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pwmac(at)sisna.com
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 Posted: Mon Sep 04, 2006 3:00 pm Post subject: 912UL Initial Engine Test Run |
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Hugh,
I have not followed closely. What steps did you
take to bleed the air out of the coolant system?
Its pretty common to have a big air pocket that
is difficult to dislodge. If there is a pocket of
air then overflow after shutdown would be
expected as would excessive temps. I usually use
a hand held vacuum pump for a bleed task.
BTW, I would recommend spending the extra $$ and
put in the proper coolant. This will elevate the
boiling point and the max allowable temp. The
Rotax bulletin tells you which formulation to
buy. A side benefit would be the low pressure in
the system achieved with the new low pressure cap
Rotax cap. This will allow longer life for the
various coolant system seals. The only drawback is cost of coolant.
Regards, Paul
=================
At 04:17 PM 9/4/2006, you wrote:
[quote]
McKay III" <hgmckay(at)bellsouth.net>
Thom/Gilles:
I have followed your dialogue with great interest, and it has helped me
immensely. I have no experience with this engine, so I was alarmed when I
saw the CHT continuing to rise. I was even more alarmed when I shut down,
and heard the coolant boiling in the overflow bottle. I still don't know why
this happened. There is no question that the engine was not being cooled
properly, the question is why? It may have been a combination of existing
circumstances (i.e. static engine run, no horizontal movement of plane,
tarmac temp 88 degrees+, engine fully cowled with spinner, horizontal
radiator, and length of operation). I do know that with the spinner on, the
91/2 inch diameter spinner flange eats up most of the free area for air to
enter the engine compartment. In fact there is only 18 square inches of free
opening left for air to enter the engine compartment. This may be fine with
the plane traveling at, say 90 mph, but maybe not with the plane sitting on
the ground for 10 to 15 minutes in 88° F. I don't know, but certainly I
would think the plane designers would design for this condition. What free
opening does Rotax require on fully cowled engines?
Since this was the initial engine start, I am going to call Lockwood Green
tomorrow and explain every thing that happened to them and get their
opinion. I'll keep both of you informed as to what they say. Again, thank
you for your advice, counsel, experience, and knowledge.
Hugh
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hgmckay
Joined: 23 May 2006
Posts: 397
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| Posted: Mon Sep 04, 2006 3:28 pm Post subject: 912UL Initial Engine Test Run |
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Paul:
I did not bleed air out of the system. I did not know I had too! There is no
information in the Rotax operators manual addressing cooling system "air
pockets"! This is all news to me! Where is this "air pocket" supposed to
form, and where and how do you remove it with a "hand held" vacuum pump?
Hugh
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daveaustin2(at)can.rogers
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| Posted: Mon Sep 04, 2006 4:03 pm Post subject: 912UL Initial Engine Test Run |
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Been watching this thread with interest as I had a boil during a flight back
in the a/c early days.
The key to the situation is that the coolant has boiled. When it does, the
vapour no longer carries the heat away and the local hotspot rapidly
increases in temperature well beyond limits for the aluminium. That causes
distortion of the overheated area.
I was using a 80% antifreeze mix at the time as instructed back then, and
the heat transfer properties at that mixture is lower than at the usual 50%
mix. Changed to 50% and the boiling never occurred again.
I'd do a careful compression test and coolant leak test at pressure. Make
sure coolant is not getting into the crankcase and into the oil. If no
problems, run it again. Make sure the cap is giving you the full pressure.
Dave Austin 601HDS - 912, Spitfire Mk VIII
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bjohnson(at)satx.rr.com
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| Posted: Mon Sep 04, 2006 8:35 pm Post subject: 912UL Initial Engine Test Run |
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Beware of using the evans coolant in a system (aircraft) not specifically
designed for it. I ended up in a baaaad situation with vapor lock (with
100LL!!! And insulated fuel lines) after switching to evans. Evans, while
not boiling until well over 300F, also does not cool as well. You WILL see
at least 30F increase in normal operating temps with the evans coolant.
-Bruce
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pwmac(at)sisna.com
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| Posted: Tue Sep 05, 2006 6:02 am Post subject: 912UL Initial Engine Test Run |
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Normal procedure when a system has no high point
bleed or when one suspects an air pocket, which
is 100% of the time for me. Any mechanic would do
this for brakes, power steering and coolant.
Based on experience some engine coolant systems
do not need it. In the case of the Rotax I would
do it just to be sure. Any engine has air pockets
after the first fill and some will self purge.
Harbor Freight has a cheap hand operated vac
pump. Get a rubber stopper from the hardware
store drill a hole and put it in the filler and
start sucking. Do this until the vacuum holds
steady. You might have to get another pressure
cap and drill a hole in it to get a proper seal.
Study the coolant pipes to see what you have done
that may have caused a place where the bubble
could form. But, who cares just bleed it to be sure.
At 05:27 PM 9/4/2006, you wrote:
[quote]
McKay III" <hgmckay(at)bellsouth.net>
Paul:
I did not bleed air out of the system. I did not know I had too! There is no
information in the Rotax operators manual addressing cooling system "air
pockets"! This is all news to me! Where is this "air pocket" supposed to
form, and where and how do you remove it with a "hand held" vacuum pump?
Hugh
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