[V6-12v] okay so i still don't get it

[Clive Young]

still have no heat in the audi after like 3 years umptine hoses , water pumps thermostats , a heater core and a flush and fill .. mabe this think will NEVER heat .. 

But 

it was -10 the other day and the heat was cool even at highway speeds. The thermostat was sitting at about 70- 75C. Given the Thermostat is not suppose to open till 87 should this have been the case ? can anyone tell me what the temp of their car is at in similar conditions ? This is the third thermostst so I doubt it is not working but you never know.