Abstract: A heat exchanger unit (10) comprises a core (25) and manifold (22, 23) assembly (14) mounted in a rectangular sub-frame (13). The sub-frame (13) comprises a U-shaped member (20) the opposed limbs (24) of which form confronting channels receiving side portions of the assembly (14), and a cross-member (21) secured to the assembly (14) and releasably secured to the ends of the limbs (24) to complete the rectangular sub-frame (13) and retain the assembly (14) in it. The unit (10) is fitted to a vehicle with the U-shaped member (20) in an inverted position so that with the cross-member (21) disconnected from it the assembly (14) can be slid into and out of the sub-frame (13) from beneath the vehicle.