I went and did a minor flush on my mazdas rad...I cleaned the res and filled with clean water has some antifreeze. i ran til almost hot...heater works better,but now res is full of foamy dirty water/antifreeze..so does it need a full flush or do i have something else going on. Im not sure when anything has been done to this lil car and i wanna keep it going for a lil while longer

 

I'd flush it all out, fill it up with the proper antifreeze mix, and report back... Drive it for a bit afterwords and let us know how things are going.