Hi. Has anyone had issues with their heat not working properly with higher mileage IS250's??
I have 205,000 on it.

To add a little more substance to my situation. I had my thermostat changed by my routine mechanic. The heat worked for 3 weeks. After that I brought it to the dealership and they claimed my heater core was not functioning properly due to the neglect of properly flushing the system out. They did this and tested a few issues and stated their was no cracked headers which could be causing the inconsistency with the heating system. I paid them and the heat worked well for 1 month then it started only working when I was on the interstate traveling at higher speeds.
A friend of mine and I unplugged the heater core hoses and I flushed out the core with CLR. This was recommended by a mechanic friend.
Around town it was blowing cold air.
A few weeks later, I changed the out the alternator and the cars working great but the heat mostly blows cool air, typically set 80 deg.

Does anyone have suggestions or can add insight here??
Thanks in advance