If you have an older Jaguar, you know that engine heat is something your vehicle produces in abundance. You're probably also aware that the Jaguar heater core is capable of acting as a small auxiliary radiator should the need arise. Newer Jag owners may have no idea what we're talking about, since they've never experienced the overheating, corrosion, and Jaguar heater core leaks that the average XJS or XJ12 owner has learned to live with. So lets start with a basic Jaguar heater core primer. The Jaguar heater core is a small radiator that sits beneath your dashboard in the ductwork that supplies your cockpit climate control system. In the summer when you have the temperature control to 'cold,' no engine coolant flows through the Jaguar heater core, so it doesn't warm up the air passing through. In winter, when you crank the heater up, a valve under the hood opens allowing hot engine coolant to circulate through the Jaguar heater core. As interior air flows over it, the Jaguar heater core transfers that heat to the air thus warming your cockpit. Since the Jaguar heater core transfers engine heat to the ambient air, it was often employed in the past by Jag owners as an overheating prevention aid. Since cars generally overheated in the summertime, using the Jaguar heater core in this way made the cockpit stifling hot, but that was the price of Jaguar ownership. These days, the Jaguar heater core is no longer required to serve as an auxiliary cooling device. However, it still requires periodic maintenance in the form of regular coolant changes. Follow the manufacturers recommendations for this service. Finally, if it's too late and your new or old Jag requires a new Jaguar heater core, save money and still get OE quality by purchasing your new Jaguar heater core from us.