[srh]

ok, so I recently took my 2006 mazda 6 2.3 I-4 in for an oil change at a supposedly decent garage. The same day, while driving on the freeway, the car started sputtering (loss of power) with big blue clouds of smoke out of my exhaust. Took it back to the garage where they checked and apologized for overfilling my oil by 1 qt.

After they adjusted the oil level, the stuttering and smoke is gone but I'm suffering from severly lower gas mileage (~30%). I don't see any (black/blue) smoke from the rear, no oil leaking underneath and nothing funny or smelly under the hood. Checked my air filter which was fairly clean, at least no signs of oil there. Also, checked the oil level before and after a freeway test drive and didnt see any change on the dipstick.

Any ideas what could be causing my poor gas mileage? I have always followed the maintenance schedule and my car was in good condition prior to the oil overfill.

 

[MrTea]

is your mileage calculation w/ the time frame in which you were driving with it overfilled, or is it a full tank afterwards already? As you can imagine oil doesn't combust all too well in our cars, so while it was overfilled and burning oil this would hurt mpg a bit.

there really is no reason it would effect mpg after the issue was resolved, so some clarification would be needed.

 

[srh]

thanks for quick reply but no, the low mileage is occuring also after the oil level was fixed. I just took a test drive on the freeway and I can almost see the guage drop. Also, normally my fuel guage hits the half-way mark at about 250 miles, now I'm already way past that but have driven only 210 miles. Next weekend I have to go out of town so I'll fill up fresh and use that as a good test drive to guage my fuel usage.

Is it possible my spark plugs are oil-coated or something like that? But if they don't fire I would expect to see black smoke from my exhaust.

 

[MonoxideChild]

possibly with all the smoke out the exhaust. it clogged up your cat. which would effect your gas mileage.

 

[MrTea]

if your plugs don't fire you should be able to feel it, and if it's consistent you might even get a CEL for the misfire. you have a 4banger, it takes all of 5 minutes to check your plugs....won't hurt to check them as they could be a bit dirty.