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Reduced gas mileage

I have a 2001 Buick Century. I routinely got 270 miles/tank. Then the gas guage stopped working. That was ok because I could estimate the mileage by the tripometer. But when that went out, I had to have both fixed. Now I get 220. What would cause such a decrease in gas mileage?

Because you are talking in terms of ‘miles to empty’ rather than ‘miles per gallon’, the first thought that comes to mind is that:

  1. Could the new gas gauge be inaccurate, indicating empty before you are empty?
  2. Could they have done something when they replaced the sending unit (I presume) that is causing your tank to fail to fill all the way up? Did they have to drop the tank?

After that, it is the usual list of suspects: Weight in car, tire pressure, air filter, worn ignition or oxygen sensor, obstructed exhaust, malfunctioning A/C or power steering pump, driving patterns, neighbor kid stealing gas at night…

Try the old miles traveled divided by gallons used method then see how these figures compare to similar cars (I hesitate to say compare to EPA figures). Lets see what kind of mileage your getting before deciding there is a problem.