I drove for approximately 2 hrs back and forth to seattle(like I always do)and this time my temps we're pegged fully towards the HOT end.My coolant was full.Oil was good.EGT's we're normal.No smoke coming out of the engine or anything.THe only thing was that when I shut the car off,all the coolant overflowed and spilled all over the deck.The coolant reservoir seemed over full but I'm sure it wasn't a couple of days ago.Could it very well be the thermostat?If not how do you think should I troubleshoot this?Thanks.

Best guess would be the thermostat most likely stuck closes or partially open. How hot was the radiator? The hoses? Let the car warm up, and feel the radiator hoses, they should get warm after 5 min or so..If after a while, they don't get hot, most likely the thermostat. Maybe a water pump going bad, but usually you will know when that happens...

It's your thermostat change it. If you can get your thermostat at kragen auto parts they have a life time one for a good price.
Don't forget the gasket part #5278086 $2 at a chrysler dealer.

Thanks.But...

UPDATE:
Well I didn't get a chance to take the thermostat apart cause nobody has the o-ring/seal in stock.I drove it for awhile and it didn't get to the boiling point.After about 30 min of runni'n around the temp gauge would go all the way HOT for about a second or two and comes down as soon as I let go of the gas.It did this for awhile.Yesterday when I shut the motor off the anti freeze overflowed.When I looked at it this morning it was empty.I filled it to about the right amount.Drove around and when I popped the hood open it was over filled again.HHHMMM.ANy good guesses?Someone told me it might not be the thermostat but more of the heat/temp sending unit next to it.Is there such a thing?Thanks guys.

It's your thermostat same thing happen to me. Press on the gas and the temp would go up then come down after a second or two. I put in a new thermostat and fixed the problem. As for the gasket no one will have it. I had to go to a chrysler dealer to get one.

UPDATE :

Well,I changed the thermostat.Seemed like it was fixed.But I drove to seattle again(bout two hours)and right when I was about o get home,on my way back,The temp gauge soared to HOT.I let go of the gas and it goes down.It never went up after that.I left it on idle and it never got hot again.The coolant reservoir was overflowing again too.What else should I check?

try a coolant flush. if that's not it then it's time for a water pump. may as well do a timing belt if your goin under the knife for the water pump

well...you shouldnt have necessarily refilled your coolant resevoir becuase just because there was no coolant in there doesnt mean that you didnt have any at all. It was probably all stuck in the engine. But i would rather have it overflow then overheat so you are doing the right thing by refilling it everytime just incase you dont have any coolant.

well,I think it's not the water pump cause I just rebuilt this bad boy 4000 miles ago w/ a new water pump.Is there any method of checking if the waterpump works?I filled the reservoir up yesterday and it was bone dry again this afternoon.hhhmmm..

see if the drain plug on your radiator is leaking, and that all the clamps around the radiator hoses are tight and sealing properly.

good luck