So hot it burns off copper loaded silicone (experiment to see if I could bodge the gap where the metal had rotted to frilly round the exhaust pipe) Maybe I will play with my middle'o'LIDL IR thermometer. Or strap the "spare " type K thermocouple down there with some wire and go for a drive.
Not that hot, the steel pipe holds its shape. I will try and shoot it with an IR gun when I get back home, we are using the bus today.
I was getting about 350C on No4 just out of the head, about 130C downstream of the No3 heat exchanger but 180C at the 4 into 1 where the cool exhaust through the 1/3 HX meets the less cooled path from the 2/4 rear exhausts..