I have a 2003 Volvo S40 with just over 100,000 on the odo. Mileage has dropped to less than 20 mpg. Closer to 15 mpg. Runs very well, but "ouch" on the mileage.
As cars get older, the MPG decreases to a degree. Several factors contribute to maintaining MPG - what type of octane are you using? Has the MAF (Mass Air Flow) Sensor been checked? What type of air filter/is it clean? Type of spark plugs/coil packs? If you are at 100K, you are due for a tune-up, including a timing belt/water pump...so, $1K may be what you spend if you don't do the work yourself. Also, check your suspension (control arms, links, etc.). And don't forget tire pressure...if you are a mechanic, sorry if I told you things you already know...I'm learning the easy and the hard way about these things after 2 years of owning Volvos ('00 S40 and '00 S70).
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