Rotax 912UL coolant liquid

by Przemysław Wiśniewski in 912 / 914 Technical Questions 7 years ago

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Re: Rotax 912UL coolant liquid

by Bill Hertzel » 6 years ago

Bill Hertzel

13 1.95k 7.97k

Roger is correct!
The system will take care of itself.

There was no point in filling the hose at the first fill because the very first time the coolant came up to temperature it out-gassed all the dissolved air in the water.
It is equivalent to a soda warming up and going flat. Lots of air bubbles.
The first thing that happened was that the radiator "Burbed" the dissolved air and blew all the coolant out of your carefully pre-filled hose.

Water expands about 3% going from room temperature to just below boiling.
Because the radiator is 100% filled, This causes about 4oz per gallon to dump into the expansion/overflow tank.
This refilled your overflow hose without you ever seeing it happen.

When the engine cooled after shutdown, the contracting water pulled coolant from the expansion bottle maintaining the 100% filled condition.
This cycle happens everytime the engine is run and the reason you do Not want to completely fill the expansion/overflow bottle.
A 1/3 to 1/2 full expansion/overflow bottle on a cold engine allows room for the bottle to not actually overflow when the engine heats up.

The system takes care of itself.

Bill Hertzel
Rotax 912is
North Ridgeville, OH, USA
Clicking the "Thank You" is Always Appreciated by Everyone.

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Re: Rotax 912UL coolant liquid

by William Campbell » 6 years ago

William Campbell

15 25 43

I agree with what is said about the hose being filled by itself upon a few heat cool cycles of the engine. The part I disagree with is opening the radiator cap to check the coolant before each flight, as removing it will allow all the coolant in the hose to return to the overflow tank. By having a clear overflow line I can visually see the system is full to the high or low level I have marked on my overflow tank with a sharpie. Also by having the system remain closed with the overflow line full should I develop a pin hole leak while flying the water will be immediately drawn from the overflow tank back to the engine and hopefully I would be back on the ground before all the water is drawn back into the engine and out the leak.

Other insight into the clear hose to the overflow tank. I was continually seeing air bubbles in the hose before and after each flight. That is where I attempted to manually fill the hose by raising the overflow tank to back fill the hose and fill the reservoir before replacing the radiator cap. I was very successful in doing this but after a few flights I began getting air bubbles in the clear line to the overflow tank. The fix for it was a new radiator cap. Now the line is always full and it is my belief that I can assume the capped reservoir is full thus eliminating the need to remove the radiator cap before each flight as long as the fluid levels remain constant in my overflow tank.

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Re: Rotax 912UL coolant liquid

by Roger Lee » 6 years ago

Roger Lee

127 5.21k 4.79k

I never recommend removing the expansion tank cap each flight. You’ll just wear it out. I do remove them at annual to look.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

Thank you said by: William Campbell

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Re: Rotax 912UL coolant liquid

by William Campbell » 6 years ago

William Campbell

15 25 43

I appreciate your help and comments Roger. I agree with not removing the cap plus they are about $80 to replace. It is just another thing to put back on incorrectly when you are distracted during a pre-flight check. I always make sure the cap is seated properly with both ears are under the edge of the reservoir and fully turned to the stop. There is no room for error here plus we are hitting the 100F here in Fresno now.

Bill Campbell
Central Valley SportPlanes - Fresno, CA.

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Re: Rotax 912UL coolant liquid

by Capt. Siva, » 5 years ago

Capt. Siva,

25 266 738

Reference S.I, 914-019R10 at para 4.3 mentioned that water less coolant i.e EVANS is not permited for engine 912-915-914?

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Rotax 912UL coolant liquid

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