I recently noticed that I was getting about 1.

Tiny
ANONYMOUS
  • MEMBER
  • 2004 MAZDA 3
  • 80 MILES
I recently noticed that I was getting about 1 MPG less for mixed driving and so I figured it W's time for a tune-up. I had a faulty pcv valve replaced, new spark plugs, new coil connector, and oil change. Now, I get 2 MPG less on mixed driving and 5 MPG less on highway. I think the mechanics are honest, but I think they missed something. Can you give me some thoughts on what to have them check?
Thursday, October 25th, 2012 AT 2:20 AM

3 Replies

Tiny
DOCHAGERTY
  • MECHANIC
  • 9,603 POSTS
There does not seem to be a trust issue here, as far as with your chosen mechanic. I dont perceive any wrongdoing, and there may be factors not included in the words in your post. Most car manufacturers use adaptive systems and it may simply be a matter of allowing the car to adapt. 2 mpg difference by itself is not alarming. I would look at the additive and multiplicative fuel trim and see if it is at or near its limit. There are many factors to consider, lets take them one at a time, agreed?
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Thursday, October 25th, 2012 AT 3:54 AM
Tiny
WRENCHTECH
  • MECHANIC
  • 20,761 POSTS
I don't see your location but I suspect the weather is cooling off which will reduce the fuel mileage. Oxygen sensors get clogged and becomes less sensitive and accurate which will also effect your mileage.
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Thursday, October 25th, 2012 AT 9:57 AM
Tiny
JEFFMILES
  • MEMBER
  • 1 POST
I disagree. I think 5 mpg on the highway is significant. That said, I have a previous mechanic, and he supported your suggestion that their might be issues with my fuel. I disagreed until, my buddy suggested that different formulations with the cooler weather can create problems. I took his advice, and ran a can of Seafoam on a quarter tank of gas, and then, I've been running premium fuel from Exxon. I appear to be back to my previous mileage. As for the O2 sensor, I asked them that, but they said it checked out fine. Thanks, for the input.
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Friday, November 9th, 2012 AT 7:16 AM

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