93 celica GT thermostat problem

My friend has a 93 celica GT convertible that he just bought. the heat wasnt working too well so he thought the thermostat was broken. When he went to replace it he realized it wasnt even there. He went to the dealership and a bunch of auto parts stores, and they all gave him the same thermostat, but none of the thermostats fit. There were all just a little too big to fit into the engine. Even the part from the dealership did not quite fit. Whats going on here? Has anyone else had this problem before?

yea i had the same prob sept my thermostat was good so i replaced it n my celica kept over heatin so put the old one in still no heat so it might not be that but u deff need a thermosat fer heat well u try ebay?