Zenith Aircraft Builders and Flyers
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Still Working On A Root Cause
We are still trying to figure why exactly all the coolant came out. The best hypothesis is an airlock developed in the system and forced the coolant out.
That still leaves us wondering why the airlock started in the first place.
Once piece of the puzzle has been figured out, which sadly creates a new question. The bottle failed due to exhaust heat. We were seeing EGTs close to the yellow\warning zone before the failure. The portion of the bottle that melted was the portion closest to the exhaust system.
This also brings up the question of why the EGTs were higher than normal....
Comment
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Comment by Michael Sipman on January 11, 2013 at 9:32pm
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Bob, is correct, there should not be any air in the system, the overflow bottle is only to allow for expansion, this is why the radiator cap only lets fluid out of the system at the manufacturers specification. which can be drawn back in as the engine cools. The caps set pressure also increases the temperature at which the fluid will boil.
The problem had to be leak within the system prior to the overflow bottle.
The fact that the fluid can leave the system and John only saw a slight increase in oil and CHT temps is a concern.
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Comment by Chris Aysen on January 11, 2013 at 8:45am
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I back Bob's explanation because I experienced the problem first hand. After 3 flights I noticed the bottle full of coolant. Changed the tank cap releveled coolant started working properly again.
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Comment by Bob McDonald on January 11, 2013 at 7:38am
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Once the coolant was blown out of the overflow bottle "it melted". The coolant level in the bottle transfers just enough heat to prevent it melting. It is designed to always have a level of coolant present and unless the coolant collector tank rad cap "opens to relive for pressure" it normally would only get air bubbles that worked out of the system when hot... and as the engine cools the vacuum left by the expelled air is replaced by sucking coolant from the over flow bottle. The concept is that only coolant is in the engine not air + coolant. Was the coolant bottle level low enough to allow the cooling engine to suck air?
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John, i have worked in the automotive industry for 40 years, its a common problem that occurs when the coolant is lost, the temp sensor has nothing to sense as the fluid has gone, many vehicles utilise coolant level sensors and flow sensors to identify when this problem occurs, hope this assists you in preventing the problem occurring again.
cheers Mike
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