Drove the jag 2 hours up north over the holidays and had to stop several times. Problem is that the car doesn't blow hot air like you would think it would only warm enough to defrost the windshield on top of that the temp gauge stays down around the cold Mark and then about 50 miles on the highway shoots over to hot so I stop turn off the car and about 30 secs I turn the car back on and the temp gauge is back at the cold Mark. Is this a bad temp sensor or a bad thermostat?

 

The first step is to make sure that the water level is at the correct point in the expansion tank. Make sure it is full and the air has been burped out of the system.
The first sign of low water is loss of heat. The system is a low volume/high velocity design.
The second step is to conduct a pressure test after the vehicle has sat over night. You also need to get the expansion tank cap pressure tested.This will locate any minor leaks.
Once you know that the level is good, the air is out of the system, and the pressure test is satisfactory and you still have the problem then I would look at the thermostat.
If you decide it is the thermostat I would recommend replacing the upper radiator hose assembly. It is about $100.00 from SNG Barratt and comes with the hoses, pipes, thermostat and all seals

 

This is another problem im having I did fill up the expansion tank but the hose that comes off it doesn't seem like I has any pressure to it. I feel like it's clogged? Or just needs to be burped. How do I burp the system?

 

https://www.jaguarforums.com/forum/x...system-106516/

Bleeding the cooling system

 

I forgot to mention that when I have the car running at idle for a period of time I get relative warm air but once I start driving the air blows cold so idk if that indicates a thermostat or the system needs to be burped, I did however check the system for any leaks and I didn't find any, going to pick up a thermostat will update if problem doesn't go away

 

It sound like the faulty thermostat stuck open to me; When idle the coolant circulate slowly and no air moves through radiator thus the engine compartment so the coolant get warmer (that's why when car over head it got hotter at the red light) but not hot enough to activate the cooling fan, when you go fast on the highway the air moved fast through radiator and engine compartment with the coolant constantly circulated in the engine, that's give you the cool air. I thermostat stuck closed you would get engine over head. I suggest you replace the thermostat and flush the coolant and heater core, replace with Jag or compatible coolant.