1994 merc topaz

PROLEM 1: my brothers 1994 merc topaz started acting weird the other day. the fan quit working so i rewired it to work. we took off the thermostat because it would over heat. know it will sit at a red light, get hot then when you take off it will cool down abit then it will get hot. any suggestion why the temp gets hot then goes back down for a bit and start getting hot again? maybe a sensor? PROBLEM 2: when he turns the ehater on, it blows smoke in the cab and smells like raidiator fluid.

Stop driving your car NOW before you warp you freaking heads and do more damage. Now you most likely heated up your rad so much that you cracked something *same thing happened in my girlfriends toyota.* When you are sititng at a stop light your engine is heating up cause there is no Airflow. When you start to move again air is flowing over the Radiotor and engine cooling it down slightly. Why your heater is blowing smoke is probably because you cracked your heater core too and it is letting burning hot Radiator fluid into the heater system. Really what you need now is a new Rad but if you keep driving you will mess more things up.