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Thruster88

Why engines can rust

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This pic was taken just after removing the rocker cover. The engine had a performance ground run 24 hours prior before a 100 hourly inspection.

Yes those are water droplets, my advice, don't start your engine unless you are going flying.

  

20190712_082839.jpg
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It takes at least 30 minutes for an engine to reach its correct operating temperature and any water vapour will take even longer to dissipate through the breather system. Short engine runs especially when humidity is high and diurnal temperature variation is also high can cause water from vapour to condense as droplets and eventually mix with oil which will become opaque and eventually quite milky. As soon as this becomes evident change the oil and your engine running habits.

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You probably won't start to get the water out of your engine until the oil gets above 85 degrees C (where you measure it, and it will have to be hotter in other places. to do the job).

 The water doesn't come from the atmosphere. The hydrogen in the fuel forms water with the oxygen that burns it.  (H20)

 How much?  Petrol is CnH2n+2 = C8 H18 atomic weight total 96+18 = 114  the hydrogen H18 plus O 10 has an atomic wt total of 18+120 =140 so you get a larger wt of water than petrol as a result 70/57. the water in the engine comes from burning the fuel, and there's plenty of it. . Most goes out the exhaust but some goes past the rings or your exhaust valve guides. It's also got nasties from the fuel additives and impurities often forming acids.

   Just imagine IF that engine had not been run for a month or so afterwards It would be a corroding mess invisible to your eyes. People fly a bit and leave their precious plane in front of the clubhouse and as the sun sets, fire it up and taxi to the hangar. Get the picture?

   They also give it a good 10 minute run with a few revs on, every 3 or 6 weeks. That's probably doing more harm than good.. No wonder some of this stuff plays up. Nev

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Posted (edited)

An extra precaution is to put a bung in the exhaust pipe and a cover over the air intake when leaving the aircraft for more than a day. By closing up these openings you prevent air movement in and out of the engine due to atmospheric pressure changes as weather systems move through. If you use this method, don't forget to attach long red streamers to the bung and cover so that you remember to remove them during pre-flight.

 

You have to remember that in a four cylinder engine, one of the inlet valves and one of the exhaust valves will be open. So two combustion chambers will be exposed to moisture drawn in by atmospheric pressure changes.  For long-term inactivity a wise owner will remove the plugs and squirt some rust inhibitor into each cylinder; replace the plugs and fit bungs.

 

That now opens the discussion into preventing water build-up in fuel metal fuel tanks.

Edited by old man emu

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Good oil will cope with huge amounts of water. The real worry is the dry exposed cylinder bores that will rust in a few days.

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Sooooo! the take home message is:

 

Fly often   - For at least 30 minutes - Get your engine up to full operating temperature (a nice long cruise climb is a good way to go) - Change your oil at the prescribed intervals (or more frequently )  - You could try exhaust &  inlet bungs as well - All agreed ??

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Posted (edited)

The clever and wise old mechanics in the U.S., used to dealing with weather extremes, would insert a lit light globe into closed toolboxes left in the shop, with the heat from the light globe being enough to drive out moisture, and prevent their high grade steel tools from rusting.

 

It would be useful to devise a similar, low-heat source arrangement to install into engines, to drive out moisture.

Not so sure that inserting a lit light globe into a fuel tank would be advisable, the risk of a spark would overwhelm the heating-to-drive-off-the-moisture advantage.

Edited by onetrack
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Posted (edited)

Air flow through a shut down engine is virtually NIL You would need two valves open in any particular cylinder for it to be possible and that's about a  50 degree window  with one "best" spot and gas doesn't flow without a pressure differential. WD up the exhaust and a plug doesn't do any harm Wait about 15 minutes for it to go  there and stay, Earlier and it might easily start burning, as the interior baffles get a lot hotter than the outside skin.  The risk with this type of corrosion is stuck valves, bores corroded when they are steel and to a lesser extent iron, valve springs pitted and more likely to break and general sludge build up. and piston rings jamming. in the grooves. Clean new oil is great but contaminated oil  combined with even small amounts of  water with acids will corrode all engine parts pretty much unless they are surface treated to reduce it.  There's very little oil stays on the surface of the bores with the savage oil rings they use these days. Nev

Edited by facthunter
corrections

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3 hours ago, old man emu said:

An extra precaution is to put a bung in the exhaust pipe and a cover over the air intake when leaving the aircraft for more than a day. By closing up these openings you prevent air movement in and out of the engine due to atmospheric pressure changes as weather systems move through.

 

That now opens the discussion into preventing water build-up in fuel metal fuel tanks.

The carb heat selector box is not sealed well enough on any aircraft to stop the engine breathing due to pressure changes. This is a not an issue.  As Facthunter  says the moisture comes from combustion. 

 

Metal fuel tanks, the musketeer has 110 l per side and I usually keep them about half full, so plenty of room for condensation.

