>-----Original Message-----
>I think have some posts saved from a gin-u-wine Chrysler
>cooling system engineer who explains a lot about the Euro
>specs for antifreeze. If you are interested, contact me
>off-line and I will try to dig them up.
I picked this up on another car list I am on. I found it interesting.
Larry Hoy
-------- Original Message --------
To: miatapower@milewski.org (Miata Turbo/Supercharger list)
>> '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. HOWEVER... 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 Wetter.
Water Wetter has limited to no benefit in a system using a commercial
coolant -- it's simply adding more of something already present in
sufficient quantity.
Another drawback to straight water is that the freeze point and boiling
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
atmospheric 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 live somewhere that gets cold (that would be most of the
country this winter, it seems).
There are two types of base coolant stock available right now: Ethylene
glycol (EG) and propylene glycol (PG). Currently, no engine
manufacturers selling product in the US recommend PG (sold by Arco as
Sierra brand 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 you.
The LD50 (lethal dose in 50% of ingestion cases) for PG is about 4 times
less than EG's LD50, but that's means we're talking along the lines of
16 ounces 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 aren't 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) a few years back when the FTC challenged their
advertising claims and found them lacking in accuracy. Basically, the
less-toxic claim only applies if you pour the stuff straight out of the
bottle and onto the ground. Don't bother with it. And treat *any* used
coolant as low-level hazmat. Small amounts can be disposed of in
sanitary sewer systems, but you're better off making nice with the
operator of the neighborhood quickie lube place, who will be able to
take it off your hands and get it into the recycling 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 phosphate)
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 plan:
life of vehicle) would be a Good Thing. This lead to Organic Acid
Technology coolant (OAT), which is marketed as "DexCool" by GM and has
been factory-fill in their products (except C4 Corvette -- not sure
about C5
Corvette) since 1995. It's the orange or orangy-red stuff. Someone
along 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 certain sealing materials, so it's not a good
idea to convert a green-coolant car over to OAT unless the manufacturer
says it's okay. OAT also has a tendency to stain translucent plastics
in things like overflow bottles and pressurized de-gas bottles with a
funky brown crud. Oh, and OAT from one manufacturer isn't necessarily
compatible with OAT from a different 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 Organic
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 now, too, 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 the 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
better behaved 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
needs put 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
additives, in particular, leave residues on the walls of the various
coolant passages (that's how they work -- the residues coat the base
metal and prevent corrosion), and it's tricky to convert an engine
that's been run with one style of package to use another package and get
the full benefit. Switching from conventional to OAT, for instance,
requires a mild acid flush of the cooling system after removal of the
conventional coolant and before pouring in the OAT if the long-life
corrosion benefits of the OAT coolant is to be realized. Just pouring
the OAT in after draining the conventional won't gain the full measure
of added coolant life the OAT 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.
Jim Crider"
An address at delphi.com
///
/// shop-talk@autox.team.net mailing list
/// To unsubscribe send a plain text message to majordomo@autox.team.net
/// with nothing in it but
///
/// unsubscribe shop-talk
///
///
|