I recently noticed that I was getting about 1.

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?

3 Replies

DOCHAGERTY

MECHANIC
9,601 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

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

JEFFMILES

MEMBER
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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