How important is it to use distilled water in a radiator?

[4x4mike]

Long story short I'm doing some maintenance on our 2005 Subaru Forester. The radiator flush is a PIA and I still don't know if I've got it right. The engine is turbo charged and there are a lot of cooling houses and a couple different reservoirs. One of the troubles is air pockets.

Anyways, I was getting fed up with it last night (3 hours, past my bedtime, in the driveway soaking wet) and used the garden hose. The guys on the Subaru forum said it's a big no no and said to drain it and use only distilled. The radiator is the stock aluminum and it sounds like the system is prone to blockages. I guess the minerals in the tap water are the trouble makers.

What do you all think? Should I change it all? Basically start all over and end up in the driveway tonight laying in hot coolant and water.

Same goes for the 4Runner. I'm on schedule to change that this weekend and had planned to use distilled. I have used tap water in every vehicle I've ever owned and never had a problem, that's the reason for the question.

[CJM]

i always used tap water and never had an issue, but then again I usually flushed every 2-3 years anyways.

[corax]

Tap water is fine unless your water is anything but clear

[4x4mike]

Well I ended up draining the systewm again and using distilled. I didn't want any clogs with is pretty common with this vehicle. The fact we haven't had any gave me reason to do it. Service interval for the coolant is only 30K so that leads me to believe that it gets worked over.

[YotaFun]

I have always thrown distilled in my vehicles, just to be on the safe side, I mean I have heard stories and what not but I would rather be safe the sorry.

[4x4mike]

Our water is clear but I know it's got stuff in it. There are many documented (owners and Subaru Corp) cases of head gasket failure on these engines. We have a super uber warranty but I don't want to give the dealer a reason not to fix it if it comes up. I'm doing the 4Runner radiator this weekend and wanted to work out all the bugs on our other car before I go at it.

The dealer only sold me one bottle of coolant for the 4Runner. I'm wondering if that'll be enough. I plan on draining the radiator and then topping off the system with distilled and driving around for a day or 2 (this only adds up to 10-15 miles). Then drain again and repeat is necessary. Then mix in the coolant when I get clear and clean from the drain.

[04 Rocko Taco]

TO help with the radiator flush, instead of just driving around with distilled in, use Prestone radiator flush, I've had good luck with it in the past, and just FYI - I have never used anything but tap water and have never had any issues. Distilled is a good way to be safe and not sorry though I suppose.

[strykersd]

This might be a stupid question, but why not just run coolant? I'll run water after a swap an engine in or something along those lines to check for leaks, but other then that I always run coolant.

[04 Rocko Taco]

straight antifreeze? No water? Or do you buy the premixed 50/50?

Antifreeze keeps things from freezing, but doesn't cool very well on its own.

[CJM]

Premixed is nice too, but the full dose is cheaper and you get more out of it usually.

Protip: use your fridges water source if you got one, its filtered :)

[Seanz0rz]

i always use distilled (thought i dont have to worry about that with an air cooled VW!)

even filtered water can be high in calcium and other minerals which build up in the coolant passages.

i wouldnt use anything but distilled unless it was an emergency. thats just my personal feeling on the subject.

[Crinale]

iv heard that distilled is best, but soft water is a close second... so i use soft water in my vehicles... (since my parents house has good soft water)