Air bubbles continuously streaming through the engine coolant system

[sol...@bigpond.com]

From G.Rau.

I have an Arcus Sn. 67 VH ZBX located at Gawler South Australia.

 

I have seen air bubbles streaming up the clear plastic tube alongside the header tank.

The header tank is full of coolant but the bubbles seem to come and go.

The water temperature seems normal and the fluid level does not change in the Header tank.

When this happened at the launch point an observer suggested raising the tail of the aircraft till the nose wheel touched the ground

To check if there was an airlock located in the water pump.

This operation resulted in several bubbles greater than 1.5 cms evacuating up the clear plastic hose while the pump was still operating

and the cooling system still under pressure.

What I don’t understand is changing the fore and aft attitude of the aircraft can influence the water pump.

Can the water pump cavitate as a result of this?

 

Who else has noticed air bubbles come and go like this?

  

[Jorgen Thomsen]

The amount of bubbles will diminish over time.

I have experienced cavity in the water pump after a complete refill of coolant. I got warning of too low current to the water pump.
I could get the cavity to disappear by lowering the engine into the bay, and turn on the water pump by opening the safety cover to the emergency  switch.

Kindly
Jorgen #61

[Daniel GUEDON]

I just had this problem after a coolant replacement, solved by applying Jorgen's tip.

Now I still have coolant exhausting via the exhaust tube when engine heats up, like if there would be coolant in excess, which there is not.

I had a similar issue in the past on a DG808, solved by replacing the coolant radiator cap.

Then I'll try it there as well, but curently I am not in reach of the glider to check the cap reference

Anyone having the commercial reference of this cap ?

Thanks

Daniel

[Arcusdriver Andreas]

Too many air bubbles in the system may well affect the cooling performance , i.e. you may see the temp indication rising above normal !

Air bubbles are produced by too low coolant level which allows air to be sucked in the outlet port of the cooler (right hand side, thick black hose). The bubbles go through all the engine (and of course with adverse effect on cooling performance) and become visible only in the clear tube part when returning and entering in the cooler.

This is avoided by ensuring that the outlet port opening is fully immersed in coolant liquid ! So fill up to the very top until coolant in excess will leave via the spillage tube. Before each engine start I check that no bubbles are visible in the clear tube left hand side.

With engine retracted I did not notice that liquid left the system.

Have nice flight, best regards

Andreas