1993 Buick Century no heat at idle very little at speed

OK new news I flushed the system and bam I got heat but only for like 1 hour then I puled over and popped the cap and wouldn't you know it was foaming like a rabid dog turns out a guy told me when he seen it that I need to do a chem flush and a major one at that I hope this helps any ideas on this oh and yes the fluid that came out was brown when I flushed it but I put new green in it plus I believe he might be right because on the way back home when I floored it I had heat but at normal speeds not so much not cold but close

one more thing I had to Frankenstein the flush because the drain plug would not allow anything through I even pulled it all the way out I believe
there is sludge in the system someone put red antifreeze in it before I owned it looked really bad

and the electric cooling fan keeps coming on like riht when you turn on the key and then off then back on then on for a long time then off, on, off, on could the sludge be causing the censer to fail or do I need to look at the relay