[rotorwrench]

An ignition system in good condition won't get all that hot while the engine is running. When the engine is not running, with ignition switch on and points closed, the coil becomes an electromagnet and will get hot. An ignition system with a bad condenser and a failing set of breaker points will not be dissipating the electromagnetic energy very well so it will get hot under those conditions but it will also be running like crap. If a coil has a damaged winding, it can have a higher than normal resistance and get very hot. The old coil testers from back in the day had a warm up cycle to get them up to operating temperature before the test would begin. It would let the technician know pretty quick if it was a good functioning coil or not.

While I can agree that a 1.5 ohm coil will dissipate heat better having an external ballast resistor just for the fact that is is external to the coil, I don't think it makes it any better than a 3 ohm coil that has epoxy insulation. They are made to take the heat that they normally dissipate since it is an inductor and not a resistor. Like I mentioned before, any coil in an ignition system that is working properly should not get all that hot. They should be touchable for several seconds without scorching your hand. The ignition system only build the magnetic field for a split second before it makes each induction cycle or spark. This is so rapid that it shouldn't get all that hot.

While some manufacturers may use oil for an insulator in coils of older design, most old originals had bitumen or what is commonly referred to as tar. Tar is basically a solid unless it gets very hot. It will liquify at higher than normal temperatures but this is telling a person that something is wrong with it. Many old coils were designed to be upside down in order for the high tension lead to fit properly. Model As all had coils with the terminal pointing down.