it hasn't overheated....yet

alright. its an 89 4.0 wagoneer with aw4. i started it up this morning and had it running for about10 minutes while i drove about 2 miles through town.the temp jumped up to about 220 or so and then came down to 210 but then went back up. i thought thermostat so i went and bouthg a new one and installed. but i just drove it not too far and it did it again.it gets real hot sitting but then i drive and it comes back down. it hasnt hit red yet. oh asnd its a clo0sed system still. until i get the cash and find the parts. any help at all would be greatly appreciated

Thanks!
Mike

oh! i almost forgot, i changed the water pump 3 months ago along with the thermo housing and lower rad hose. also the bottle is new and hasnt been cracked and i burped it pretty well when i refilled it today.