This article is from the VW Performance FAQ, by with numerous contributions by Jan Vandenbrande others.
A:Redline sells a "wetting" agent calleed "Water Wetter" as
an additive that improves heat transfer. It comes in two
forms solid (discontinued), which contains phosphates,
and liquid w/o phosphates (OK). People who have used it
can't tell any difference under normal driving
conditions, but it does make a difference if the problem
is that hot spots in the cooling system are causing
localized boiling
Under normal street use you will not see any change
because the thermostat is regulating the temp. It's only
when you exceed the capacity of your system and the
thermostat is all the way open that the wetting agent
will have an effect. The wetting agent is supposed to
improve heat transfer by reducing surface tension. This
is important near the head where the coolant my locally
boil. The little gas bubbles however impede heat
transfer, which in turn may lead to knocking and reduced
engine performance. Redline claims it can reduce engine
temp by as much as 30F (depending on the anti-
freeze/water ratio, for a 50% mix it's closer to 10F I
think). The performance shop I bought it from said that
its good insurance when your car is put under heavy duty
(stuck in traffic on a hot day, making a desert run,
autocross).
Another issue is that glycol raises the boiling point,
but reduces heat capacity. With Water Wetter, you can
hopefully use less glycol, resulting in higher heat
capacity. You want to use as little glycol as you can
while still avoiding boiling (and still getting enough
lubrication for the water pump, which glycol provides).
Note: In certain old high mileage cars, the Water Wetter
scavenges out some of the contamination in the cooling
passages and holds them in suspension in a way that
resembles motor oil. The stuff even "feels" like oil.
Redline said this was quite harmless otherwise, and I
shouldn't have any problems with hoses or the like. They
said because it only happens in a few cars, they didn't
feel justified in putting out a warning notice
(especially if it causes owners of cars with REAL
problems to ignore it).
An other alternative described in European Car (Oct 91)
is to use !pure! propylene glycol that has a higher
boiling point than ethylene glycol though worse heat
transfer properties. [borowski@hpspkla.spk.HP.com] The
higher power VW engines have a problem with pinging under
heavy load. This is due to the coolant boiling inside the
head. Coolant vapor is a very poor heat conductor. This
loss of cooling causes hot spots to form on the
combustion chamber side of the head, causing pinging. The
propylene glycol does not boil, and this cools the hot
spots better. Thus, pinging is avoided, and more power is
available if the timing is set to take advantage of the
reduced chance for pinging. The cooling system is NOT
pressurized, but vented to boil residual moisture away
(which lowers the boiling pt). A kit to make the switch
is available from: MECA Cooling Company [See the first
general FAQ for address]
 
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