Hi,
Coils come in two varieties, normal(12v) and resisted(8v), and if you put a resisted coil designed to run on 8 volts behind a ceramic resistor into a normal system with no resistor then the coil will get very hot and melt the plastic follower on the contacts, or just get the coil hot if you have an electric ignition/contactless points.
Also check if one or more of the leads to the coil or plugs and rubbing on the back of the grill as this can cause misfirring but not the over heating coil.
Terry