Car radiator with plain water = rusty water over a short time. Car radiator with antifreeze solution = long term health of cooling system. For best results use the antifreeze straight out of the jug, don't mix it with water before putting it in the crock pot. Also use low heat on the crock pot. The older original ethylene glycol blend works better, IMHO, than the newer more environmentally friendly formula.

If still in doubt do a search on here and you will get more reading than you care to do on the subject.

Ed M.