in that graph however, is that in order to keep fuel mixture close to stoichiometric, the MAF FI system in the NB's BP motor will add fuel to the mixture to compensate for higher air density due to low temps. So really it wouldn't matter if the ethanol content changed or not... you'd still use more fuel to drive around, esp if the temps dip into the 50 degF range or below.

 
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See, that makes sense. What i was getting at is all the folks I've heard claiming you should always pump at the first or second notch only. I liken that to folks who still try to claim burning a CD/DVD at the lowest speed will produce a more reliable burn.

Pump however you want, just be consistent seems perfectly reliable to me.

 
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Oh forgot to add... the median trend for that graph shows gentle, consistent dips and rises into worse and better fuel economy. Since summer and winter fuel blends aren't added gradually but rather abruptly switch over... the change is again more likely to be from ambient temps due to seasonal variation, than ethanol.

 
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although i step less on gas pedal in the winters, so i guess it could be much worse

 
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Yup. Gotta remember too that even if the coolant warms quickly on the gauge due to a good thermostat and healthy cooling system... your oil, trans fluid, bearings and seals will still have extra viscosity and shrunken sizes, until they warm. All of that is add'l load compared to summer...

My uncle (who owned and serviced all of the eight cars in his family, including four CVCC Civics *shudder*) said that he taught my cousins to make their cars last by driving <25 mph in the first five mins of driving, esp in winter. Heard this repeated decades later with NPR's Car Talk (Tom & Ray Magliozzi, 'Click' and 'Clack'. Makes sense to me.