Sudden Gas MPG Decrease
 

I have about 3000 miles on my TSX and I have been averaging about 350 miles a tank before the low fuel light comes on and when I fill up it takes about 13 gallons. So I am averaging about 27-28 miles per gallon. Well this is great for half city and half interstate driving. The last couple weeks I am only getting about 270 miles per 13 gallons. My MPG has dropped from 27-28 MPG to 20-21 MPG. I only use 93 Octane. The car has an automatic transmission and everything feels fine, driving and noise wise at least to my knowledge. I am taken the car in next week. Does anyone have any idea why my gas mileage has decreased so much? Thanks for your help. :dunno:

how many times have you gotten 20-21? that is very low, even when pushing my car really hard i dont drop much below 24.

Do you have a CEL? If you do, get it checked and repaired, you're warrantied all the way, no worries.

Since my first tank of gas I have kept up with how many miles I go per tank and how many gallons it takes to fill up. I am on my 3rd tank of 93-octane gas that I am getting 20-21 MPG. Right now I have 70 miles on my trip odometer and the gas gauge is about 30% from full (full being 100%). I have check for gas leaks and I do not see anything on the driveway after parking over night. Thanks for your help.

No I have no lights coming on. I am taking my car in next week (earliest they could see me). But I just wanted some ideas of why it could be doing this. Might help when I take the car in and talk to the dealer next week.

i wouldnt go by the gauge (% left) i would go with the odometer and gal filled...i assume that is how you also do it.

Yeah I do cause looking at the gas gauge now just pisses me off cause I feel like I can watch it move LOL. :swear:

maybe its the weather? but still that's a big decrease

i have the same problem except my average miles per tank is like 250-260, and ill be honest, occassionally i drive relatively hard... but when i dont i still get the same mileage.. i should prolly take it in huh?

Did you use air conditioner constantly?

i do use the a/c a good amount. but it usually around 76 and with around 2 or 3 bars. i dont blast it very often. but when everyone is saying theyre getting twice as much gas mileage as me, its gotta be more than the a/c, no?

Yeah I use my AC too leave it on Auto at 70-75. I live in South Carolina and the temps in the summer are in the high 80's - low 90's.

yeah, sunny south florida is soo hot. today it was 97F out, not to mention the humidity. though now with my mind on the gas mileage i set it at 78 with four bars, and then 3 and then 2 and then 1 as it got more comfortable to lower. still, i just filled up and ill be driving good and sacrificing some a/c to see if its me or the car..

very interesting thread here.
if you like racing and reving your TSX, of course there will be less mpg, true in any car

fuel
 

your car is still relatively new at 3000miles and most mechanics will tell you that mileage will not be consistant. Hi octane fuel is denser and usually gets more mileage.

Do you fill up at the same service station all the time? Not sure about where you are, but in Australia we have some problems with some outlets messing with fuel additives , water in the fuel and general bad quality fuel. Filling up on hot days is also affected by evaporation apparantly too.

Someone correct me if I am wrong, buy doesnt the AC compressor run all the time when it's hot outside regardless if you have the inside temp set or 75 or 65? I don't think it cycles on and off.

No I dont fill up at the same station all the time. But the ones I do feel up are usually the best in our area. I always use 93 Octane.

sorry for ressurecting such an old thread, but better than making a new one right?

well anyways, ive noticed a decrease in the number of miles i get on a full tank. i used to get about 340 miles on a tank (city and highway) but now i barely seem to make 300. is there anything that could cause this sudden decrease?

i am at about 5,500 miles, and i experienced this drop around 5,000 miles.

any ideas?

Could be because of the weather and your car's A/C being on for a longer duration.

actually, my driving style is exactly the same. and i usually drive only at night and i never turn on the AC.
i dont understand. do you think it could be b/c i switched from 76 gas to chevron? i heard 76 gas has best mileage. any truth?

Not sure about 76 and chevron as we don't get that here in Australia.

When is your next service due?

Could be lots of things. 40 miles delta is a 12% drop, so not drastic. I believe I've seen differences in gas similar to that. The Non-oxygenated premium fuel usually gives me an extra 1 or 2 mpg over ethanol premium. Could be low tire pressure, oil condition/level, or air filter (though not likely at 5k miles).

Are you sure the routes have been similar (city and highway mix the same as before)? I get great highway mileage (33+) but can really lower it quick with even moderate stop and go driving.

Go back to 76 and see if you get the miles back. Summer mix gas mix generally improves fuel miles. Are you sure Chevron gas you got is not E90? That would lower miles.

The person from Australia - higher octane fuel DOES NOT improve mpg.

check you tire pressure maybe? it shouldnt make that big of a difference in mpg but it might help

That's a really significant drop, more than I've seen for any one issue. So it may be a combination of things. Some things to consider that hurt FE (Fuel Economy) that may sneak up on you:

- Excessive cold will hurt FE < 40 degrees usually
- Excessive heat forces running the A/C
-- for you, the question is were you running the A/C during the good FE time, or has the weather recently got hot - about the time your FE dropped?
- Tire pressure low
- Did you get the oil changed at 3K? Did they use the right kind?
- Did your station switch to a 10% ethanol gas? This lowers FE by 2-4 MPG.
- Change your route? Drive more agressively? Drive Faster?
- Any reason to belive the alignment is off?

That's about all I can think of short of something major.

I know this is a really old thread but I've kind of been experiencing the same thing.


Usually on the freeway I'd get about 33mpg when I'd drive 300 miles back home (going 75mph on cruise control), which would be about 520 miles a tank. I just recently got an oil change and now my gas mileage has dropped considerably... it's really frustrating. I noticed the drastic drop in MPG on the shorter trips I've been taking but I drove home a few days ago and it's considerably worse.

According to my gas gauge, navi trip computer and gallon gauge in the diagnostic screen I'm only getting 400 miles a tank :whyme: . I took it really easy on the way here and there weren't any environmental factors that would make that much of a difference. Going from 33mpg to 26??


My tire pressure is fine, and I don't think "winter gas" wouldn't make THAT much of a difference. The only thing I can think of is that when I got an oil change last month they used the wrong kind of oil since I didn't go to my usual place. I dunno whats up :whyme: :ugh:





edit: my trip computer average mpg seems to be pretty off as well too, and it used to be right about correct.

on my old civic, i noticed after getting an oil change, my gas mileage drops 1-2mpg. i think its because the oil is thicker when new.

from my experience, cruise control waste more gas. it uses gas when it is not necessary. i can net 30 mpg @ 80+ mph with 3 other passengers. just be smart with the throttle and youll save a lot of gas. very little pressure on gas when cruising down hill or flat. let it roll every now and then

I am getting 300 miles to a tank, mostly city driving.
08 TSX with about 3600 miles

I know ethanol has lower FE, but 2-4 mpg is a 10-ish percent drop.

E10 fuel should lower fuel economy by about 3% (Ethanol has 34% less energy content than gas), unless the TSX engine is especially adverse to it.

I probably should have mentioned when I measured that I was driving a Civic Hybrid, averaging about 45 MPG. It was an easy 2-3 MPG drop, so I suppose for a TSX it may be more like 1-2. Just what I observed...

I wish I could help you. Although this thread is older than both of my kids, I'm compelled to ask another similar question. I have a 2005 TL which I purchased new. I take care of it, thus it runs as well as the day I bought it, which makes it tough to justify another car payment. The car turned 130k today, and my mileage is roughly 17, almost all short city trips. But I've made the same commute to work for years, always getting 21mpg. Had new plugs installed, but is there a tune up procedure that might help?