Peter, Guy, Nigel,
Many thanks for thoughts, comments. The 'temp gun' is sensible. Apparently my garage has one on order, they'll call me in to run that check.
My sender was replaced last year, so that's all good. I think the whisps of steam I noticed have thankfully, and mysteriously ceased... Will check today.
Your kind offer of the HPH cluster I will keep in mind. May come to that. That's a job I can attempt myself! Maybe my gauge suffered permanent damage when my gasket blew, going hard into the red. Now, maybe entirely recalibrated! If such a thing can happen... I'll have to learn to live with inaccuracies for now. J