2012 tdv8 pipes going to the matrix are cold . I recently changed the oil cooler , have I got trapped air ??

Try bleeding the system again, sounds like an air lock

Thank you . What’s the best way to bleed it ?

The process is in the manual & can be down loaded from the Wiki files. If possible park the car up hill.
I have used this process, but I also run the car up to temperature with the expansion cap Off & the bleed valves undone, (until coolant comes out of the bleed valves & the expansion tank starts to overflow ).
Switch it off & let cool down ( top up as necessary).
Then run it up to temparature again with the cap On, let it cool down & top as necessary. That shoul be adequate, if necessary you can repeat the process.