I changed the overflow tank on my 2003 s type. There are now no leaks, but the fluid level drops slightly each day for the past few days since the tank was replaced. Is this just from getting the fluid back into the engine and will stop soon?

 

It should... Keep an eye on it though.

Did you put a pressure tester on the cooling system to confirm the absence of any leaks, or is your comment based upon casual observation?

Also, when you have a minute, please head over to the New Member's Forum and post the expected "introduction". Doing so will get you additional forum privileges; it can be found here:

New Member Area - Intro a MUST - Jaguar Forums - Jaguar Enthusiasts Forum

 

It could be air in the system working its way out. Changing that tank is an invitation to extra air. At Operating temp, turn the heat wide open, open the bleeder valve by the tank and you'll see the very small bubbles. Takes about 30 minutes to get most of it out. Good luck.

 

Give it time. Had the same thing happen on my STR after the fluid replacement. It can take months for all the air pockets to clear out.

 

Beforehand, simply suck out the coolant using a large syringe and then change the container. This saves ventilation. I would vent properly as David described 1*.
Did you have to refill? The container is not full to the top. He deflates himself to the desired level.
Greetings, Willi

 

Totally normal. It took mine months to level out for the second time.

It is definitely unnerving as you assume there may be a leak. As long as you don't see drips and don't smell the coolant after a hot run, you should be as good as gold.