[dmjlambert]

That is possible, but likely it would have been a 12V solenoid on a 1956 car. I think you would have to measure the current it is drawing with an ammeter and calculate how many watts of heat it is dissipating.

I don't know if it is practical to determine if the device can actually get rid of the heat continuously and not burn up or melt. You would need to see the published specifications for it to really know what's going on, and you may have trouble finding that. And if you were to drop the voltage sent to it, it would affect the strength of the push it gives to the throttle.

If it were my engine and truck, I would re-evaluate the situation and probably not use it. There are probably current day and more efficient solenoids you could use that won't put such a hot device that close to your fuel system. Are you having problems with the idle speed or just wanting to make use of the solenoid?