running hot right after starting engine

Check your rad cap rating, make sure it's right for the system. For every pound of pressure over the boiling point of 212º, the coolant will be raised 3º. A 15psi cap will raise the coolant temp. 45º.

Check for air in the system which can cause hot spots. Bubbles in the coolant might mean a busted head gasket. Any white smoke in the exhaust? Check only when it's not real hot, otherwise you'll be wearing boiling coolant.

If the thermostat was stuck open, it wouldn't be able to warm up properly. There's a warm-up period when coolant goes through the bypass hose in the water pump to circulate coolant in the block. The thermostat only begins to open once things get to operating temp.

If the thermostat was stuck closed, it would overheat, but not right away. Feel the hoses (don't burn yerself) to see if coolant is flowing through it. If the upper hose is cold when the engine is at or near operating temp., the thermostat is stuck closed.