Cooling System Info
'Jim Crider wrote'>>
"Here's a response from someone who designs vehicle cooling
systems for a living ......
(that would be me):
Strictly looking at the heat transfer coefficient, straight water is the way to go.
straight water has its problems, notably a lack of certain
additives that prevent cavitation of the water pump at high
speeds, corrosion of the various metal bits present in all engine
cooling systems, surfactants to lower the surface tension of the
coolant (allowing it to "wet" the surfaces of the
coolant passages better) and anti-foaming agents to keep the
surfactants from making big bubbles.
All these are present in antifreeze/coolant. The
surfactants and anti-foaming agents are present in Redline Water
Water Wetter has limited to no benefit in a system using a
coolant -- it's simply adding more of something already present
Another drawback to straight water is that the freeze point and
points are closer together than a mix of coolant and water.
A 50/50 mix of
ethylene glycol and water will boil at 220F at atmospheric
pressure at sea
level, compare with 212F for straight water. A pressure
cap, by the way,
adds about 3 degrees F to the boiling point per psi above
pressure. And of course, water freezes at 32F, while a 50/50
EG/W mix will
freeze at about -35F. This of course is useful should you
that gets cold (that would be most of the country this winter, it
There are two types of base coolant stock available right now:
glycol (EG) and propylene glycol (PG). Currently, no engine
selling product in the US recommend PG (sold by Arco as Sierra
coolant), most caution against it (check your owner's guide).
PG has a
higher boiling point than EG (straight), but has a lower heat-transfer
coefficient. EG coolants also come in several flavors,
depending on the
additive package (more below).
BTW, PG isn't truly non-toxic.
It's LESS toxic
than EG, but PG coolant
contains various and sundry additives that aren't really good for
LD50 (lethal dose in 50% of ingestion cases) for PG is about 4
than EG's LD50, but that's means we're talking along the lines of
instead of 4 ounces for a small kid or large dog. And once
it's been in a
cooling system, it's picked up contaminants (metals, etc.) that
terribly good for you. Arco got in a fair bit of trouble
and had to
re-label Sierra (including all the stuff already on store shelves)
years back when the FTC challenged their advertising claims and
lacking in accuracy. Basically, the less-toxic claim only
applies if you
pour the stuff straight out of the bottle and onto the ground.
bother with it. And treat *any* used coolant as low-level
amounts can be disposed of in sanitary sewer systems, but you're
making nice with the operator of the neighborhood quickie lube
will be able to take it off your hands and get it into the
stream, sometimes for a nominal fee. You're already talking
to him about
your used motor oil anyway, right?
The green-dyed EG "conventional" coolant we all know
and love has an
additive package based around a silicate (and sometimes also
based anti-corrosion additive. It's well-established and
does a good job.
It can go 5 years/50K miles without worry.
A few years ago, someone thought a long-life coolant (original
of vehicle) would be a Good Thing. This lead to Organic
coolant (OAT), which is marketed as "DexCool" by GM and
factory-fill in their products (except C4 Corvette -- not sure
Corvette) since 1995. It's the orange or orangy-red stuff.
the line decided the word "acid" was a Bad Thing to try
to sell, so OAT was
recursively changed to Organic Additive Technology. It can
go 5 years/100K
or 150K miles -- provided it's not mixed with other coolant.
OAT has less
cavitation resistance than silicate-based coolant, and can attack
sealing materials, so it's not a good idea to convert a green-coolant
over to OAT unless the manufacturer says it's okay. OAT
also has a
tendency to stain translucent plastics in things like overflow
pressurized de-gas bottles with a funky brown crud. Oh, and
OAT from one
manufacturer isn't necessarily compatible with OAT from a
manufacturer. Texaco is GM's OEM supplier and is licensed
to use GM's
"DexCool" trademark on their aftermarket packaging.
I'm not aware of any
other company being licensed to do so.
Many European automakers use a hybrid of OAT -- HOAT (Hybrid
Additive Technology -- clever, huh?), which is the OAT package
with a small
amount of silicates added to increase the cavitation resistance
and make it
less aggressive against those seals and gaskets. This is
often pale yellow
in color. DaimlerChrysler is using it in several car lines
notably the LH sedans and the new minivans (It's possible the
Sebring/Stratus twins now use it -- I don't have that handy at
present). This stuff seems to offer pretty much the best of
both worlds --
it's not quite as long-lived as straight OAT, but it is much
in operation than OAT, much like conventional coolant.
Note that these three different additive packages are not really
cross-compatible. No, they won't eat the insides of your
radiator if you
mix a little of one in with another in a pinch, but you'll be
better to get
the system flushed out and a fresh mix of 50/50 whatever your car
back into it.
In my own cars, I run a 50/50 EG/W coolant mix. I happen to
own cars that
take conventional coolant, but if I owned a car that came with
OAT or HOAT
from the factory, I'd likely stay with it. The anti-corrosion
in particular, leave residues on the walls of the various coolant
(that's how they work -- the residues coat the base metal and
corrosion), and it's tricky to convert an engine that's been run
style of package to use another package and get the full benefit.
Switching from conventional to OAT, for instance, requires a mild
flush of the cooling system after removal of the conventional
before pouring in the OAT if the long-life corrosion benefits of
coolant is to be realized. Just pouring the OAT in after
conventional won't gain the full measure of added coolant life
marketers (notably Texaco) like to use as selling points.
Radiator caps are a whole topic unto themselves. Ask me
about them another
time -- my lunch hour is over and I gotta get back to work. :)
Hope this is helpful.