87 B2200 heater troubles

Ill try to make a long story short I had posted on here about no heat then I flushed my heating system with zerex radiator flush and wal aah I had heat.but not so fast I refill my cooling system I decided on a 50/50 mix bam no heat again .so there went 17.00 for antifreeze and flush so I reflushed again ahaa heat then refill with 50/50 another 10.00 for a jug of antifreeze and bam no heat again so 2+2 finally equals 4 when i put antifreeze in at a 50/50 mix my heat doesnt work worth a hoot does anyone know the smallest mix you can run without freezing and busting in the cold winter.the wierd thing is my heat works great with strait water but I have to have antifreeze to keep her from freezing, finally I just started flushing the heater core and card boarded the radiator up and Ive got some heat but after a way to long cold ride. anyone ever had this problem?

My bad water pump was causing this problem.