Amp issues

I currently am running 4 amps in my boat. All amps are working great but one, the kicker 600.4. It keeps shutting down and my other kicker 800.4 works great and my other 2 class d amps (alpine) are also running fine but the 600.4 keeps shutting down after 20 minutes of play and turns on and off while the rest of system is going strong. I thought maybe the batt's were low but the boat cranks right up and I am thinking maybe it's that they are too hot (not very good air circulation) but why aren't the other amps shutting down. This amp was transferred from my old boat and it worked great. Just wondering if it's time for a new amp?? Any ideas with the issues??

Heat would be my first guess.
Maybe the air circulation was better in your other boat.
Is the same speaker configuration applied to this amp?

Heat would be my first guess.
Maybe the air circulation was better in your other boat.
Is the same speaker configuration applied to this amp?
Same speaker set up except I replaced a set of 6x9's with a set of 6 1/2's and the amp that is running the 6's is cutting out. I thought it was the heat as well but why aren't the other amps failing.

I have multiple amps in my boat, and one kept cutting out. I didn't know if it was heat or low voltage. New batteries cured the problem, the amp was just going into protect mode due to low voltage. Why that amp and not the other, I don't know, it must just be more sensitive to the low voltage. The boat started without hesitation, so I didn't think the batteries were the problem.
How old are your batteries? If it is getting near the time to replace them anyway, I would just go ahead and get new one's, and see if it cures your problem. No real money lost if it's about time to buy new one's anyway. Mine were Optima, and I took them to a battery shop, and they load tested them, and said they were good, so don't trust the tests.

Just got the boat so the batteries should be o.k. but then again they are the cheap kind.

The first thing I would check for is some kind of short. Make sure all your speakers are good. Also check to make sure there are no pinches in any of the wiring. A small short would also cause this same problem.

Same speaker set up except I replaced a set of 6x9's with a set of 6 1/2's and the amp that is running the 6's is cutting out. I thought it was the heat as well but why aren't the other amps failing.
As long as the resistance is the same between the two pair of speakers, ie; the 6X9's were 4 ohm, the new 6.5's may be less.
Check installation. make sure the power and output connections are clean, well made and secure.
Next time out when the amp start's to cut, feel the amp wiht your hand, (if it's accessable) does it feel really hot? check the voltage at the input connections, is it below 11v?
Not sure about Kicker, but in my experience most amps thermal protection is around 140 degrees, and have a low voltage threshold of around 10.5v.
Or, it could be that the amp is done. :)

There is no access to the amps so I can't feel the temps but this amp is smaller than the second kicker while it's pushing the same amount of speakers so maybe the amp is working harder than the 800.4. There is no air circulation as to where the amps are located just the internal fans the amps have. Wired for sound installed the amps and they say it could be just the heat make it cut out and they will install and access panel with a mesh screen with fan to help out with the air flow