A heat exchanger with a core, a support structure and a mount. The core is variable in size and has a lower temperature fluid port and a higher temperature fluid port. The mount is positioned between the core and the support structure, adjacent to the higher temperature fluid port. The mount restrains the core relative to the support structure, such that when the core varies in size it does so either away from or towards the mount. The heat exchanger can also include a deformable connector, including a bellows, a flexible hose and a braided metal hose. The deformable connector is positioned in a manner which allows it and lower temperature fluid port to remain in fluid communication as the core varies in size.