What would happen if I replaced the thermostat on the Cadillac 1995 sedan Seville s l s with a 180 degree ?

Put the proper heat range thermostat in , don't bother with a fail-safe or any of the cheap thermostats, a cooler thermostat will make you car burn more fuel , because the ECM will think the engine is not up to temperature yet and keep the fuel mixture too rich.Also your oil will stay cleaner when the engine is up to temperature and you will have less emisions.