2002 A4 3.0 6 SPEED

I have been having a problem with my heat the last few years. I live in Wisconsin and when I am on my way to work my heat will not kick on at all. It seems to work when the temp outside is around 50 degrees. If I take my car on a long drive, (last weekend to Chicago) about half way there I can shut my car off and go get food or whatever, and it will suddenly work. For the rest of the day no problem. Then I will park it overnight. Get in start it up no heat.

Thoughts

It cant be the blower motor right? It blows great, sometimes.

The heat is as hot as you could ever want it to be when it works. Its not blowing warm or cold air. ITS HOT when turned all the way up.

The coolant in the vehicle has to be G12. I purchased a gallon of g12 from the dealer and was just going to flush out the heater core and add any more coolant I need. Before I was going to do this I tested the TEMP of the coolant and it was maxed out to like -45F. That seems high. Could that be my problem? Too high of a coolant/water mix. Both tubes that run to the heater core are warm when the car is warm.

I don't see how it could be a thermostat because the heat gauge when warm is always the same right in the middle.

I also know about the flap that is in there too. I have done much reading and investigating and don't know where I should start. Any help would be GREATLY appreciated.