Prestone Antifreeze question for 1990 200tq

[Brett Dikeman]

At 10:31 PM -0500 3/3/03, jmcelroy wrote:
>My 200tq looks like it has green Prestone Antifreeze in it. I called the
>Audi specialist that worked on it for the previous owner, and they say that
>just about all antifreeze now days is compatible with aluminum in cooling
>systems.
>
>Any thoughs on this subject?

Most Prestone-like crap works by covering everything in the engine
with either phosphates or silicates; the idea is that metal that's
covered with the silicates or phosphates won't rust.  Yeah.  It also
won't transfer heat as well.  FYI- some "Phosphate free" coolant
really isn't.  A few of them have some phosphates in them- just not
as much.  Prestone skirts the issue on their website- claiming it's a
problem with "high mineral content in european water."  Uh huh-you're
not supposed to use tap water, so why would it matter?

Japanese companies recommend coolant without silicates; I imagine
they had concerns of some sort.  European companies say no
phosphates.  Far as I know, Pentosin meets both.

When I drained out the green crap that was in my car, not only did a
ton of rust and scale come out(there's a lesson learned- use
distilled water only), but everything that I could see in the system
was coated in yellow-white stuff, which I haven't figured out exactly
how to get rid of- I've had it on advice from a club instructor to,
when summer hits, fill the system with 100% distilled water, toss in
a bottle of water wetter(to keep the water pump lubricated), and run
that for a bit, then flush the system and check again.

When I switched to blue pentosin this summer, the t-stat stopped
sticking(tstat was pretty new, too), the water pump quieted down(and
hasn't 'gobbled' since), and temps dropped dramatically, even in the
dead heat of summer.

   There were a few other factors- the coolant was overdue for a
change, and I did a very involved flush of the system, filling,
running up to temp, then draining it multiple times(man, that was one
hell of a job, in 95 degree weather.)  I even did a bottle of the
radiator flush, since the system had been neglected. I think I also
mixed the coolant at a slightly weaker ratio, which means a slightly
higher heat capacity.

   So, it's not a good benchmark.  Would have been better if I had
done equal mixes and had a system that didn't have old coolant and
all sorts of crap in it.

Regardless, it's working nicely in the car.  Pentosin isn't that
expensive when you purchase it from someone other than Blau :-), and
it's only purchased every two years...so what's $10 or so in
difference?  It is, after all, what is recommended for the older
Audis(newer Audis use the red pentosin); I don't think you could go
wrong running it versus Prestone.

If someone is willing to play guinea pig, someone who has a system in
good shape already and is running The Green Stuff, please, give
pentosin a shot and let us know how it turns out.

B
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