98 rmk 700 overheating

I just bought a 98 rmk 700 with 825 miles and this thing is clean got it home rode about 15 min and it over heated I have checked the water pump belt, tried to bleed the system by parking front end up on a snow bank to make sure bleeder srew is the highest point also tried it by making the resivoir the highest point running with the cap off i have replaced the cap the heat exchangers are warm so it seems to be circulating properly i hooked a coolant system pressure tester up to the over flow hose and pressurized the system with cap in the all the closed position it will only hold 4-5 psi with it on the first notch that you have get over it will hold 11-13 psi (the cap was a 13 psi cap) so if figured the tank was bad and went for a spin with the cap in the spot where it seemed to be good an about 20 min into playing around temp light is on again :mad2: so i stopped opened the hood and at least it is not coming out of the over flow so i closed the hood and the temp light is off now which seems much better than before so my question is did hey have issuses with the tanks?

seems unlikley to me

any suggestion are welcome and appreciated i am starting to get frustrated

ok thanks i am going to order a new coolant tank i think that is the problem

should have posted this a while ago but i got it fixed the nut that holds the water pump impeller on never got tightened at the factory and it stripped out the impeller on the pump shaft it would circulate at idle but as soon as you give it any rpm it would not turn the impeller i am guessing that is why this machine only has 800 miles on it