The A/C blew cold air when I started driving. After 30mins, the A/C blew hot and the engine temp gauge went to the red. As soon as I turned A/C off, the gauge dropped to the middle. When I turned off the engine, the fan was still running. There weren't any check engine lights or warnings.
Please help!! Thank you.

 

Your engine was very overheated if the gauge went to red. Most likely problem is a failed thermostat housing. Very common fault, the plastic breaks down internally and the cooling system can't keep the engine at temperature. Replace the housing; comes with a new thermostat and sensor.

 

I would go a little further than mhamilton's sound suggestions. You may want to get the car towed to the Jag dealer to fully diagnose why your engine overheated. Based on your location, it looks like we would use the same dealer. As you probably know, these Jag engines are very expensive to replace, and being Al, they do not tolerate overheating at all. The Jag engine temp guage is computer managed, and will only shoot to red when there is a big problem. Hopefully you shutdown fast enough. Good luck, and let us know what it turns out to be.

 

+1. Do not drive it. Repeated overheating can be very detrimental to the engine.

 

Rhanky,
Just curious whether you ever resolved the issue you described where the A/C blew hot, the engine gauge showed hot, and no warning alarms? My 2008 XJ had the exact same things happen to it last week. I have been driving it some for about 4-5 days since it occurred; the issue has not occurred again. I also had an authorized Jag technician run the diagnostics & a check of all related to the A/C coolant system. The tech did not find anything wrong. I purchased a new thermostat & housing to keep on hand & have been watching my engine temperature; so far, so good.

 

One failure mode of thermostats is intermittent sticking. It probably would be wise to have it replaced proactively.

 

It wasn't me with the problem. I was merely responding to the OP.

Personally I'm not sure what you are waiting for before replacing the t-stat. I would install the t-stat and get the coolant flushed and replaced, and know you have ruled out the most common failure point in our XJ cooling systems.

My 04 XJ was starting to give symptoms earlier this summer that it was running hotter than normal, noticeable when idling on hot days and sometimes stumble a bit with hot restarts. The dealer didn't think a t-stat or flush was necessary, but the engine has run a whole lot better heat wise ever since.