"NickySantoro" > wrote in message
> A GM powertrain engineer who used to post on a Caddy board cautioned
> that flushing is not necessary unless you have a clog of some sort.
> His suggestion was to just drain the rad and refill with 50% distilled
> water and 50% coolant, in this case probably Dexcool. The idea is not
> to introduce tap water with it's mineral content into the system.
> FWIW
> YMMV

Depends. I wince at generalizations like the one the PTE has made.

If you have a lot of iron oxide (rust) in the system, then I believe
it is best to wash it out. Iron oxide is a powerful adsorber of polar
chemicals
such as are in the antifreeze packages. The result can be a puttylike mess.

Deposits, including iron oxide, on metal surfaces can be a prime cause of
corrosion. And guess where the corrosion occurs...that's right, just where
you wouldn't expect...it occurs UNDER the deposits. (I'm sure you've seen
rusty tubercles form in iron systems exposed to water. Deposits can be a
cause of this.)

If you live in an area where tap water is mineral laden, you might want to
spend a buck or two a gallon to buy distilled water. It wont break you.
We've discussed this before. Especially if you are using a silicate bearing
coolant, it is best if the makeup water is rather pure.

In addition, the potential corrosion rate in water systems is related to the
conductivity of the water, among other things. The more conductive (due
to minerals) usually the more corrosive it is.

Where I live, the water comes from lakes and is not heavy in minerals.
(or at least, it wasn't until the state changed the treatment program a
short
while ago).