I've got a base 2003 S type with the NA 4.2 motor. I've had the car for a little over a year and have had coolant leak problems. I'm wondering if the system has too much pressure. What is the pressure supposed to be? Does the reservoir cap control the pressure of the whole system? Or does something else? What is the cap's pressure range? When I first got the car it had a minor leak. As time went on I could see it was the heater control valve. I replaced that and then after a while the thermostat housing developed a crack and leaked. Replaced that and now there's another leak. I'm not sure yet if it's the thing that the thermostat housing attaches to, which I hope is available, or something else underneath the throttle body area. Any advice would be great.

 

The cap on the plastic tank controls the whole system.

The pressure is 120KPA, from what I hav eavailable here.

Those caps can go bad if coolant flows out through the thing due to the bottle being overfilled, then they tend to jam up, and not release pressure as designed. Eventually something has to give, usually a hose.

Had an X308 do the same here a long time ago, and a new cap fixed it.