My amp (Phoenix Gold QX-2180) cuts itself off after an hour of having it cranked to the nuts. I'm thinking of installing a little fan on it, because no matter how windy I make it in the truck, or how high the AC is turned on, it still happens from time to time. The amp is mounted properly BTW, lots of space between it and the box, vents are aimed vertically, air passes around it nicely. I think it's just getting tired (had it for 4 years now).