Radiator temp and heater fluctuation

[Dino]

I took the Charger to work this morning. It was just shy of 20 degrees. The heater works well, but only when cruisin. At higher speeds/rpm it doesn't seem to do so well. As soon as you start coasting, you can feel the heat rush through the vents. I also had a few instances where the water temp would go from 185 up to 205-220, and right back down. I'm not sure what's going on. I noticed the heater do this a while back when it was 45-50 out. I don't think I've ever seen the water temp do this. I flushed the system a while back. Do I have air in there or something?

[70 sublime]

Sounds like thermostat doing what ever it wants

[Dino]

I didn't think of that. I'll replace it. Thanks! 

[Wingnut426]

I had that problem once, the lower hose was sucking itself closed. I forgot to swap the wire/spring from the old hose before replacing it.  Put the wire/spring in the new hose and it was fine after that.  WINGNUT

[69hemibeep]

I agree with the lower hose.

[b5blue]

I got my spring from a Mustang shop online.

[b5blue]

https://www.cjponyparts.com/lower-radiator-hose-spring-stainless-steel-small-block-mustang-1965-1973/p/HW769/