Are you sure that anyhting is really wrong?
At highway speeds with 80F temp and 80% RH using A/C, staying around 95-100C is not bad!
Check the coolant ratio for yourself and make sure it's no more than 50/50, preferably 40/60 (af/water) ratio.
If you think something is still wrong, check the thermostat!
Wonder what a roar test is? ROAD???
Regards . . . . JimF
'94 S500 Cpe
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