https://www.jaguarownersclub.com/forums/topic/15487-27-d-s-type-instant-coolant-loss-on-motorway-any-help-please/?fbclid=IwAR1r7JvZMKE0zMdktG9aNr4DoRybEZhH83_NQuwvBDIESHtwcYvMRtNRobA Check out this link on the Forum it may be the same trouble you have, smae thin happened to me and I'm just waiting to hear if that was the problem