Technically yes you are supposed to used distilled water because of the impurities and sediment and so on that are found in tap water. At work we use straight up tap and we don't have any problems with it... Specially because iti becomes distilled water after a day anyways. But for OPTIMUM protection distilled water is the way to go. I personally don't use it either.

 

it's a chemical reaction between the tap water and the specific anti freeze. the five year stuff has extra addatives that make it last longer but react with the tap water and makes the **** in the water filter out and settle in the radiator. i bet if you looked at some of the other anti freezes out there they would say to use any water, and some would say to use distilled. it's all about the addatives and other **** they put in that crap.

i bet if you put tap water in again with another brand of anti freeze (something cheap and not designed to last five years) you wouldn't have the sludge build up.

 

General Motors faced massive lawsuits because of the orange stuff. It was wreaking havoc in the V6 engines of the S10 Series trucks, Astro Vans, and other vehicles. My Cavalier came with the orange stuff and it now has 106K miles on it. The owner's manual says to change it at 150,000. I have not had any problems, which surprised my local Chevy dealer. When switching to orange, or from orange, the system MUST be flushed thoroughly. Green and orange coolant to not mix well and will destroy your engine.