For some time now, I have read a number of reports on "leaking of the overflow/expansion tank" on most of the current Jaguar cars, at least in the 2000 to 2009 models. Maybe others.
I have an 05/XJ8L and over the past few months. have noticed the same thing--although a small amount, I have not considered it a very serious thing, for as soon as the coolant cools, the leak will stop. It happens only after a drive and the car being shut down for a few minutes. This is caused as the coolant builds high temp. pressure and the coolant pressure bleeds out, or back into the system. This leak is at the exit/entry nipple on the top left of the tank.
Today I decided to have a look as to way it leaks, and removed the spring clamp on the rubber hose and slipped the hose off the nipple. The nipple is cracked about 1/8 of an inch out from the tank. Much more serious then expected. From what I have read in the past, this has been the part that breaks and reason for the leaks.
Once seeing the nipple, it is so obvious as to why this thing is cracking/breaking, that a high school student in his first month of "shop" can see the reason. The thing is much too long. It must be at least 3/4 of an inch too long. Once the rubber hose is slipped back on and the spring clamp is back in place---which should be near the tank, you can see the bulged end of the nipple much to far outward in the hose.
What the extra length does, is allow constant forces on the nipple from the hose which is not sucure, which allows it to bounce, or move around as the engine torques or vibrates under normal starting, stopping and driving conditions.
Although my car is just one of the vehicles this tank is used in, the length of this nipple is more then likely standard. A shorter nipple with the bulged end just beyond the spring clamp would end this cantilever effect on the nipple, and more then likely end the cracking. Cutting the length of the nipple would do the same thing and/or finding a way to secure the tank end of the rubber hose would even be better.
Jaguar should have known this for a while now, but has just not taken any action to fix the problem. I know, to change a design is costly, but to forget a safety issue is also costly. This problem needs fixing and Jaguar should bite the bullet and fix this.
IMHO
Garfield