gas mileage problems went from 28mpg to 15mpg

I just recently developed a problem with my heat cutting in and out on me, well i checked into the problem and my neighboor came over and we discussed it

went to autozone and got a new thermostat, everything works fine now. My Question is would the bad thermostat cause bad gas mileage?

no.. a bad thermostat will cause overheating.. or over cooling. What kind of carberator are you running? And have you checked for vacume leaks?
Mike

i remember when i added after market gauges.. like temp gauge n oil n volts.. my truck did the same thing... it was flooding its self.

If you truck runs too cool like if you took the thermostat out or it sticks open then the truck will burn more gas until you get to the motor's desired operating temp.
So yes a bad thermostat over-cooling will cause you to loose mpg.
I had this happen on my mazda and my roomates civic.

same thing with my GF's formula her dad put a lower temp thermostat and i runs way too cold now and burn alot more gas