Do you drain radiator to change thermostat on 2003 Chevy s10?

You don't *have* to drain the radiator completely to change the thermostat on a 2003 Chevy S10, but draining some coolant is highly recommended to minimize the mess and the amount of coolant spilled. The lower radiator hose is usually the easiest place to drain some coolant from, allowing you to lower the coolant level in the engine and radiator. You'll still get some coolant spillage, but significantly less than if you just tried to replace the thermostat with a full radiator. A drain pan is essential.