The largest dinosaur, which I know is a subject of discussion, is https://en.wikipedia.org/wiki/Argentinosaurus 30 metres, 80-100 tonnes and blue whale https://en.wikipedia.org/wiki/Argentinosaurus 30 metres, 180 tonnes

If a 100 tonnes creature can live on land, my gut tells me a 180 tonnes creature could too. where's the point of no return? There's all sorts of cooling mechanisms that could be dreamt up, just as we see strange heating mechanisms (https://en.wikipedia.org/wiki/Stegosaurus#Plates).