Thanks again.
1) If I use DT = 208 C the expansion is 16500 x 15.48X10^-6 x 208 = 53.12 mm
2) If I use DT = 17 C, the expansion is 16500 x 15.48x10^-6 x 17 = 4.32 mm
The mean coefficient of expansion is between room temp and the final heated temperature above room temperature.
That is , the metal expands above room temperature, (it does not start expanding from -170 C, it starts from room temperature and then expands above). Hence (1) does not appear to be realistic.
Please advise.