It is possible the motor is not killed yet. As mentioned if the oil is frothy and an off-white mix instead of oil, you're done. Likewise you can get a head gasket, head, or block to leak from the water jacket to the cylinder so it wouldn't necessarily show up in the oil. It will show up if you fill up with water, leave the radiator cap off and run the motor. Bubbles coming back means compression is pushing into the coolant. If a head was cracked in an intake runner you won't see that, but sweet smelling exhaust, a wet spark plug that smells sweet may indicate your coolant is going into the cylinder with the odd looking or smelling plug.
That is just damage assessment though.
Right now you have zero coolant flow. Your temp gauge is not faulty, it means the water at the top of your motor is that hot. Your radiator is probably cool and your heater core is obviously dead cold because there is no water moving through them. Check the return hose to the radiator(top hose), if it is not pressurized and hot the thermostat is not opening. If it is hot and the lower hose or lower area of the radiator is cool then the radiator is plugged. This assumes you have a working water pump. Look for evidence of leakage at the pump, that the pulley is actually spinning. Also is the fan pulley driven or electric? Make sure it is working although with an inop fan your heater core would be hot as hell assuming everything else worked.
So first, get coolant flow in your engine, then run it to assess damge. You'd be suprised how long some cracked heads can go, especially with careful application of Bar's leak. I suspect the radiator. Did this vehicle ever sit inactive a lot? That plugs radiators quick. For expediency, remove the thermostat completely and replace the housing without one for now. Run the car. Does the temp act normal now? If so the thermostat was bad. If not it is most likely the radiator.
At this point if you run a garden hose into the radiator with the top hose removed water should gush out of the top hose coming from the motor. Put your hand over the top inlet to the radiator to force the water through the motor. If nothing is trying to come out of that top inlet to the radiator, there is your sign, that means no path between the fill cap and the inlet, also meaning no path between the inlet and the outlet where the motor picks up it's coolant. With the radiator and motor full of water and top hose still off, start the motor. Water should pump out. If so, your water pump works. Reconnect the hose, fill with water and dump in two jars of Naval Jelly from the auto parts store. Run for 30 minutes if you can without overheating, if it gets hot, shut off and let cool, then repeat. After 30min. run, pull the top hose and repeat garden hose flush. All manner of *expletive deleted*it should come out. Do this treatment a couple more times working up to a little driving. When the temp acts normal replace water with proper coolant.
FYI, Naval Jelly is phosphoric acid and sold as a rust remover. Does wonders on all the oxide scale in an aluminum core radiator too. Not sure on terminology or your level of comfort with all things automotive but when you say thermometer I assume you mean sending unit and temp gage. The thermostat is a mechanical bi-metallic spring check valve that regulates water temp. It stays closed to help the engine get up to temp then the hot coolant opens it and fluid flow through the radiator commences to cool the motor. If it never opens you get no cooling and a cold heater core. A heater core can also be plugged but the rest of the cooling system should still function so if you have that problem it is not your primary one. Get a Haynes manual, this can be easy to fix yourself.
