410 running too cool

[David C]

My 410 is up and running quite nicely now but the temperature drops to about 55C on the motorway at 70MPH. I thought the thermostat was to blame so swapped out for a new Gates 82C unit without any change.
I have checked the temperature gauge and that seems fine. The car runs at around 70 to 80 on A roads and around 80 to 90 in slowish traffic until the fans cut in.
I have a transmission temperature gauge and that shows around 60 on the motorway and up to 90 or so pottering around the B roads.

Any suggestions?