So the story begins with what I have its a 05 xjr 4.2 charged.

I changed the thermostat
I had a pinhole in one of the hoses sleeved it

Replaced the coolant with pentofrost sf slight mix with water

I've been revving at 2500 over and over with bleeding screw off I even took the pressure cap off the reservoir and repeated the car gets blazing hot but when I stop acceleration and put the bleeder screw back it gets cold again.

Am I missing something I'm tired of wasting my coolant haha.

 

Not quite enough info ........

Which hose had a pinhole?
What gets cold when idling - the engine or the heater or the heater hoses?

 

It's a hose that I believe goes to the heat exchange in the car and the front half is a y that goes to the bottom of the reservoir and the other to the large thermostat gooseneck setup.

And the air blown through the car is cold

The car gets to the mid point on the dashboard thermostat

 

Sounds like the heater pump has failed (very common). At higher revs the car's water pump can push hot water through, but at low revs it isn't man enough.

Follow the pipe down to the pump (mounted on the chassis rail) and replace it. If you buy a 2nd hand one test it before putting it in.

 

Hmm ok I was thinking that but wasn't sure didn't want to start shotgunning parts. But okay I'm get a replacement change it and keep you posted thanks for the help!

 

Also can you give me a little guidance on the replacement never changed one before

 

Had heat issue with my 04 xjr. Had heat in the middle vent but cool on the side vents, and go colder when at idle. ended being the heat pump. I had the dealer do it.

 

Ordered this

http://m.autopartswarehouse.com/details/Jaguar/XJR/OES_Genuine/Auxiliary_Water_Pump/2005/Base/8_Cyl_4-dot-2L/W0133-1656109.html

 

The pump is mounted on the L/H chassis rail just in front of the bulkhead (on R/H drive cars). Unplug the wiring, unclip the hoses, remove the mounting bolts, and struggle for 2 hours getting the pipes off!

You will lose a tiny drop of water - top up your header afterwards.