|
Re: [FlyRotary] water boiling point
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)
|