It seems I have an air pocket in the system and I was going to add some more fluid. However when I unscrewed the cap from the overflow I noticed a couple of things. I noticed the overflow was loose and jiggled. Also once you unscrew the cap it does not come off freely, I just had to pull it off once I felt I was passed all the threads. Is it like that on purpose?

 

no, but normal, or common whichever word you prefer

 

Mine is difficult to remove also. I use a large long screw driver to leverage the cap off. You have to be very careful so you don't damage the tank. It's also hard to get back on.

 

What about it being loose? Also I would imagaine it is not a good thing to open when the car is hot. But when the car is cold the tank is full. Should I run the car with the cap off to get the system to suck the fluid in?

 

why do you suppose you have an air pocket?

 

If I am not on the accelerator the heat blows cooler. I had already posted here somewhere to confirm it. But then we got into an antifreeze discussion in reference to the dexcool and the jaguar fluid. It seemed to be a 50/50 spit - what do you think? Better yet what is in your radioator and for how long? Can Jag fluid and DEXCool be mixed? This is so confusing - I am the 2nd owner, bought the car from a Jag dealership, but who knows what they did. I have close to 60k miles.

 

If by chance there is some air in your system you might try the clamps on the heater hoses that Dennis explains in his coolant change article.
As for what type coolant to use. I am using Prestone Extended Life w/Dexcool 50/50(some people say not to use this stuff). It's been in for about 4 months now without any problems that I can see. It still looks clean in the resivor. I wouldn't mix any different types of coolant by just adding to the old in your system. Of course there will always be a small amount of old left when you change but that won't be a problem. What I did was to drain it once then a week or so later I did it again to remove as much of the old as possible.

 

Prestone Extended Life is fine to use. It says for ALL MAKES and MIXES WITH ALL TYPES of coolants. I don't think Prestone would make a such a claim if it was going to cause a problem.
I have not changed my coolant in the Jag but have used Prestone Extended Life in other vehicles with no issues for years after. However, even though Jag coolant is $55/gal it is not all that expensive when you figure it only needs to be done once ever 5 years. It is a matter of choice and I do not feel you can go wrong either way.