You probably need to replace the gas tank sending unit.
When I start it I believe the reading is correct but when I start to drive it goes to a full tank
The gas sending units in buicks suck and when you replace it you'll lose the ring that holds it cause it's rusted and you'll have to self tap the new one in
Looking for a Used LeSabre in your area?
CarGurus has 6 nationwide LeSabre listings and the tools to find you a great deal.
Search Buick LeSabre Questions
Buick LeSabre Experts
Related Models For Sale