Recently, my gas mileage has seen a drop off and I can't seem to figure out what the problem could potentially be. For the past 3 or 4 tanks of gas I have only been able to make it about 370-385 miles before I have to fill up again. A couple things have changed on my car in the past month:

New tires along with alignment: Yokohama S.Drives (stock size) all w/PSI of about 35
New air filter: changed from paper to K&N

I had the oil changed (July 1st - about 2000 miles ago) also at my local Acura dealership. The original tires I bought the car with were Sumitomo HTR+ stock size. I have always filled the car up with BP Ultimate 93 octane and nothing else. I have always gotten 400-425 miles between fill-ups because I drive some around town and some on the highway. Nothing has changed about my driving style either.

So please help!!!!! What is going on and why has my gas mileage dropped???

 

I will be interested to see the results of this. I'm hoping to get 350 out of my current (first tank) of who knows what the dealer put in there. maybe the computer is overcompensating for the new free flowing air filter? i read somewhere that the oil is thicker right when its changed....that wouldnt impact gas mileage enough to notice

 

To me this doesn't sound all that bad -- actually it makes me worry. I drive only around time and average only 23MPG according to the computer. Is this low? I don't drive agressively at all.

 

Well I don't think it's too low. I just know that I had been average 25-27 mpgs and it just seems to have dropped off. I'm not too aggressive either...I cruise on the interstate at 5 over the speed limit and usually around town at 5 to 10 over.

I've thought about the computer having to compensate for more air flow. I've also thought about switching back to a paper filter but I want to give the K&N a chance for a little longer because supposedly I should get better gas mileage with it. I spent $65 on it so I need to give it a chance before I give up.

Another thing I've thought about is air conditioning. I've ran the a/c a lot so this might have something to do with it.

 

One of your calipers might be slightly sticking/seized. Check the trans fluid level as well, the alignment may have been done impropery, and the tires may have more rolling resistance than the others. I think the main culprit is the heat, and using the A/C more often.

 

Hmm... heavier tires and used AC a lot..

 

Have you changed where you are purchasing your gas or has the place you buy your gas started adding ethanol? It is not uncommon that up to 10% ethanol is added and this will cause your performance to suffer a bit.

 

Change back to synthetic oil

 

I haven't changed places but all of the gas stations in my area are adding up to 10% ethanol now like you said. They've been adding ethanol since mid spring but I didn't notice the drop off til mid July.

 

These were my guesses as well. If you ended up toed out, that would hurt your mileage. Everything else you mentioned I would assume would help the mileage so this is a strange situatuon indeed.

 

I run the ac almost constantly right now. I'm seeing about 28-30 mpg. I keep it set at 70 degrees.

The new tires could easily play a big roll in your MPG drop. if they're heavier and/or stickier than your previous tires this would cause your mpg to drop 1-2 MPG.

Ethanol will decrease your mileage. If you always get your gas from the same place, you might contact them to see when they switched to a mixed blend.

Did your MPG drop after the new tires/alignment or before?

the K&N filter won't hurt your mileage. I have one and it didn't affect it. may have actually helped on the highway. you may

if you're last oil change you switched from synthetic to regular oil, that will decrease your mileage. you didn't say if you changed the type of oil in it during your last change.

 

I think it's both the tires and air filter. When I bought my Civic Hybrid new in 03, it took about 3K miles for the tires to settle in and my MPG rose about 2-3. When I replaced them at around 45K, MPG dropped again for 1-2K miles, then went back up. Also, the tires could have more grip than stock. Also, that air filter could be allowing more air - engine is compensting with more gas.

So with the tires I'd be a bit patient - they may come around when you get some wear on them. Don't know what to tell you about the air filter, other than you can swap back to regular and see if it matters.

 

My tires are stickier than my last set. The last set was Sumitomo HTR+ which are high performance all-season tires. I bought 4 new tires and replaced the Sumitomos with Yokohama S.Drives which are Ultra High Performance Summer tires. I only have about 1k miles on them right now so I will continue to watch and see what goes on.

I honestly do not believe it is the alignment because I think I would have noticed it by now. The alignment and tire change was performed by a reputable shop who has the best technology available. My car doesn't pull to either side and is driving as straight as an arrow. It's also smooth with no wobble so I believe the tires were balanced correctly.

As far as oil goes I have always had it changed at a Acura or Honda dealer and both use Honda Synthetic Oil.

Thanks for all of the input and suggestions. I've considered everything that's been suggested.

 

double check to make sure the K&N filter is seals against the airbox. I had an air leak in mine (I have the Icebox) and my mileage dropped by about 2mpg until I sealed it up correctly.

 

I lost about 2 MPG the minute I got the S.Drives put on. That was the only change and it dropped right away.

 

I drove with a K&N filter (cost less than $65, WTH did you buy yours...), switched back to paper mid-spring over concern of the K&N letting more dirt in, didn't see a change in MPG. A/c generally won't impact MPG more than 1 MPG (according to Consumer Reports), but I run mine at 72 or 74 degrees depending on the day, and how often I'm getting in and out. Keeping it at 68 or 70 in the Carolinas during the brunt of summer like i did last year, you are probably seeing a MPG impact on city driving.

I don't trust the MID for the MPG measurement, btw. I've seen it vary from 0.8 to 4 mpg difference from what my miles/gas ratio shows. (Though I sometimes suspect a gas pump of being inaccurate.) I would suggest you keep a log of your mileage (fueleconomy.gov has a handy spreadsheet you can download), you can can even post it online and compare with others (6-8 of us at fueleconomy.gov[1]).

[1] Correction, now there's more of us. https://www.fueleconomy.gov/mpg/MPG....cura&model=TSX

 

+1 ... it is very tricky getting that air breather box to seal on the K&N filter.

 

you're getting 380 miles per fill up?? Wow... And im so happy when I get 320 miles, I mostly get 280 miles..

 

I have seen this talked about in the forums before.

Its your tires - Yokohama S.Drives are famous for having extremely high rolling resistance. I have seen complaints on the Tirerack reviews about gas mileage dropping significantly (20 percent drop is possible).

This phenomenon wasn't really seen until the last couple years, when tread design advanced significantly. Now they make tires specifically for Hybrids that have ultra-low rolling resistance (my point is that the industry knows about this).

 

Same. 320 is a good tank for me with my driving style and amount of stop-n-go traffic I get stuck in.