Re: Antifreeze and phosphate

[zm@mhcnet.att.com (Zafer Mehmood [209])]

Jokes about tasting antifreeze aside, my understanding is that phosphates
in the antifreeze eventually tend to build up deposits in the cooling
system. This was the explanation given to me by technical support
people at Prestone and also at Mercedes Benz. MB also specifies a 
phosphate-free coolant for all their cars. Seems like this phosphate-free
requirement comes from German car manufacturers only. I haven't seen
this requirement from US or Japanese auto makers. I don't know if the
alloys used in the manufacture of Audi/MB engine head/block react adversely
with phosphates or what. Or it may be that phosphates combined with
hard tap water used to dilute the coolant will cause deposits in any engine,
but this is an issue only in high mileage cars (and we know Audi and MB
engines easily last 200 to 300K miles).

In any event, its prudent to use phosphate-free coolant in Audis. I go
one step further by using distilled water (available at most pharmacies
relatively cheaply) to dilute the coolant.

How do you know which brands of coolant are phosphate-free? Presume
that the coolant contains phosphates unless the container says its
phosphate-free. Audi's Autobahn coolant, Mercedes coolant (sold by
MB dealers) and Prestone's Long-Life Phosphate-free coolants are safe
to use in your car. I've heard that Quaker State also makes a phosphate
free coolant, but it is hard to find.

Zafer


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Zafer Mehmood				   AT&T Bell Laboratories
zm@mhcnet.att.com			   Murray Hill, NJ