Mineral deposit buildup will result form using tap water... This will cause clogs and corrosion in your cooling system, resulting in premature failure of the radiator as well as electrolysis in the head's cooling passages blowing the head gasket.

Use any quality green coolant with distilled water for best results.

"A young man who does not have what it takes to perform military service is not likely to have what it takes to make a living." - John F. Kennedy

Proud owner of an 88 Montero (with a blown engine).