Check the coolant level, drive belt tension, and temperature gauge to diagnose cooling system problems. If the engine takes too long to warm up, replace the thermostat. If the engine overheats, feel the upper radiator hose, if not hot, replace the thermostat. Never run an engine without a thermostat since it damages computers, emissions, and fuel economy. Assessing the upper radiator hose temperature aids in confirming whether or not a thermostat is open. Disconnect the battery cables before removing the air cleaner duct and draining the cooling system. Also, locate and disconnect electrical connectors at the thermostat housing, remove a hose from it, take out a housing cover and see how the thermostat is positioned.