expansion bottle - overflow - 912s

[Frequent Flyer]

Hi guys, a while ago i flew and during the climb the overflow bottle did what it's name implied - it overflowed and water (coolant) poured into the cocpit and over the windscreen. Tempratures where normal (a bit hotter than normal but not hot), cht, egt oil temps was all in the green. I immediately landed and let the engine cool down and inspected the coolant level which was maybe a bit to high (close to the full mark on the expansion tank/bottle). i removed some of the coolant until the bottle was about halfway between full and empty) and marked the level with a marker pen, i flew for an half an hour, landed and marked the upper limmit again. Before every flight i checked the level and after every flight i checked the level and found it to be constant (cold and warm). Yesterday, i took off again and climbed to 7000'' @ 5200rpm and maintaining 95-100kph (as per operating handbook)
costantly checking the T & P's - every thing a.ok and al of a sudden - water all over the windscreen and over my feet in the cocpit! returned to the field, carefully watching the temps - every thing stayed normal (in the green), I landed and inspected and the coolant level was lower than my previous mark (obviously) but the bottle still had water in (just below half). The coolant mix is a 50%coolant/50%distilled water mix. any words of wizdom please

[Stephan van Tonder]

Your radiator pressure cap might be faulty. I would start by changing that.

[Morph]

I am having the same problem. Check the radiator cap. It's supposed to be a 1.2 bar. Mine is a 0.9 bar. It is marked on top of the cap

My back right CHT typically runs about 9 deg hotter than the front left. On normal flights the temps are 90 and 99.

On a long climb or running constantly over 4800rpm the temps start climbing. I have had them reach 101 and 110. Even creeping a little over .

When this happens the 0.9bar cap releases the water into the overflow bottle, causing a boil over. It appears the cap is releasing pressure too early.

There is a directive that says we need to replace the cap. the 1.2 bar cap will only release once the CHT exceeds 120deg, which is the max operating temp for CHT.

Running 100% coolant will run hotter as the coolent cannot dissipate the heat fast enough. Under normal circumstances this is fine but with the 0.9 cap it will boil over quicker, due to not being able to cool as efficiently as 50/50 mix.

Aviation Engines sell the caps at R480 ex VAT

BTW I have found I can manage it by reducing throttle if the temps creep up. it means at the moment my Cruising speed is limited to about 80 instead of 90

[Frequent Flyer]

will go and check cap during luch brake and report back

[Frequent Flyer]

r/cap is 1.2 bar. i've concted my analog cht guages again - want to compare cht temps from electronic with analog. still no anwer

[Tumbleweed]

If I fill my 912S reservoir bottle, I get the overflow/white residue spilled over the motor. Always find the radiator full, but the reservoir always almost empty.

[Carel]

Taking a wide long shot here.

Have an intense interest in anything mechanical and always tinkering. Along the way encounter some baffling problems that were eventually solved by exploring all possible causes and eventually solving the problem. Had two engines (one automotive and the other aviation) that displayed similar simptoms. Heat slightly up when the engine is working, boiling water overflowing the expansion tank and the dissapearance of the water from the tank.

Problem was eventually solved, after radiater caps have been replaced, radiaters flushed, etc., by putting the cooling system under pressure for 12 hours. any drop in pressure indicates to leakage, even un-noticed. Check hoses and clamps, if good pressurise again. Should you have a drop in pressure again, gaskets or under/over torqued tops may be the culprit. The leak may be so small that there is no oil/water mix but a heat transfer still occur. The one egine needs the top to be re-torqued, while the other engine needs the top gasket to be replaced as a close to non existance pin prick hole was eventually find in the gasket.

As I said a long shot.

[Frequent Flyer]

Greg - the water being expelled - or the bit that was lying on the expansion bottles cap had a redish / blackish colour to it hopefully not oil in water? will it be the other way around water in oil if it was a gasket?

[Boet]

What kind of aeroplane you flying? The question is relevant as cooling is an issue in some intallations. Let`s take it from there.

[Frequent Flyer]

oom boet, you know the one - its a yellow 'pyp en lap aerie' wat n verry unfortunate 'whoopy - ground loopy' gemaak het hier by kuruman (die stert wiel het ek darm nou onder die knie ) nou net die verdomde vliegtuig wat heeltyd my voete wil was (die water loop binne in die kajuit in en drup op my voete )

n zlin - savage met n 912s

[Morph]

Greg - the water being expelled - or the bit that was lying on the expansion bottles cap had a redish / blackish colour to it hopefully not oil in water? will it be the other way around water in oil if it was a gasket?

Wow Should be luminous green. Defintately worth draining the water system and having a good look

[tandemtod1]

Hi Morph,
Only the cylinder heads on the 912 are liquid cooled so you can't get oil in the coolant by means of a faulty gasket so no worries there. The only way to get water in the oil or visa versa is to have a crack in the head and a hole in the piston at the same time and on yhe same cylinder which I doubt you have or your complaint would be different. The only way for the coolant to overflow the bottle (assuming you have the correct size bottle) is A) The cap is letting off pressure too early ie faulty cap or B) The coolant is simply getting too hot.
Take your cap to a radiator repair shop and they will test it on a pump and will tell you the break pressure. If it checks out OK then you need to look at the airflow over the radiator. If the cap is shot, you can buy a 1,2 kpa cap for a Toyota Corolla for about a quarter of the price. (never done it but this is what I am told)
I have seen this exact same problem with the first of the 912 Cheaters and I believe they increased the size of the radiator to solve it.
Good luck with solving your problem

[Boet]

Corolla radiator cap??? NOPE, only Rattex cap works. The Toyota cap is too short. How do I know? ( I was a Toyota dealer, and thought it would be convenient to grap one off the genuine Toyota spares rack. Hu-uh.....does`nt work..... ) PAY up and look pleasant. Die wet van Transvaal "geld". I think the radiator on your eastern-block wonder may be a little small, OR there might be something amiss with the water pump. ( Spell: VERYVERY expensiv. ). The COLOUR of the water leaking out is not good. Check, and recheck, this could become VERY expensive.

[Frequent Flyer]

ok, today i removed the radiator, flushed the whole cooling system including the radiator and renewed the cooling liquid with castrol all conditions antifreeze - green- (mixed to a ratio of 30%coolant and 70% distilled water - after consulting with the rotax gurus in the big smoke - as it get's really hot here) i said in my previous post that the coolant had a redish tint/colour to it - previous owner used castrol Silica Free coolant - hence the red colour. i had the radiator cap checked and is a ok. i also installed the analog cht guages again (now have digital and analog cht temp) just to make a comparison between the two as i think the digital ones might be reading 10deg lower than the analog- will watch them carefully this afternoon. i have now purged the cooling system and will check the level again before i fly and again after and give some feedback.

[Frequent Flyer]

Ok, here it goes, after flushing the cooling system, and replacing coolant and purging the whole lot, i took off on a test flight yesterday afternoon. OAT was still 30deg plus @ 18h00. took off and flew for about a half an hour, watching the T&P's with a hawk eye - and wala, water in the cocpit, but this time only a little bit. I landed, inspected the overflow tank and it was above the max mark after i shutdown. i let it cool down, checked the level in the over flow bottle again and found the level to be to high and i took out some coolant and just for incase borrowed a presure cap from a friend (also from a rotax 912, not a toyota) - i think this was the problem from the start. left it to cool down and this morning everytthing was a ok, coolant level 100% before flight (on the min line on the bottle) and just under the max line after my 2hr flight this morning and no coolant in the cocpit.

will do some more flying during the weekend and report back.