What is the hottest thermostat you can run in the 5.7L for better mileage? Has anyone tried this?

Isn't the stock thermostat 203?

I'm not sure. I put a185 in a few years ago and was thinking off going the opposite way now. Trying to get more mpg out of it if it's possible.

Changing the 'stat isn't going to affect mileage enough to warrant even that tiny expense. However, running the engine past its design limits can certainly affect your wallet.

So in your opinion what stat temp would you run?

I used a 180 for a while, but I went back to the 203 (not enough heat in the winter).

yup----stay stock, thats what its designed for

Wait a minute Mike, I live 500 miles north of you and a 180 works here very well year round, so are you really in north Florida or somewhere else?

I run a 170 here and get plenty of heat during the winter.