Having owned my XK8 for about 4 years, I had an ongoing issue that I could never find a solution for. When the outside temperature fell below about 40 degrees, cold air would pour over the dash and onto my left hand. It was outside air that I assume was blowing on the windshield. When the temperature fell below 20 degrees the car was unusable. It was like having the window open with the cold air blowing in. I did read on this forum that other people had the same issue but never found a solution. This year things changed. No longer is the cold air flowing off my dash board. My car, so far, is acting like a normal car. You get in and within five minutes the car is nice and warm inside. Now the weather has only gotten down into the mid 20’s so far in Chicago, but the cold air issue is gone.
Over the summer, my heater control valve started leaking so I replaced it. ALSO, when the weather first started to get cool, in the low 50’s, I noticed that I had no heat in the car. My first thought was the control valve wasn’t operating, but feeling the hoses, it seemed to be working. Then, by reading this forum, I decided to back flush my heater core. Not a bad job and it did the trick, more heat than I ever had. I am not sure if this had anything to do with fixing my cold air issue, but I have to think that either the valve or more likely the heater core back flush fixed it. I just wanted to share my story in case it could help anyone else.

 

Good information, thanks.