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I recently replaced head gasket, brand new head, mas air flow censor, injectors, air cleaner, serpentine belt, air-conditioning compressor and cleaned alot out of the motor old carbon out of the throttle body and cylinders. My question is why after doing all of this am I not getting better gas milage. I bought this car recently, I only put 200 miles on it before the head went. Before replacing the head I had the trip set to check milage. About 3/4 of the way throught the tank of gas the head went. So anyway after checking it on the first tank I got 25.8 mpg. After doing all the work to it and the second tank of gas I'm only getting 23.7 mpg. To me it doesn't make sense.

 
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Is this city or highway driving?

 
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city driving

 
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Not a statistically significant difference.
City driving has alot of variables. Maybe there was more traffic, maybe you had more red lights, maybe it was hotter outside, etc, etc.