Sunday I noticed one of the fellows putting a 35 mm canister up the exhaust pipe of his Citabria then inserted a foam plug behind it. We had just come back from a breakfast run and were putting our planes away. When I asked him about it he said the canister had desiccant in it and holes were punched in the lid.

Well I know that as an engine cools it draws outside air, with water vapor, into the engine but I had never heard about this procedure. He felt that it was a big reason that his compression numbers had never changed from when he bought the plane new 25 years ago.

Anybody had any experience with this approach?

Sounds good in theory, but my experience with desiccant doesn't make me believe he's accomplishing anything other than drying out the bottom few inches of his exhaust stack, if that. The stuff simply doesn't pull that much moisture out of the air...a film cannister full won't do squat to dry out an engine. Unless it's a very moist environment, I'd hazard to guess he's causing more condensation than he's preventing by plugging the stack.

Every single time I've seen this thread in the list today, I think we're talking about a trip to the proctologist's office.

A friend of mine cobbled up some sort f air-dryer that he hooks to the breather of his O-200. Sez that Sporty's or somebody sells something similar which is where he got the idea. It had a little air pump like for an aquarium I guess, the push dry air thru the engine? Seems like you'd have to leave the oil cap off or something, to get some air flow for it to work. I know other people who pull the oil cap when putting the airplane away after flying, so that condensation will escape.
Hmmmm....

I used to be the engineer in charge of some "dry rooms" where freeze dried food is packaged. The drying systems use silica gel. This discussion got me curious, so I did a few calculations and this is the result:

A film canister of well dried silica gel will be able to reduce about one cubic foot of saturated air at 75 degrees to a level lower than 10% r.h.

That might be enough to do a small airplane engine, but unless the intake, breathers, and any other openings were well sealed, moisture will migrate into the system and rapidly saturate the desicant.

So, does this guy seal everything else up?

tom

How much time is he letting pass between shutting down the engine and sticking his stuff into the exhaust?

How much engine heat is lost, and condensation taking place during taxing?

If he doesn't run a Chinese fire drill to get the desicant in, he would accomplish the same by going to the proctologist.

He felt that it was a big reason that his compression numbers had never changed from when he bought the plane new 25 years ago.

There are so many variables that affect commpression numbers, I doubt the dessicant is at the top of the list.

Bill

The best thing to do is fly it often, at least once a week for an hour or so. If you are going to put it away for an extended period, there are preservation methods, but they are not practical for short periods.
For whatever it's worth, the engine crankcase is an open system even with the oil cap on, because the breather is open.
If he is willing to do the film cannister thing, then he is the type that is probably doing other things as well to care for his engine and these other things may be more important than a film cannister of silica gel.

When leaving my airplane for extended periods I put some tennis balls over the exhaust (cut "X" in ball to slide over pipe). It should slow any convective air flow of moist air. It might not accomplish anything, but at least I feel like I am doing something...short of flying every week like A64 stated.

I used this technique once when I stored the 180 for three months one winter, but I used four large bags about the size of a sandwich baggie, pulled all the plugs and put dessicant plugs in, plugged the breather, and taped the air filter. The engine came thru OK, no rust, but all the dessicant was waterlogged.

If you use this idea it will require about ten times the volume of a film cannister of silica gel, and you should plug the breather and put some Saran wrap over the air filter.....then plan on drying the silica in your oven about twice a month.

The technique I use now, and have been for the last 12 years, is to put a 75 watt halogen (3000 hr) bulb as far up the exhaust pipe as I can get it, plug that with a closed cell foam plug ( I use a piece of pipe insulation), plug the breather, plug the cowl openings and cover the whole cowl with an old sleeping bag. This keeps the engine at about 35-40 degrees with very little daily change (OAT of ~15-20), so it doesn't breathe much. It's in an unheated hangar in Jerome, Idaho, which does get a semi-permanent inversion from December to March, so it's quite moist.

I sometimes only fly the plane once every three weeks in the winter, but I have never had any rust. One good way to check for moisture in the winter is to pull off the oil filler cap and look for visible condensation. Beads of moisture or grayish sludge is an indication that there is too much moisture inside the engine, and/or that it's not being flown long enough to boil off the water.

Keep in mind my engine is a Continental , so the cam is not so exposed. If I had a Lyc, I would NEVER let it go more than 10 days between flights.

I also have been using Lenckite AVBlend since I bought the plane in 1994, and exclusively AeroShell 40 or 50 weight. All I know is that when I tore the engine down after ten years of this regimen it was perfectly clean inside, the cam was still fine, and there was almost no sludge anywhere, so I am going to keep using this stuff as long as they make it.
( Too bad it didn't do anything for a cracked case! )


Rocky

I don't think the breather is sealed. I think this guy is just very meticulous. He has a pristine VW Thing (remember that buggy?), a '54 Vette, a Great Lakes, and other interesting toys. So I think he is just good at taking care of mechanical stuff.

