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#21
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Water in our oil, or just alot of hot air?
Water evaporates very well
even at sub-freezing temperatures Sublimates that is..... Rusty |
#22
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Water in our oil, or just alot of hot air?
Dave Stadt wrote:
wrote in message ... Dave Stadt wrote: "mikem" wrote in message oups.com... Dave Stadt wrote: 12 years, 235K miles and still the original exhaust system. But I bet you drive it at least 3 mi each time you start it. That's true most of the time but it still doubles your estimate for muffler life. How about the moisture in auto engines without crankcases vented to the outside world? How does it get out? Once it floats upward and bursts free, as you say, where does it go? Don't hear about auto engines with corrosion problems even collector cars that are only driven a couple of times a year. All crankcases are vented somewhere. Usually to the intake manifold through the PCV valve in modern cars. Which is a closed loop. So how does the moisture escape? Are you serious? The intake manifold goes to the combustion chambers which goes to the exhaust manifold which goes to the exhaust pipe. -- Jim Pennino Remove .spam.sux to reply. |
#23
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Water in our oil, or just alot of hot air?
wrote in message oups.com... Drew Dalgleish wrote: Running an engine on the ground is bad. It's boring and wastes gas just go do some circuits to get the oil warm. What proof is there that it is bad? And sometimes weather and circumstances don't allow people to fly. I believe that ground running is better than bare metal corroding. My engine would have been corroded a long time ago if the oil from a ground run would do that, and it hasn't been. Blue skies, Rusty One of the things we (at an auto company) have to do is make sure that cars cold start well. And, nowadays, we even have to meet emission regulations at lower temperatures. Now, the problem is that it's hard to get a lot of cold starts into a short period of time. So, what to do? One technique is to use cold fluids (water, oil, even air) to force cool an engine and get multiple cold starts per day. When some dynomometers were set up to do cold start after cold start, we started to grenade the engines in short order - largely due to oil dilution from gasoline - you get some in the crank case with every start and if you don't warm up, it builds up. Moisture from blowby builds up too. Repeated short starts are, in general, not a good thing. What you propose isn't nearly as severe, but short, repeated runs are not likely to get you to the maximum TBO. There's nothing magic about 180 degrees - but the warmer it is, the higher the vapor pressure from the water, and the more it dries out. Aircraft engines are at a bit of a disadvantage since they still just use a breather tube so the only "air" going into the crankcase is from the blowby which is loaded with water and CO2 (all engines have blowby - it's just a question of how much). The positive flow from the PCV system on cars has been shown to increase the longevity of the engines, but just sticking one on an aircraft engine won't have the same benifit since aircraft run at high manifold pressures (little or no vacuum) for extended times so you wouldn't get much flow from a PCV so all you can do is warm it up enough and run it long enough for things to dry out. Oil needs to be changed because the long chain hydrocarbons break down and viscosity changes. Also, there are a lot of additives for friction and wear reduction, foam supression, etc. that tend to break down. Carbon particles are not a problem for gasoline engines since there is almost no soot generated. Diesel's on the other hand, make lots of soot, and some of it makes it's way into the oil. If you really want to circulate some oil, crank without starting . If you want to run it, run it long enough to warm up. Short runs aren't an instant disaster, but they really aren't what you want to do for a long TBO. But, it's your engine... -- Geoff The Sea Hawk at Wow Way d0t Com remove spaces and make the obvious substitutions to reply by mail When immigration is outlawed, only outlaws will immigrate. |
#24
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Water in our oil, or just alot of hot air?
One reason for not running a car or airplane for short periods is that you
have initial startup wear. Most of the wear in cars, and perhaps airplanes too, happens at startup, when there is zero oil pressure, minimal oil on the surfaces, and the presence off some condensed moisture. If you could only run an engine on the ground for 5 minutes at a time, you would definitely not want to run it once a day. On the other hand running it like this 4 times a year would probably increase the life by making sure there is some oil on the interior surfaces. I don't know of any data that will tell us where the sweat spot is that causes the least wear. One point of evidence we do have is that engines that are not run for extended times do corrode in tell tale ways. You never want to buy a plane that has sat for extended periods. wrote in message oups.com... I just watched a program about the huge Oresund bridge between Denmark and Sweden, and there was a segment about how the corrosion problem for the bridge was dealt with. Instead of painting, they use sealed compartments that have the air humidity kept below 60%. This they said eliminates corrosion. This started me thinking about the corrosion we aircraft owners are told to guard against, since I have personally been told by an overhaul shop, that half of all the engines he sees that need work, need it because of corrosion. There are several "facts" that I am beginning to question as to their validity. The ones that come to mind a 1) You have to get the oil up to 180 deg F or the water in the oil won't evaporate. 2) Starting and ground running the engine for a minute or so is the "worst" thing you can possibly do. 3) Flying for an hour will "clean" the oil (or at least evaporate the water, preventing acid formation) so that it doesn't turn to acid and dissolve the engine while sitting idle. There are probably some others, but these three stand out the most to me. Now I am sure that what I am about to say will not go over well with some people, but I have the asbestos suit ready and waiting. My take is that these three "facts" are a bunch of poppycock. Why or how they got started is anyone's guess, but the reasoning behind some of them is understandable, for others I wonder what they were smoking at the time. My thoughts are along these lines, and I admit I could be wrong, but I don't think so. Concerning fact #1...Why does someone think that the water has to be brought to a boil before it will evaporate. Water evaporates very well even at sub-freezing temperatures,much less at the warm to hot temps created in a running engine. And at say 140 F, I can't help but believe that any water or moisture in the engine will be purged quickly. With water at that temp you can literally see clouds of vapor escaping, and this is well below boiling. Not that the hotter the engine gets the water doesn't evaporate more quickly, it does I'm sure. It's just that in the engine cases which are open to the air at the breather tube and elsewhere, any heat above say 85 F or so will be more that enough to dry out the oil in the crankcase. As evidence of this, I ground run my engine all the time and have for many years. I live in a VERY humid climate. The oil analysis reports I have done on a regular basis by Blackstone have never shown any trace of water or moisture. I recently tore done the engine for rebuild after more then 15 years of perfect service, and the cam lobes, lifter faces, and every part in the engine was shiny and totally free from rust or any other corrosion. Concerning fact #2.... We all constantly clean and oil many of the things we own such as tools, etc. It is the layer of oil that prevents the rust. I accept that if the oil is too acidic it could corrode or "chem mill" the metal, but it takes highly acidic liquid to do that, and the oils I use have acid buffers in them to deal with mild acidity. Running is the only way to re-oil all the parts in the engine, especially the cam and lifters. Just like oiling the machinists tools that I own keeps them rust free, oiling the engine keeps it rust free I would think. Concerning fact #3.... This is the one that really makes me wonder. If oil needs to be changed every 25-50 hours, how does flying for an hour clean it? I can't help but think that the longer the oil is used the dirtier it gets. I guess they think that it's "really" dirty just after starting, and you "clean" it as you fly. In closing, it seems to me that many of the things we are told are contradictory on this subject. I have witnessed many OWT come and go in my time, so common knowledge isn't always correct, lean of peak operation comes to mind. Some blockheads still don't think George Braly has it right. Blue Skies Rusty |
#25
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Water in our oil, or just alot of hot air?
Good Post, Captain!
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