I've got a mild modified '90 8v, and I sit about 98 at 70mph, down to 94 if I'm stuck behind a caravan

If I'm having a spirited drive, hard accelerations lots of braking etc, then it can get to 104 on a warm day!
I'd say check the wiring if you think it's wrong, but if it has correct oil level and is well maintained then I'd use the temp as a guide rather than an absolute figure, ie if it really goes higher than normal or doesn't warm up at all!.