The thermostat in a Jaguar is responsible for regulating the flow of coolant into the engine which, in turn, will help keep your Jag operating at optimal temperatures. Like almost every other part in your Jaguar, you will eventually need to replace the thermostat due to wear and tear. Because Jaguar has so many different models, the exact methods for changing the thermostat will vary from car to car. The basic steps, however, will be similar for each model.
Raise your Jaguar off the ground with a jack and secure it on jack stands.
Place a bucket under the radiator and either open the drain plug or loosen and disconnect the coolant hose to allow the coolant to drain into the bucket. Disconnect the coolant hose with a flat head screwdriver by loosening the hose clamp.
Locate the thermostat housing by following one of the two large hoses at the top or bottom of the radiator that connects to the engine housing. If the piece that the hose connects to is one solid component and not bolted onto the engine, you will need to follow the other hose instead. The thermostat housing is secured to the engine block by three or four bolts.
Use a ratchet and socket set to loosen and remove the thermostat housing bolts. You may need to move or remove other components in the engine compartment to reach the bolts.
Lift the thermostat housing off of the engine block to access the thermostat. Note how the thermostat is positioned as you will need to install the new thermostat in the same position.
Remove the thermostat from its mount and discard it.
Scrape the remains of the thermostat gasket from the bottom of the thermostat housing and from the thermostat mount on the engine block, then scrub both clean with a scouring pad.
Apply a layer of gasket sealant to the bottom of the thermostat housing then press the thermostat gasket into the layer.
Place the new thermostat into its mounting area and replace the thermostat housing over it. Secure the housing with the bolts, then replace all the engine components you may have moved or removed.
Refill the radiator with coolant then lower the Jaguar off the jack stands with the jack.