# Dramatic drop in gas mileage per gallon

**URL:** <https://community.cartalk.com/t/dramatic-drop-in-gas-mileage-per-gallon/22442>\
**Category:** Maintenance/Repairs\
**Created:** [November 23, 2008, 6:17pm UTC](https://community.cartalk.com/t/dramatic-drop-in-gas-mileage-per-gallon/22442 "2008-11-23T18:17:24Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![jpeters](https://avatars.discourse-cdn.com/v4/letter/j/da6949/32.png) [@jpeters](https://community.cartalk.com/u/jpeters)\
**Post date:** [November 23, 2008, 6:17pm UTC](https://community.cartalk.com/t/dramatic-drop-in-gas-mileage-per-gallon/22442/1 "2008-11-23T18:17:24Z")

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My 2003 Nissan Sentra used to get 35-38 mpg in freeway driving, and then rather suddenly it was only getting 25-27 mpg highway. Changed spark plugs and anything else mechanic could think of. Better for a few days and then back. I’d get 100 mile to quarter tank, now 100 to 1/3 to 1/2 tank.  
  
  
  
 On Car Talk I think I heard (ll-15-2008) that it might be the thermostat and/or something else but was driving and couldn’t write it down. Is that true and what is the something else that it could be? Are these expensive changes?