Everytime i fix a leak I'm the cooling system it leak from some where else....
Octo hose, throttle body hose, thermostat housing and 2 years later the thermostat again it's leaking from the side JB Weld or something. At first I thought it was just because of Old parts. my jag has the 4.2 engine 06. Any suggestions.

 

Not sure on your year model but check and see if the aftermarket metal thermostat housing is available and replace the plastic one. This is a common "must do" on the 4.0 motors.

 

Before I bought another plastic housing I looked for the metal replacement, I never found it for 03 and up. So i put on another new factory Tstat housing.

 

JB Weld is a band-ad and not made for a permanent repair. The engine and coolant system gets hot and the pressure associated with it will breakdown any weak spots. Replace the housing.