I have never drained a single drop of water except after washing or rain. The tanks drain water perfectly so I guess I am saying that's not an issue either. The tanks are pristine inside after 56 years with only a bit of corrosion on the steel parts of the caps. 

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The Lycoming engines are prone to camshaft corrosion if not run regularly. I would assume Jabiru would be the same and probably Rotax if the camshaft is above the crankshaft.

I have never had water in my fuel tanks, but I do try to keep them pretty full. I have seen engines with the dipsticks showing white foamy liquid instead of oil, due to water in the oil. Luckily not in aero engines.

Another way to damage your engine is to turn it over to supposedly spread the oil around. It doesn't get enough turns to produce oil flow from the bearings, but it is enough to scrape the oil off the camshaft and cam followers.

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 A good shaped bottom on the fuel tank  would make it all collect there. Fuel tanks are sometimes WET (Part of the wing). Back a million years ago we used to fill the tanks to the top each night to prevent condensation. For many practical reasons that's not always possible. Drain frequently and have the plane level at the time.  Nev

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36 minutes ago, facthunter said:

 A good shaped bottom on the fuel tank  would make it all collect there. Fuel tanks are sometimes WET (Part of the wing). Back a million years ago we used to fill the tanks to the top each night to prevent condensation. For many practical reasons that's not always possible. Drain frequently and have the plane level at the time.  Nev

I am also in favour of a "Good Shaped Bottom" possibly for other reasons.

 

On another unrelated note: I was trained to always fill the tractor/header/ whatever tank  & "grease up"  (works better on warm bearings) after work, for the reasons you have mentioned and to minimise the work load the next morning - a good practice if aircraft is being flown very frequently.

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 I thought "someone" would respond. Congrats. You win the prize.  Nev

Edited by facthunter
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Home made “engine saver” could be a good solution for high humidity areas.  Fish tank air pump plumped into a chemical dehydrator to pump dry air into the crankcase via the oil filler cap.

 

https://www.aircraftspruce.com/catalog/eppages/engsaver.php

Edited by snarf007

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 We used dry Nitrogen to get the humidity caused condensation out of the magnetos of DC4's in the tropics, otherwise the mag drops would be out of this world. Nev

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On 09/08/2019 at 10:23 AM, facthunter said:

You probably won't start to get the water out of your engine until the oil gets above 85 degrees C (where you measure it, and it will have to be hotter in other places. to do the job).

 The water doesn't come from the atmosphere. The hydrogen in the fuel forms water with the oxygen that burns it.  (H20)

 How much?  Petrol is CnH2n+2 = C8 H18 atomic weight total 96+18 = 114  the hydrogen H18 plus O 10 has an atomic wt total of 18+120 =140 so you get a larger wt of water than petrol as a result 70/57. the water in the engine comes from burning the fuel, and there's plenty of it. . Most goes out the exhaust but some goes past the rings or your exhaust valve guides. It's also got nasties from the fuel additives and impurities often forming acids.

   Just imagine IF that engine had not been run for a month or so afterwards It would be a corroding mess invisible to your eyes. People fly a bit and leave their precious plane in front of the clubhouse and as the sun sets, fire it up and taxi to the hangar. Get the picture?

   They also give it a good 10 minute run with a few revs on, every 3 or 6 weeks. That's probably doing more harm than good.. No wonder some of this stuff plays up. Nev

The water in that rocker cover would be from the atmosphere 

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On 09/08/2019 at 6:50 PM, facthunter said:

 A good shaped bottom on the fuel tank  would make it all collect there. Fuel tanks are sometimes WET (Part of the wing). Back a million years ago we used to fill the tanks to the top each night to prevent condensation. For many practical reasons that's not always possible. Drain frequently and have the plane level at the time.  Nev

Whatever happened to the obligatory fuel sample as part of the pre-flight?

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I do it before first flight of the day & after refuelling. After days of high humidity & cold nights there can be a couple of mm of water in the tester. Never had anything after a refuel. That test won't find any water in the rocker cover or elsewhere in the engine.

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It's still there but the point is you can do an extra one, anytime. Just after it's agitated by the fuelling process or if not on level ground may not be the best time. Not as effective. so do a proper one.( Or two).  If you can drain the carby bowl easily do that also an d if you find water  keep going till you don't It's likely to collect at any low spot in the system and might require a high rate of flow to dislodge it.  Nev

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2 hours ago, danny_galaga said:

The water in that rocker cover would be from the atmosphere 

Why do we never find water when we pull wing inspection panels on metal aircraft in similar winter weather?

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23 minutes ago, Thruster88 said:

Why do we never find water when we pull wing inspection panels on metal aircraft in similar winter weather?

I don't know but from my experience with refrigerated vans hot travels to cold, and if the skin is impervious water droplets build up on the outside skin. Air isn't going through the skin, so I'm not sure how this water is being extracted.

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 The surface is below the dew point of the air in contact with it. Jetliners after landing may still show frost on areas where the fuel is still cold .They may have been cruising in temps of minus 58 degrees C. Nev

Edited by facthunter
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