I have a kicker ZX.850.4 and I'm running 8ea polk audio 6.5" 4ohm speakers. It plays at normal volume, but when i crank it up the amp goes into protection mode. Brand new amp. Brand new speakers. What can it be? Are speakers a true 4ohm? If not, is it possible that the speakers are dropping the amp below 2ohms?

Sounds like they are either
1) wired to the wrong ohms
2) amp is under powered
3) power and ground wire to small
4) ground wire not grounded well

what model are the polks? i know they have some components that are only 3ohm which is fine until your run more in parallel.

if possible i would unhook 4 of the speakers & just run the amp in normal 4ch mode. if the problem still occurs when you crank it up its probably the amp wiring (assuming since amp is new). if everything is fine, then more than likely the speakers are putting a load greater than 2 ohms.

Kyboy is right

The other thing I would do is out a Volt meter on the power an make sure the voltage is above 12v when you turn the volume up

These are all the right answers. If I had to guess, I would look at the Ohms for your speaker load and how you have them wired. If you are running it at 2 ohms or less, your amp is overloading and tripping into protection mode.

Overheating

Overheating is generally caused by the same issues I listed above. I run 6 speakers and 2 subs off 2 amps inside a compartment with no vents and black carpet and they have never ever overheated. I sometimes prop the door open to the little compartment just to make myself feel good. But overheating is generally caused by overpowering and amp by overworking it. I run all my amps at 25-40% and nothing more. If I was building a show boat I would blow them all the way out but I am looking for longevity.

1) wired to the wrong ohms maybe
2) amp is under powered how is an amp under powered?
3) power and ground wire to small it has a huge freakin wire abt 3/4"..lol sorry dont know gage
4) ground wire not grounded well dont think so bc sometimes it will jam then just cut off. its cut off while sitting on the trailer

here are the speakers i have

http://www.sonicelectronix.com/item_...o+MM651UM.html

the amp gets hot but not hot enough that you cant keep your hand on it. It has also cuts out within 2min of playing. sometimes it will rock for 2min and sometimes for 2 hours. when it cuts out i lower the volume and it comes right back on..

Amp is underpowered for the speaker set up is what that means. That sounds like your issue since turning it down fixes it. Check to see how you have the speakers wired and give us details of the amp