shit, my accord used to do that..... We'd replace thermostats, hoses, etc..

headgasket might need to be replaced. Thats what the main issue was with my car, anyways. But the symptoms were the same (heating up, but gas makes it go back down).

after a while, honda's coolent systems seem to go to shit. It's a trend I've noticed.....

you could try replacing your themostat, but I dunno if it will do alot of good. I'd get that headgasket checked out asap, tho. You don't want that going out on you.....