|"The Sting" (4ACV12)
The radiator is a source of heat. Models of it have been seen throughout the series, and do not differ much from their early versions. In the building used for the 3001 Miss Universe Pageant on Tova 9, Fry made out with one, believing that it was an Alien from the radiator planet (2ACV06). During Turanga Leela's coma-induced dream at Fry's funeral, along with Fry's girlfriends, another was also seen (4ACV12).
The radiator starts a running gag involving Fry believing that all objects are aliens shaped like objects, ironic in a universe filled with aliens that look like various everyday things, a gag that is outed in season 6(6ACV18), when Leela tells him "Once and for all Fry, even though it's the future, most objects are still just objects, not aliens who look like objects".
Fry: I just made out with that radiator woman from the radiator planet.
Leela: Fry, that's a radiator.
Fry: Oh. [He clears his throat.] Is there a burn ward within 10 feet of here?