This article describes various problems & solutions with the coolant(water) system.
Potential Cause 1:
A pilot describes the overheating he experienced:
Today, I started up over Inyokern with OAT [outside air temperature] just a bit below 100F and within just a couple minutes the water temperature started to alarm. Air was at 105 / 110 deg C and so was the water! I throttled back to idle, put the nose down and headed back to the airport. I would think that this would result in a stabilized temperature, but it continued to rise, so I shut down.
After landing the coolant reservoir (or tank or bottle) was nearly full. Before takeoff it was at about 20%. An hour after landing it was again down to about 20%. Any thoughts on how to troubleshoot?
Later, he finds his problem:
Pulled the radiator cap and it was dry in there. Put about 300 ml of coolant in to top it off, and another 50 ml or so into the overflow bottle to get it up to 40%.
Started the engine and ran at 4000 rpm until water hit 70 dg C. Shut down and watched the overflow bottle get sucked dry as the system cooled. Attempted to open radiator cap with engine slightly retracted and also fully erect, but always got coolant trying to come out. So raised tail into flight attitude which put the radiator about vertical, and then I could open the cap and added another couple hundred ml to top of the radiator, as well as bringing the overflow bottle up to 35-40%.
Ran the engine again and let the water get to 80 before shutting down to let it cool. This time the overflow appeared to gain just a tiny bit when hot and then it went back to the original level as things cooled, so we figured the system was now full. I had added a total of 620 ml to the system, so it was very dry!
I think my error was in assuming that as long as the overflow was non empty, the engine would not be sucking air. But probably somewhere down at 10-20%, the siphon tube was above the coolant level.
The siphon tube in the overflow bottle (or tank) should reach the bottom and enable the engine to suck the bottle completely empty. As long as the overflow bottle has adequate coolant level, the engine should slowly purge itself of any residual air in the coolant system, blowing out the air during heating and then sucking in coolant during cool down.
Potential Cause 2 (German version below):
During the last few starts, the temperature of the cooling water repeatedly increased. When checking the cooling water level, we found that it was too low.
We refilled both the cooling water of the system and the content of the cooling water expansion tank after every temperature report at a start. But after just two more starts, there was again a lack of coolant in the system and in the expansion tank. The engine compartment was checked after each landing. It was dry. We couldn't explain the loss of coolant and assumed that the cooling water entered the combustion chamber through a seal.
During the annual routine check, I noticed that there was again too little coolant in the expansion tank. An intensive check of the engine compartment revealed that a small spot below the container was damp. However, the subsequent camera inspection of the expansion tank did not reveal any damage. So I removed the rubber hose that connected the cooling system to the overflow tank. This hose was torn, as shown in the pictures. Apparently it was brittle due to aging. The reason why no cooling water could be found in the engine-bay was that it dripped onto the manifold and immediately evaporated.
The rubber hose was replaced with a petrol hose that had the same inner diameter. We assume that the replacement hose will last longer thanks to the fabric insert. I recommend checking the old rubber hose and replacing it if cracked as part of the annual maintenance.
NOTE: see the images below of the hose
Während der letzten Starts kam es immer wieder zu einer Temperaturerhöhung des Kühlwassers. Bei der Kontrolle des Kühlwasserstandes stellten wir fest, dass er zu gering war.
Wir füllten nach jeder Temperaturmeldung bei einem Start sowohl das Kühlwasser des Systems als auch den Inhalt des Kühlwasserausgleichsbehälters nach. Aber bereits nach zwei weiteren Starts fehlte wieder Kühlflüssigkeit im System und im Ausgleichsbehälter.
Der Motorraum wurde jeweils nach der Landung kontrolliert. Er war trocken. Wir konnten uns den Kühlmittelverlust nicht erklären und vermuteten, dass das Kühlwasser durch eine Dichtng in den Brennraum eintrat.
Bei der jährlichen Routinekontrolle stellte ich fest, dass sich wieder zu wenig Kühlflüssigkeit im Ausgleichsbehälter befand. Eine intensive Kontrolle des Motorraums ergab, dass eine kleine Stelle unterhalb des Behälters feucht war. Die anschließende Kamerainspektion des Ausgleichsbehälters ergab jedoch keine Beschädigung. Deshalb entfernte ich den Gummischlauch, der das Kühlsystem mit dem Überlaufbehälter verband. Dieser Schlauch war gerissen, wir die Bilder zeigen. Offensichtlich war er durch Alterung versprödet.
Der Gummischlauch wurde durch einen Benzinschlauch ersetzt, der den gleichen Innendurchmesser hatte. Wir gehen davon aus, dass der Ersatzschlauch durch die Gewebeeinlage länger halten wird. Ich empfehle, im Rahmen der jährlichen Wartung den alten Gummischlauch zu überprüfen und bei Rissbildung zu ersetzen.
