Hi guys in the last week or so my engine has been taking up to 3 times as long to reach 90c on the gauge but once it's there it stays there even on the motorway. She's a MK1 vrs and the stat was changed less that a year ago with an oem one & only covered 4k since. Also the cts was changed a month ago again with oem. I'm leaning towards a failing stat but want a second opinion before I start dumping coolant. Thanks in advance.

Does sound rather like a stuck open stat.