Ther radiator is getting close to 20 years old. From my experience with bishis since thats all I drive and own. The radiators tend to suck after about 20 years. It may be a 1992 or whatever but it's f'n 2010 and that thing is almost 20 years old and isnt going to cool like it did. You should be able to take a air hold an d pressurizxe the cylinder to 100psi or so, and if you see tonsof air bubbles while the engine is fo course dead it is a bhg or cracked head. Otherwise I'd say it's radiator. Taking your thermostat out can make the promlem worse as it can let the water flow too fast through ther adiator and you will end up not cooling it down. I tried it in a starion once and any time i drove it hard for any amount of time without the thermostat it would ioverheat. With a 180 in it was fine. A airhold from napa is less than 20 bucks if I remember, and worth every penny. It's basically jsut a hose with a spark plug setup and then a air hose adapter on the other end.s Set the pressure on you compresspor and not only can you check for air leakss you can change valve seals witht eh heads on the engine/