Big drop in FuelEcon

[Luna V 2.0]

Since I first got my car I've been getting 32 MPG. Which I've always thought was pretty good since I do mostly city driving and other than cutting the AC most of the time I don't do much else to boost the mpg.

Lately I've been getting 25 mpg (ouch!) and I haven't changed my driving habits at all, I still drive the same route to work. The only change is that I've gotten new tires, but my mpg was dropping before that anyway.

It's been a gradual change, and at first I thought it was just that maybe I was using the AC a bit more, but even then it's dropped too far in my opinion. When I got tints and I had the AC on all the time I was still getting at least 28 MPG.

Any ideas what could be wrong with the car? I have my "maintenance" done at Pep Boys so honestly as far as I know they probably do absolutely nothing on the car other than oil changes. So theres probably something that is wearing out and I wouldn't know.

And yes I know I should do my own maintenance but it's just so conveniant to drop it off during my lunch hour and picking it back up after work, now I'm paying the price.

Anyone got any ideas what can cause a 7 mpg drop? (and still dropping!)

[CTScott]

Maybe Pep Boys filled it with 20W-50 at your last oil change.

[Luna V 2.0]

Is the oil enough to cause such a big drop? I always assumed that the biggest drop you can get from the wrong oil or wrong tire pressure could be 1-2 mpg.

And I didn't mean to pick on Pep Boys, I just meant I don't do maintenance myself and I don't know what it is that they're checking. I could always ask them to check something specific. I just don't know what could cause such a BIG drop. To me 7 mpg is pretty big.

[CTScott]

I'm not sure just how big of an impact higher viscosity can have. I would check the oil level to make sure it's not over-filled, as that could also have an impact.

[supmet]

Have you checked your tire pressure? A "little more" A/C and low tire pressure could easily drop your mpg by 7 or more.

Have you checked the air filter?

Does the car run normally otherwise?

How many miles do you have on your car?

Other than that, slightly older car + higher friction tires + a little more A/C = ~7 mpg

[Kaotic Lazagna]

You mentioned you got new tires. Are they the same as the ones you replaced? If not, then they're probably heavier. When I bought new tires, I failed to look at the weight. Since they were heavier, I lost 2-3 mpg. Also, low(er) tire pressure can drop your gas mileage by 1-3 mpg as well.

[Yaris Hilton]

Low tire pressure might drop you by 4-5% or so.

[spookz]

Faulty O2 sensor or dirty MAF can cause dramatic drops in MPG.

[jambo101]

What mathematical formula do you use to obtain your MPG figures? and how often do you use it?

[Kal-El]

I can't think of anything that could bring a Yaris' MPG down to 25 unless most of your driving is in gridlock traffic idling.

The average owner gets 35-41 mpg.

[talnlnky]

lots of factors... how many miles on your car.

I once had a mazda that Jiffy lube didn't put the air box back together correctly when they couodn't figure out how to check the filter (that filter was a bitch)... basically, the airfilter got bypassed from that point on... Mass Airflow Sensor got dirty.... mpg's went down a bit... and I saw weird issues with shifting and highway speed driving... thought my transmission was going out.

too much oil, or wrong type
low tire pressure... if you were running higher than 32psi, they prolly dropped it back to 32
gunked up injectors due to prolonged used of cheap gas
Lots of A/C use
A dirty car can actually make a few %'s difference when driving at highway speeds compared to a clean wax'd car

the width and weight of your new tires could also be big

[ka0sx]

check your air filter?

[roadrunner]

Many good suggestions have been listed.
1) Have you tried coasting, to see if the car is rolling like it should, and there is not some drag?
2) How about driving on the highway for a nice long drive, w/o the AC, to see if you mileage gets much better.
Just a few thoughts.
Please keep us informed on what you have done.

[bronsin]

Have you changed gas....maybe to an off brand?

[RedRide]

Also consider that you fuel injectors might need cleaning.

By law, a minimum amount of injector clener must be added to gas but we all know how the oil companys follow laws. :wink:
Even if they do put the proper legal amount in, it still is not enough and suplimental injector cleaner should be added by the consumer ocasionally.

My personal favorate injector/fuel sys cleaner is "Seafoam".
I have been adding a can of it to my Celica's tank about every 5k miles and it keeps everthing clean. It now has over 85k miles.

[Luna V 2.0]

Ok, my tires seems to be fine, I haven't checked the weight of the tires as someone mentioned they might be different from the ones I had before. Is that information right on the tires? I can't seem to find it.

I've been driving without the AC recently just to see what happens, its still too soon to see because I recently filled up. I calculate my MPG when I do fill ups, how many miles I got divided by how much I put in to fill up (how much I used)

So far I think I'll have someone check the air filter and the injectors as some of you suggested, the main problem is I know nothing about cars so I have to trust others to do the work correctly. Eek. I'll see if theres some improvement soon.

[talnlnky]

Ok, my tires seems to be fine, I haven't checked the weight of the tires as someone mentioned they might be different from the ones I had before. Is that information right on the tires? I can't seem to find it.

I've been driving without the AC recently just to see what happens, its still too soon to see because I recently filled up. I calculate my MPG when I do fill ups, how many miles I got divided by how much I put in to fill up (how much I used)

So far I think I'll have someone check the air filter and the injectors as some of you suggested, the main problem is I know nothing about cars so I have to trust others to do the work correctly. Eek. I'll see if theres some improvement soon.

unless you have over 30,000 miles i wouldn't even worry about checking the injectors... realistically... anything less than 50,000 and they should be fine unless you only put the off brand gas in your tank. Just check the air filter... if its nasty, spend the $15 and put in a new one.