Instead of wrapping insulating material around the thermostat try this:
A word of caution to those six cylinder BMW owners who have drilled out the holes in their friction fan couplings to lock the mechanism up with M6 x 30 mm screws
The simple $60 overheating solution.
Check the solder joints that hold the radiator core and top to the side mounting plates. This joint can break, allowing the radiator to fall back into the fan, self-destructing both.
A heater control valve can easily become fouled with grit and sludge causing it to operate sluggishly, so these tips will help you replace it successfully.
Does your heater control valve have a leak you don’t know about? Here’s how to find out.