That’s a great article, denopa – thanks for posting it. I will read it in detail tonight.
[ local copy ]
flying club plane, typical usage 40-80 hours per month, flew every day (reached TBO on average once every 2 years). Cam failed on one engine halfway to TBO due to corrosion and spalling.
It really flew every day, 365 a year? I would say corrosion is completely impossible then.
Peter wrote:
It really flew every day, 365 a year? I would say corrosion is completely impossible then.
Not far off it. In a place where the weather is reasonable and it’s the cheapest C172 to rent within 100 miles, and the aircraft is in good rig and the owner keeps it well maintained including the preventative stuff so it keeps flying, the plane will fly a lot, including Christmas Eve and Christmas Day (I’ve flown that particular plane on both of those days) The O-320-H2AD is a notorious engine for eating camshafts, the AD in H2AD stands for “airworthiness directive”
@ denopa: the article is convincing, many thanks!
Camguard obviously works, in combination with dehumification even better. Engine corrosion was my biggest concern, I´m a bit calmer now.
The dehumidifier article is revealing and reminds me that if you fly an engine that doesn’t reach high oil temperature even after running for extended period, post shut-down corrosion is an issue. Small Continentals are an example, it’s often hard to get the oil hot on a little A-65. In my experience, if you pull the oil tank on one of these engines, providing a pretty good view of the crankcase internals, you may not like the corrosion you see. One thing I think may help is to pull the oil filler cap after flight, you’ll see water vapor coming out – which is also concerning but I’m guessing better that letting it condense inside the engine.
I’ve never done it, but it’s not clear to me why running an engine for a very short period, say 15-30 seconds periodically wouldn’t circulate/splash oil adequately and wipe off whatever corrosion is starting on the cam and lifters without introducing a lot of water vapor from combustion. It may be true that start-up is when a lot of engine wear occurs, but if you’re going to start it once a week anyway what difference to that issue does it make how long it runs afterward? Maybe the higher viscosity of cold oil would be an issue in distributing oil in cold weather. Just a thought, as I say I’ve never done it.
Just read the whole article.
The findings are quite sensational.
Not surprising is that the use of the engine heater reduced the RH from the ambient to very low values, even single percentages. But most pilots cannot use such a device – due to a lack of a power connection in the hangar, due to airport politics preventing any such equipment, etc.
The two big findings were
That Exxon Elite is as good as plain oil with Camguard (from the corrosion protection point of view) is an interesting finding. I used Exxon Elite for some years but didn’t like it because it created a huge amount of watery sludge under the dipstick and more importantly (because it is not visible there) under the rocker covers. Others users have confirmed this.
So there you go… with the best lubricating practices you have about 3 weeks max between flights before your engine starts to rust.
Peter wrote:
The RH inside the engine rises rapidly after shutdown, eventually (when the engine is cold) creating almost “IMC” conditions – sufficient to rust un-oiled steel in 4 days, or steel oiled with Philips oil in 5 days. This tells us that a quick engine run, just to spread the oil around, does next to nothing.
No, it actually tells us that flying (for whatever period) does nothing because the water in the crankcase comes from the combustion process and after every flight, there will be more water in the oil than before the engine was turned on.
There are a few things that help:
1) Let the damp air evaporate but that is hard to do (open oil filler neck but how much will that do)?
2) Replace the damp air with dry air using an engine dehydrator (like the one I built)
3) Keep the air inside the crankcase warm to decrease RH
It’s funny that the best way to get an executive summary of some article is for me to post something which somebody disagrees with and then we get it quite fast.
achimha wrote:
No, it actually tells us that flying (for whatever period) does nothing because the water in the crankcase comes from the combustion process and after every flight, there will be more water in the oil than before the engine was turned on.
I’m not sure I agree with your understanding of this, nor Peter’s. For rust to appear, you need two things: water in liquid form and unprotected surfaces (it’s not the water in the oil that matters, it holds very little of it to start with). Flying or warming the engine allows for the oil to spread around and protect your engine.
So to me the executive summary is:
- fly often to allow oil to be spread around
- keep moisture at a minimum with a dehydrator
- keeping the air inside the crankcase warm helps, but it’s really to prevent cold starts that the author of the article does it, not to prevent corrosion.
Flying or warming the engine allows for the oil to spread around and protect your engine.
Agreed, but according to the report this works only for 4-5 days, which is not a lot even for a very frequent flyer. I don’t find it surprising that oil runs off the steel in 4-5 days, especially when everything is at some +70C when you shut down and will take considerable time to cool down internally.
keeping the air inside the crankcase warm helps
Agreed too – raising the temperature even a little will increase the temp-DP spread to a point where no condensation can take place. This is why I suspect that study is not complete. If say the OAT is +10C and you heat the engine to +15C, then given that the crankcase is vented to the outside anyway (which will equalise the partial pressure of the water vapour between the two places) no condensation should be happening.
Similarly, if you attached a plastic bag with a bag of silica gel to the crankcase breather, that will suck out water vapour from the crankcase, and you need to suck out only a small amount of the water vapour to eliminate the condensation potential. This opens up a more viable solution (than an electric heater with all its “political” issues) for reducing the RH inside the engine. It is probably better than forcing dried air up the exhaust, which needs power and needs a lot more silica gel to dry the continuous airstream.
If there was no crankcase breather then the situation would be very different…
I made a simple, home made solar powered dehydrator which is a “Closed Loop” as far as possible. Air is drawn from the exhaust stacks and the crankcase breather, passed through a sealed box containing about 2 Kg of silica gel, then the dried air is fed back to the engine through the oil filler. Since it is not easy to block the intake to really seal up the crankcase, I keep the throttle fully closed, so as to restrict airflow as far as possible, and I also place a couple of large bags of silica gel inside the cowling for good measure.
Motive power comes from a solar powered “Pond Aerator” pump. It cycles on and off all day in anything other than very dull daylight, the specification says 120lph but even at a fraction of that, it is probably scrubbing the air inside the engine several times a day – and thus it gradually dries out the engine by constantly recirculating and drying the air
. The various parts for the engine / exhaust caps are 3D printed, and the airtight compartments are made from “Lock & Lock” air tight food containers.
I use Camguard too.