Does the desiccant help? Who knows but it apparently doesn't hurt. I guess it wouldn't be worthwhile saying anything to him. It was just one of those oddities that I stumbled across that kinda makes you think for a moment that maybe you missed something obvious.

I recently read some info from Lycoming, oil companies, and other engine experts on preventing engine corrosion. It's my understanding that everything on the combustion side of the piston gets a glaze that slows down the start of corrosion for a few weeks. The area where moisture is a more immediate problem is on the cam because oil film is not held in place on the lobes. Desiccant would need to dry the air that is drawn into the engine as it cools and the moisture that is in the combustion gasses that have blown by the rings. I doubt it is worth the trouble unless the all other openings were sealed, like Tom suggested.

On a somewhat related topic... I took my primary training from an old timer. He taught me pull the prop though for four blades to check for compression as part of my pre-flight. It made since to me and was a habit that I've held on to. Recently I read a bulletin from Lycoming (I think) that discouraged the practice. It said that doing that wipes the oil from the camshaft lobes and causes metal-to-metal contact during the first few seconds after engine start. I haven’t decided if I’m going to change my practices yet, but it is good food for thought.

On a somewhat related topic... I took my primary training from an old timer. He taught me pull the prop though for four blades to check for compression as part of my pre-flight. It made since to me and was a habit that I've held on to. Recently I read a bulletin from Lycoming (I think) that discouraged the practice. It said that doing that wipes the oil from the camshaft lobes and causes metal-to-metal contact during the first few seconds after engine start. I haven’t decided if I’m going to change my practices yet, but it is good food for thought.

My mechanical prowess is well known on this forum, but for the life of me I don't see how pulling the prop through by hand pumps any less oil than pulling it through with the starter.

ravi wrote:...I don't see how pulling the prop through by hand pumps any less oil than pulling it through with the starter.

Ravi,

I think you are right about pumping oil, but that only takes care of the areas that are pressure lubed. The cam lobes and several other areas are splash lubed. Below is a link to Lycoming service letter L180B just so you know that it wasn't my arse from which I pulled this info.

http://www.lycoming.com/support/publications/service-letters/pdfs/SL180B.pdf

There is also a min. RPM for the pump to prime, it takes a second or two to get oil pressure after starting, for instance.

At the last overhaul I installed a preoiler. Best thing I ever did. The airplane will sit for several weeks when I am at work. Plug in the sump heater, drink a cup of coffee and tell several "noshitthereIwas" stories in the office, hit the preoiler till I get solid pressure for about 15 seconds and start it up. No lifter clatter and instant oil pressure. The engine thinks it had just been flown. Also built a homemade dehydrator similar to the commercial ones for about 20 bucks. Works really well.

a64pilot wrote:There is also a min. RPM for the pump to prime, it takes a second or two to get oil pressure after starting, for instance.

On my little Rotax, it takes 10-20 "blades" to get oil pressure when cranking by hand. On a starter start, the oil pressure is there in maybe three seconds. This is with a stone cold engine at perhaps 40 degrees and sitting overnight.

tom

Kenny Chapman wrote:At the last overhaul I installed a preoiler.

I've known other folks that have put preoilers on various rigs. Most of them didn't keep the rig long enough to know if it helped or not. I think most folks that even consider such a move take way better care of their stuff than the average guy, so it is hard to tell. I've always liked the concept, but given a modern auto engine will last 200K and an aircraft engine will outlast my expected usage, I haven't felt it worth the money and weight.

tom

I asked Paul McBride about pre oilers, and his response was that you still have the camshaft sitting there, corroding between flights, and by the way, the spot where the cam and follower meet isn't pre-oiled.

There are two different issues here regarding pulling an engine through prior to flight. I think this is a left over from radial engine days. On a radial, you do this prior to each day's flying, because these engines can get hydraulic lock by oil in the case leaking down into the combustion chambers of the bottom cylinders. Trying to start the engine in this case would seriously damage the engine. Oil is not compressible....much.

Pulling your prop through won't help "pre-oil" your engine because, as noted above, the oil pump doesn't move enough oil in just a few turns and that slow to do any good.

Now, scraping the oil off the camshaft whilst turning the prop through is an issue, but perhaps a bigger issue is scraping all the oil residue off the cylinder walls. So, now, there's no lube between the rings and cylinder walls.

As to dessicants, I doubt they do any good at all unless you are actually pickling the engine. And, if you are going to store the engine for a couple of months, you really should pickle it with pickling oil.

I use ASL Camguard with every oil change. There is some impressive scientific testing of this stuff available AND it is one of the very few additives that is now FAA approved. See http://www.aslcamguard.com/, and read their test results.

I used to use MMO, but gave up on that stuff. I doubt that it or most of the other additives do anything, but ASL actually has some testing. I've asked Lycoming reps about the stuff, as well as a well known rep from Aeroshell, and they all said they think this stuff actually has some value.

MTV

MTV,
Where do you get the cam guard? The link doesn't work. FWIW, getting an additive FAA approved means you have proved it does no harm.

It's the comma being included in the link that screwed things up, delete the comma and it works