Posted for "David Carter" <dcarter@datarecall.net>:

I've been thinking of recent posts to this thread all day long driving home
today from Birmingham, AL to Nederland, TX, trying to do a mental design of
my 13B coolant system, factoring in some of the details that I've been
reading about and thinking shallowly about for several years.

First, this is obviously an important thread and some good "insights" ('a
Ha!'s) are coming together from different previously unknown-to-be-related
facts (classic definition of "insight" in flt instructor manual).  E.g., 1)
"runs a little cooler for 1 flight when I top off the system, but goes back
to normal 5 to 10 degrees hotter after that initial "topped off" flight
(caused possibly by tiny bit of steam forming during takeoff & climb that
displaces more coolant than we'd expect from a simple increase of coolant
temp from "cold" to "185 degrees" - the steam will condense back to liquid,
but not until AFTER  forcing out some coolant from a "too small" expansion
tank or bottle - which is the variable between systems that consistently
lose coolant or don't.  Steam volume is about 1000 times the size of the
liquid volume before it flashes going by the combustion chamber.  So, if
lose 2 fluid ounces of coolant, maybe got 2 oz of steam volume, which would
come from 2/1000 fl oz of liquid water - NOT MUCH!)
   E.g, 2)  Bill's most recent:  "I always get a bit of air, maybe just the
volume of the vent tube." - I thought about that one most of all today, then
reached home and found Bill's post:  If all the vent tubes to-from an
expansion tank don't run UPHILL to the tank and enter that tank below liquid
level, then they are running DOWNHILL and therefore can/will drain out and
fill with air while everything is going along 'apparently nicely' during
flight.  Then, we when shut down, we get that "tube volume" of air sucked
into the "closed, supposed-to-be-totally-fluid-system" before the liquid
starts being sucked in.  Then, as another poster said, you have a bit of
air, not steam that will re-condense, continuously circulating (and
increasing perhaps after every flight/shyutdown)  probably as tiny bubbles,
but which nonetheless cut the density and heat absorbing capacity of the
coolant - something like 4% change was roughly calculated in that e-mail.
Not much, but in the ball park for the 5 to 10 degree increase in temp
noted.

I recently had an oppurtunity to help a fellow diagnose a cooling problem
with his 1995 or '98? Ford Taurus.  A visual examination of the entire
system revealed a couple of  things I'd never seen before, but which were
VERY GOOD to emulate:  1)  The expansion tank was pressurized - had a big
lock-on cap that had the 12-15 psi pressure relief valve right in the
center.  Don't remember if it had a vent hose to anything - think not.  2)
The connection of this tank to the radiator was different from the "std"
setups I'd seen on all other cars I own or have owned, which were a simple
small rubber hose running from a stem off the radiator pressure cap's neck
where coolant blowby (above the 15psi cap rating)  would go to the
non-pressurized, translucent expansion tank, until shutdown, at which time
the coolant would be sucked back into the radiator, keeping it full.  This
Taurus system was different:  It had 3  tubes - 1st from the top corner of
the radiator, which lets air be forced out when filling the coolant system,
2nd from top part of engine head - highest point - which lets air be forced
out when filling the coolant system, and last of all, it had a bigger tube
that went straight down out of the bottom of the expansion tank to a T
fitting on the radiator hose at the bottom of the radiator.  This "down
tube" was simply for filling the radiator and engine block "from the
bottom", with the other two previously mentioned allowing air to be
displaced/expelled as the liquid level rose in the radiator and engine block
& head.
     Good system - makes more sense than anything I've seen.  Both the air
vent hoses ran level or uphill into the expansion tank and entered below the
"cold" water level.

Summary:  I figure I'm going to get one of those Taurus tanks, measure
volume ABOVE the "Cold" level, hope it is 1 1/4 qts to match the emperical
data that says a 1 qt tank is too small for what is happening on Tracy's and
some other systems ("it burped 2 oz out of the expansion tank into the test
bottle or whatever Tracy attached to the overflow port of his expansion
tank").  Then I'll make sure there is an additional fitting on each of my
GM/Harrison air conditioner core "radiators" for air vent tubes that go UP
slightly and T into the "fill"/"down" line so all air will be expelled from
the radiators and go up into and out of the expansion tank while I'm filling
the system with the pressure cap off the exp tank -  when I fill the system;
and then the "fill line/down tube"  will T into the water hose to the water
pump.  Last, I'll have an air vent line from the front/high end of the 13B
block - in looking at Dave Atkins' engine a couple of years ago, I think I
noted there are plugged holes available at either end of engine for that
"top air vent" line to run to the expansion tank.  Finally, to keep all
lines going UP, I'll mount the pressurized expansion tank up fwd of the
engine in vicinity of PSRU so its "cold" coolant level will be slightly
above the top of engine block.  Hope that doesn't require a bubble in my
RV-6 engine cowling.

David Carter