wrote:

> > wrote in message
> ...
>
>
> and I didn't realize until just here recently that the silicate in the
> yellow jug of
>
> prestone coolant was hostile to water pumps. this situation may not be
> peculiar to only prestone.
>
> m h o
> v fe
>
> Look...lets see if we can get it a little straighter.
> Silicate has always been in 'green' coolant and its purpose is as a
> corrosion inhibitor for aluminum parts.
>
> Some water pumps have been made of aluminum.. Nicht wahr?
>
> Silicate is not intended to protect iron or steel.
>
> When excess silicate was used in a formulation, or when certain types
> of hard water were used to fill the radiator, silicate precipitation could
> be problematic.
> (Magnesium in the water is particularly incompatible.)
>
> Precipitates are never good in a cooling system.. They can block
> radiators, AND they can be abrasive. MANY times I have seen
> radiators plugged with silicate precipitate. It is DIFFICULT to
> remove.
>
> OAT technology, as used in Dexcool, did not contain silicates. That
> was seen to be an advantage in one sense, but probably did not provide
> the protection to aluminum parts that was desirable.
>
> Therefore Hybrid OAT , or HOAT, evolved. HOAT contains silicate,
> but in reduced amounts compared with the older green formulas.
>
> The city water here contains little magnesium or other hardness ions.

Or one could go the typical Japanese manufacturer's route.
They seem to prefer silicate-free but with good amounts of
phosphate. Phosphates are supposed to be real problematic
with hard water though.