Today I went to reset my MI424WR today (because it hadn't been reset in a while and the firewall page had hundreds of UPnP entries) and accidently touched the coax adapter. Normally I wouldn't have even noticed, because as I recall, it never was even warm at all, but this time it was burning hot! Do I need a new router? (Also, this is a revision C.)
I am pretty sure that it should never be "noticeably hot" it always gets warm, it's electronics but definetely not "hot" it is well ventilated right?
as long as it's well ventilated then you may want to call in for a possible replacement, warm is ok, but never "hot"
I also have revision C, and today the entire router got so hot that I could barely touch it. Called Verizon, they said they're sending me a replacement (revision D) immediately. Apparently they have seen these types of overheating on a monthly basis. So, I would suggest you call up Verizon and request a replacement.
Probably good advice ... a general rule of thumb for any properly ventilated consumer grade electronic device is that it should NEVER be too hot to touch (well, unless it's purpose IS to get hot -- like a stove, iron, etc.). It may get warm or even feel hot, but not so hot as to be painful to touch. Even improperly ventilated devices shouldn't get that hot -- they all should have a thermal overload protection inside that will kill power to the electronics before a risk of fire develops (and to protect the electronics from frying themselves).