Declining fuel mileage

[NonyaBisness]

tires can definitely have an impact but you would notice it on the very next tank after you put them on if that was it, I would definitely lean toward the spark plugs at that mileage and like others have said there is a 5-10% drop in fuel economy during the winter mix season which starts around september/october (at least around here it does), I can always figure out when it happens because i'll lose several miles to a gallon from 1 tank to the next.

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[latole]

Change plugs is a must over 100K miles. It might be the issue of low milleage
Replace main belt too

 

[BrandonSmith]

I replaced plugs at 100k and it did not affect mpg. Ymmv

 

[latole]

I replaced plugs at 100k and it did not affect mpg. Ymmv

Normal, best to replace before than after.
About main belt ?

 

[BrandonSmith]

Normal, best to replace before than after.
About main belt ?

No I haven’t replaced the accessory (serpentine) belt. There’s no visible wear on this original belt, so no need to replace.

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