Saw this over on the XF forum and wondering if 4.2 S-Types have the same problem:

"The water outlet housing that contains the thermostat is a know problem on the 4.2 litre NA engines. It is wise to replace the outlet assembly each time the vehicle has a coolant change as if it cracks and the engine overheats due to coolant loss, it may cause catastrophic damage to the heads and cylinder block.

The water outlet pipe comes fitted with a new thermostat, gasket and water temperature sensor. "

Is this something for S-Type owners to consider having routinely done?
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Jaguar: Grace, Pace, and Space - Sir William Lyons
'08 Jaguar S-Type 4.2 "Satin Edition"

 

Definitely yes for the NA engines.

 

I had to do this repair last November on the 4.2 engine in my wife's 2006 XK8 when the thermostat housing began to leak. The black plastic coolant outlet duct tends to warp and leak as the heat cycles and the passing of time take their toll. Plenty of instructions here on the forum on how to most effectlively do this repair. Getting to the two rear bolts on the coolant outlet duct is the biggest challenge. You need a small socket drive set (quarter-inch drive). Normal-sized tools take up too much room and can't quite get to the tight spaces....