Coolant Change--Distilled or Tap water????

Everyone recommends distilled because this is safest, pure water and nothing else. Then add the appropriate ant-freeze mixture even in the summer. Anti-freeze does not just stop the water freezing, but increases cooling efficiency too.

If you are going to use tapwater, which we've all done in an emergency, boil it first. This will drive out a lot of the dissolved oxygen and reduce the hardness a little if limescale is a problem in your area. Reducing the oxygen content helps reduce corrosion.

Alec Wood

From owning a number of vechicles and heavy equipment, replacing radiators, pumps, hoses and such and having seen the rust and other minerals in water from running a community well, USE distilled water. Yes, rust is an issue, but the big issue with tap water is the minerals. You don't need the metals and other minerals in the water. They cause the deposit and gunk you see after you have flushed a cooling system or look at a heater core. With the metal radiators after a long period of time, they will fail from rust. You will experience cracks in the metal seams, etc.

If you don't a pure water store in your area, the distilled water from wal-mart or any other store is fine. If you're going for good tasting distilled water, the pure water stores are the best. After the water is distilled, they run through a micro filter. I use to know the size, but it give the water that clean water from the mountain refreshing taste.

Also, for your lead-acid batteries, distilled water is better for the above reasons. I have brought a good battery like NAPA's and DIEHARD's back to life with distilled water and a 8 hrs charge.

Tap water is fine, distilled is for the battery

More important than the water is knowing not to use green antifreeze in a Behr (Mercedes) radiator.

Your memory must be faulty. The 'good' taste of water comes from mineral content. Pure water tastes pretty terrible.

Plus -- despite the issue of mineral content -- I am not aware that purified/distilled water is used in the coolant system. The key is to use the right mix of water and anti-freeze all year. BTW, very pure water can dissolve minerals from pipes and containers.

DAS

I've always used 50% tap water with 50% antifreeze and have never had a problem with any vehicle. In fact, until this discussion, I have never heard of using distilled water for coolant, only for batteries, where I agree, it is important.

I change the coolant every 3 years or so and I think that is far more important than which type of water you use. All today's antifreezes have corrosion inhibitors. And the point made about rust being an issue with tap water is dubious. Rust is formed from the oxidation of iron. Without corrosion inhibitors, that will occur regardless of the type of water used.