Christy,
The ones with the coil wire uses resistance wire rather than carbon disks. They get warm to hot too. I've refurbed several of them by cleaning all the contacts and carefully tightening the rivits that hold the wires together (don't want to break the ceramic piece). I've even had to reattach some of the wires to make them work. "Generally" on the wire types if the swing lever is making proper contact with all the contact points and they are all clean, it won't get too hot. However, if all the wires are blue it's cos they got reallly hot. I'm thinking they loose their resistance then and just get hot.
The electronic ones I have had experience with were Singer factory units and one from Sew-Classic.
Joe