So glad to hear your system automatically purges air. That's a big safety
advantage, as trapped air in my testing was easily 10 times more significant
than any other factor in the cooling system. It just dominates cooling. Your
system will purge air as your fly. Much less sensitive to many failure modes
that way. Congrats.
I've always been fascinated by failure patterns. This cooling thing is good
example.....when we don't have measures of how close we are to failure. We make
decisions that move the design to the edge of failure. You wouldn't expect
that. Lack of measurements usually result in marginal designs. FWIW
Al has hit the nail on the head - in my
opinion.
I don't even have my RX-8 mounted yet, much less have
any personal experience with the cooling system. But, I've been
monitoring this list for about 10 years and learning a LOT.
. . .I have previously posted that I plan to use the
Ford Contour (about year model 2000) architecture - pressure coolant tank
(fill system through this tanks opening, which is then sealed with the only
pressure cap in the system), mounted so its coolant level (which allows air
space above the coolant, exactly as Al describes) about level with or slightly
higher than the highest point in the system (top of engine). At this
highest point, there is an "air" bleen (very small line) back directly to the
coolant tank (can't figure if it makes any difference if its entrance into the
tank is below or above the coolant level - think it makes no
difference). This purges steam and air, when/if any exists in the
system, so we have only liquid surrounding the engine.
This cooling system is filled by pouring coolant
into the tank - the main line from tank into cooling system is a straight-down
a large pipe to a T at the bottom of the car's radiator, the lowest spot in
the system, so, as system fills with liquid, it forces air out the top,
eventually with fluid coming out the "air bleed" fitting mentioned above and
concurrently filling the "tank". No burping required. And there is
still an appropriate amount of air on top of the coolant in the
tank.
No one has ever found fault with this system as far as
I've seen by watcing this list - but also, no one has ever resonded to my
posts either saying , "Yeah, that's right" or "That is less than optimum
because . . . ". I'm not whining about not getting reinforcement or
validation. But I'm pointing out that it appears most folks flying so
far already have a non-optimum system installed and must not be ready to
comment about a system they don't use. I'd have thought someone would
have at least commented one way or the other.
. . . But to the contrary, the "other" systems continue
to seem to proliferate and all kinds of different expansion tank locations and
construction get shared here.
Nevertheless, I think Al has described the perfect
system.
David Carter
RV-6 (still on canopy frame)
----- Original Message -----
Sent: Monday, March 19, 2007 2:10
PM
Subject: [FlyRotary] Re: water boiling
point
There's one coolant design that's substantially better than the others.
I discovered it when doing severe ground testing...deliberately overheating
my engine.
Three basic requirements:
1) Place your radiator cap and reservoir above engine. The higher the
better. This allows trapped air in system to rise out of the flow and stay
there.
2) Put a 24 psi cap on the system. You can throw away your overflow
stuff. Not needed.
3) Always keep around 2 cups of air under the cap. This is the key
item. It brings a big safety advantage. It allows you to use coolant
pressure to predict well in advance how good your system is doing. It
minimizes pressure. Mine never exceeds 7 psi. But if something goes wrong,
then my pressure rises and I gain boilover protection due to the increase in
system pressure.
If you have compression leak into the cooling system, it shows
immediately as spike in pressure that reaches 24psi. But when all is normal,
you never see pressure above 7 psi. If you have any cooling problem, the
pressure gage will respond quicker than any other sensor.
Sounds like many of you don't have that 2 cups of air. As result,
your coolant pressure regularly reaches 24 psi. Stressing components
(radiator welds actually). It masks compression leaks. Makes it
difficult to predict your safety margin.
Tough to explain this stuff in text, but it's a big improvement in
safety margin. No downside.
To qualify the system, I omit the two cups of air. This causes pressure
to rise to 24 psi. Thus proving all of my welds and connections have safety
margin. Then I add the 2 cups of air and the system never rises above 7
psi unless something goes wrong....whereupon I have extra margin preventing
boilover. Your biggest cooling risk as it cascades and is nearly
irreversible.
On Sun, 18 Mar 2007 11:41:33 -0400 "Tracy Crook" <
lors01@msn.com> writes:
Higher coolant pressure will naturally increase the risk of a leak
due to blown hose, loose clamp, radiator tank failure, etc. As in
many of these matters, it is the builders choice as to which potential
problem is most important.
BTW, I do recommend doing a system pressure test at
annual inspection time or after making any changes. I
intentionally over-pressure the system by 50% by hooking a regulated air
pressure source to the overflow port on the cap fitting.
I could be wrong but the likelihood of a blown rotor housing coolant
seal from coolant pressure is very low. If coolant pressure
causes them to leak there was a problem that needed to be addressed long
before the leak happened. Most coolant seal leaks happen at the
inner seal which normally have to seal combustion chamber pressure.
Even 30 psi coolant pressure is a very tiny fraction of that.
Tracy (still waiting on
Bluemountain)