Its normal for the Solenoid to get very hot. Don't worry about it.
if the outer casing temperature more than 50 celsius or 120 fahrenheit, the coil is even hotter, I think you should worry about it.
most of the solenoids are around 60 celsius or 150 fahrenheit upper operational temperature tolerance(the valve coil temperature), and even in our co2 system this temp pushing too far because constantly on for 8+ hours a day everyday.
Ten years back some people used clippard block type solenoids and others solenoids to make their DIY pressurized co2 system, but this particular clippard solenoid failed easy and often, because it is 6 watts, same as other solenoids that are 6 watts or more, they are good solenoids but not for our co2 system.
The clippard company also produce miniature mouse solenoid, Ironically, it turned out really good, only 0.67watt, normally don't feel any heat when it is working and it is 1 billion official on/off cycle life. It was back in 2013, Neilshieh, one of the young forum members successfully talked to the Clippard and have them make the 15490-5, the 1/8 NPT ported single manifold. Now it is possible to use this mouse solenoids and the numatics/asco stainless steel miniature solenoids on the 15490-5 manifold in our DIY co2 pressurized system.
for safety reason, a fail solenoid may not cause too much trouble other than non-stopping flow of co2 injection, then gas your fish, and cost to get a replacement co2 system and co2 refill, may not be much but no one wants that to happen.