"Schertz, William W." wrote:
Paul,
I have been following the Perry Mick saga re the cooling loss, and I am
interpreting things a little differently. My interpretation comes from some
cooling system failures in automobiles that I have had, and the description
of Perry's incident.
1. I had a Mercedes (1970 model) that had a slow coolant leak through a
gradually failing water pump, and a 1984 Caravan that had a head gasket fail
that leaked (slowly) into the coolant loop. The behavior of both of these
had some similarities with Perry's behavior,
2. Both cases resulted in low coolant level in the system, but no
overheating on the highway, moving at a good engine speed. However, when I
then slowed up at a stop sign, the temperature would IMMEDIATELY start to
rise. Slipping the car into neutral and increasing the rpm would bring the
temps back down quickly. I would notice the behavior on the temperature
gauge, and then refill with coolant right away, so I never took it to
catastrophic failure.
My analysis of what was going on is
* When the coolant gets low, the water pump no longer had sufficient head to
circulate the fluid when at idle rpm. At highway speed, or goosing the
engine gave enough head to get the fluid circulating again.
* In the case of the Mercedes, the low coolant was the result of a slow
leak, which resulted in the overflow bottle gradually going down until it
could not replace the fluid on cool-down. Then the behavior would start
again.
* In the case of the Caravan, the exhaust gas would displace fluid back into
the overflow bottle, until a path for the leaking combustion products could
reach the overflow vent, then it would bubble out into the overflow tank.
Cooling and refilling the system had a very short time of effectiveness,
since it just displaced the coolant on the next cycle.
Perry indicated that the engine overheated after landing, not during the
flight. This would be consistent with the above behavior, because after the
engine was worked hard, and then the coolant stopped flowing, all that
residual heat in the metal would be dumped to the remaining coolant and
cause it to overheat very quickly.
As to the use of the tire schraeder valve, I would strongly doubt its
utility from a reliability standpoint in long term use. Designed for an air
use, at close to AMBIENT temperature, I would worry about the rubber
compounds durability and life time exposed to 180F and moisture. It could
easily become a NEW weak point and source of failure.
My checklist of lessons learned from this incident include:
1. Pay attention to the temp gauge, become familiar with "normal" and when
it behaves differently find out why,
2. Inspect for coolant leaks regularly, pressure test system with every oil
change
3. Use only high quality connections, with approved fittings
4. Check the tension bolts (visual) with every oil change
5. I am against "emergency core cooling" from a complexity and weight
penalty. I think it might cause as many problems as it solves. It will
only help in the case of a slow leak, and then for a short time only. If
you have a catastrophic failure of a hose/joint, the show is over even with
the complex spray system. Better to inspect and test periodically.
Bill Schertz
I think we can all agree. A few bucks on the finest plumbing money can buy
is cheap insurance. Perry pointed out that Summit Racing has Aeroquip AQP
AN-16 hose and fittings at moderate prices. I think this is about one inch
ID which will do the job if a bit small. Will do if you don't want to weld
up 1-3/8 inch aluminum tubes with wiggins couplings.
http://www.summitracing.com
I know Perry is now convinced this is the way to go. We will be pipe taping
his block in a few places for AN plumbing all the way.
Paul Lamar
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