whiteazn

2009 civic lxs...
Been doing regular oil changes (when the indicator showed). Recently got the air filter replaced too

I have noticed this for the past year.. Went from 33 mpg to around 30. But then in the past couple weeks it has since dropped down to 27-28. I don't drive it hard and my driving habits haven't changed so not sure what is going on.

I am at 55k miles...tires have around 12k miles...

Anything i should be checking for? Seems abnormal to go from 33 mpg to 28ish

go-part

When was the last time the spark plugs were replaced?

ezone

Did the mileage drop start happening about the time you got the new tires? Tires themselves can make a huge difference in gas mileage.

You wouldn't believe how much gas mileage my '12 lost when I put 18s on it.

Tire pressure. I air tires higher than spec by about 10%.





Also, use Top Tier gasoline. http://www.toptiergas.com/

See what RFG or oxygenated fuels your area uses for summer. This can kill some gas mileage too.

Bad math kills gas mileage.

Kids.

Traffic. Any time the engine is running and you aren't moving, gas mileage is dropping. Also, drive-thru lines.

What's in the trunk?

Air conditioner use.

Wrong oil.

Check engine light on?

Gas mileage is 50% about the car, 50% about the driver. The car does not need sparkplugs replaced until 100,000 miles, and the maintenance minder will pop a code for it.

IF the car were to need plugs earlier than this, then that would mean there is another bigger problem IMO.

gothteach

I was having exactly the same issue. Went from about 31 mpg to 27 mpg immediately following installation of new tires. Just discovered that the installer had underinflated them. Filled them to the appropriate pressure this morning and felt an immediate difference in handling and ride. I still need to drive a couple hundred miles to see what the mileage is like, but I anticipate that is the solution. I had tried several other things like a fuel system cleaner, checking the air filter, and using higher grade of gasoline, all with absolutely no effect.

Good luck.

ezone

For anyone else that finds this, cold weather will cause tire pressures to drop.
Even with Nitrogen in the tires.

You can't defy the laws of Physics.

whiteazn

So, been a few years. Been keeping an eye out this whole time. And it's just gotten worse.

I am down to 25MPG for the past year or so. Could get worse depending on use (AC during hot summer, new tires, etc)

Recently, I have:
replaced spark plugs
verified tire pressure, and put more just because
Replaced Air Filter
Fuel Injector additive
Fuel injection system cleaning service
Got oil change at same time as injection cleaning
Using better gasoline + 91 Octane

Nothing in trunk (actually, not even the spare tire is in the trunk), slower driving overall

I even took a road trip, so all highway miles. Before, I could easily get 400 miles a tank and this was driving faster. Now, I am getting 300 before I need to fill and this is driving at a slower pace.

Nothing gives. I was debating on just replacing brand new fuel injectors. But at this point, highly doubt it going do anything. No check engine indicators. Outside of this issue, and a starter replacement, the car would be fine.

anyways. As much as I hate the car right now, still beats having a newer car with a car payment + higher expenses. ... for now

GolNat

iTrader: (7)

Dirty or bad O2 sensor?

I find I get worse MPG with high octane fuel. I have not tested this to great lengths though.

whiteazn

Don't they give off a check engine light when it goes bad?

Though, just looking at google, guess not. Was under assumption that it would. Will try that out soon and see how that goes

ezone

Usually, but not always. Depends on the sort of failure.
Sometimes the engineers couldn't predict every possible failure scenario.
Sure, try it. Primary is an A/F sensor.
Use the LOW octane gas, and get it from a Top Tier station . http://www.toptiergas.com/
Can you get straight pure gasoline in your area? (not ethanol/ethyl alcohol 5/10/15%) Alcohol blend fuels cause gas mileage to drop,. Just about everything in my area has 10%, and they want to increase that to 15%.


Valve clearance check and adjust?

What tires are on it? Got LRR type tires?

whiteazn

Yeah, according to that, both Chevron and Costco are top tier, which I have already been going to already and have been even before I even got the car. So didn't need to change anything there other than verify at the station. So don't think it's so much the gas itself.

I switched back to lower octane gas. I mainly did it right after the fuel system cleaning.

Don't have LRR specific tires. I did get new tires a few months ago, which caused an economy drop (as expected), but has gone back up since. (to 25-26ish). I forgot name of the new ones I got. But the prior ones were the Michelin Defenders

I'll be doing the O2 sensor replacement soon.

As far as valve clearance, haven't done that. Don't have the tools for it, but based on Google, I think I can try to do that.

ezone

Chevron already has Techron in it, which really is great stuff.