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turning pre-heat off?

O

odens_14

Well Known Member
So this year I finally got a cell wi-fi switch so I can turn on (or off) the pre-heater from home.

I've typically been switching it on the night before I want to fly. This weekend it was my intention to fly Sunday morning, but the morning fog lasted longer than forecast so I wasn't able to fly as planned. I've always read it's bad to leave sump heaters on full time; so my question is: is it better to turn my heater off or leave it on until I'm able to fly. I'm typically limited to flying on weekends during pre-heat season with my work schedule and available daylight, so it's likely at least a week and sometimes two or even 3 if the weather works against me. the heater is a 150 watt sump pad and the cowl is covered by full wraparound insulated cowl blanket.

In the past I've always just let the heater go until I was able to fly out of convenience and not wanting to drive out when I couldn't fly but now I could easily turn it off if that's somehow better for the engine.

What are your opinions?

(in this situation I was able to sneak out for a sunset flight with my boy yesterday afternoon so it's not on but thought I'd still ask for next time)
 
More recent information suggests that it is better to leave pre heaters on all of the time with the oil cap removed if you have both a oil sump heater & cylinder heat.
Tanis recommends leaving it on all of the time.
 
Jetmart said:
More recent information suggests that it is better to leave pre heaters on all of the time with the oil cap removed if you have both a oil sump heater & cylinder heat.
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What's the source of the new info? Got a link or anything?

I'm not arguing or pushing back, but I'd like to take a look at the study/report/article.
 
https://midwestflyer.com/?p=5742

https://www.tanisaircraft.com/faq-frequently-asked-questions

The best article was Consumer Aviation which I can't get to. I did find this

http://www.reiffpreheat.com/FAQ.htm#QA3

https://www.aviationpros.com/home/a...-engine-preheaters-be-plugged-in-all-the-time

https://www.aopa.org/news-and-media...aircraft-maintenance-proper-engine-preheating

Many aircraft owners did studies using RH meters and found that the humidity went down in the case if both the the oil sump and cylinders were heated. raising the temp automatically reduces relative humidity.

It's a very hard thing to figure out conclusively. I operated a twin for many years with Lycomings and had better luck leaving the Tanis heater, both oil sump and cylinder head, on all the time with the oil cap pulled and left off immediately after shut down.

I would definitely not shut it off once it was turned on unless I flew.
Just my opinion.
 
The concern I have is condensation as the engine cools after flying or cooling down from an aborted pre-heat. I immediately put it on a dehydrator to pump dry air through the crankcase, through the dipstick tube and out the crankcase breather.
 
MacCool said:
The concern I have is condensation as the engine cools after flying or cooling down from an aborted pre-heat. I immediately put it on a dehydrator to pump dry air through the crankcase, through the dipstick tube and out the crankcase breather.
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I get the concerns about the cool down after engine running; excessive amounts of moisture present. However, you really can't avoid temp swings and condensation. Here in the midwest spring and fall, we can see 30* temp swings many days from night to day. Fronts also routinely create 40* drops or more. Temp swings simply can't be avoided, unless you have both a heated and air conditioned hanger. No sense worrying about it.

Just a week or two ago, we had a high of 70 and two nights later it was 25. Not much different than aborting your pre-heat in winter. I just can't see being worried about turning your heater off, yet not worrying about the same thing when mother nature does it.

If you're truly concerned, you are best to leave your heater on continuously. However, I have not don the research and do not know what, if any, risks from that might be. At a minimum, there is a fire risk. Would you trust your hair dryer running all day in your house while you were at work? Unregulated resistive heating elements make me nervous for long term use, excepting those specifically engineered for that purpose.

Larry
 
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Relative to parts wear, Lycoming says you should preheat their engines before starting when ambient temp is 10F, but I have been using 40 as the temp where i turn on the preheater. I don’t like the idea of leaving my engine heater on all the time....I have it on a cell switch (Switcheon) and only turn it on a few hours before I fly. As for condensation, rather than change the dew point by heating the engine 24/7, I’ve elected to do it by lowering the humidity of the air in the engine. Keeping it at 10-15% relative humidity drops the dew point in the engine to about -30F on a 10F day. cheaper and safer IMHO.



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I can’t think of a better excuse to go flying. It’s like getting paid to fly. You are saving your expensive engine. Do this at least once a week, preferably twice a week.
I’ve owned my hangar for over 20 years, and the temp inside has never gotten below 40*F with the big door closed, no matter how cold it is outside. My ceiling and bifold door is insulated, interior walls are not (nested T hangar). I still preheat before flying any time the OAT is below 45*.
 
MacCool said:
The concern I have is condensation as the engine cools after flying or cooling down from an aborted pre-heat. I immediately put it on a dehydrator to pump dry air through the crankcase, through the dipstick tube and out the crankcase breather.
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It would seem that keeping the engine temperature sufficiently above the dewpoint at all times would eliminate any chance of condensation. If you can keep the engine temp at say, 60-70F, and the dewpoint in the winter months is in the 10-40F range (in the Northeast), the chance of condensation seems pretty minimal. Am I missing anything? Seems like a case to keep it plugged in all the time.
 
brian, your assumption seems logical but steel will rust without h20 present in liquid form. and the ''rust rate'' doubles with every 10 deg. c. increase in temp.
this whole thing is so full of variables...........it seems to me the complete answer is heat when needed for preheat and dehumidification of a closed system.
 
I'd agree with the post above this one.

Previously, I always left the heat on all winter. What I absolutely didn't want to do is turn it on and then not fly. So if it was on, I left it on until I flew. My hangars in the spring especially, get very humid, to the point that the wing bottoms will drip moisture at times, depending on the temperature and thaw going on. I didn't want heat/cool cycling to build up even more moisture in the engine. When it was heated, it was always over 90F. (Over 130F with my Reiff Turbo XP) I was satisfied with the arrangement.

A year ago though, I finally bit the bullet and I'm so glad I did, and built a dehydrator for both planes. Now I run that 24x7 after a quick venting after flight. This will suck out any moisture from in the engine and keep it very dry.
At this point, I am much less concerned about temp cycling the engine, because it will be dry inside either way. So I've been able to save heating costs by only turning on the heater before I plan to fly. I still follow the rule that once it's on, it stays on, but honestly I don't think I would have to.

There is still the fact that the outside components of the engine will build up moisture with temp cycling, but in my environment I'm not quite as worried about that. It does stay very warm under the cowl though, so if I leave heat on all the time that would not be a worry either.

At any rate, if you have any concerns at all, my advice is to absolutely build a dehydrator, since it's simple to do. Then use that all the time. If you do that, you can basically do what you want with the heater and have little to worry about other than the inconvenience of not having it heated when you want it to be.
 
Northernliving said:
It would seem that keeping the engine temperature sufficiently above the dewpoint at all times would eliminate any chance of condensation. If you can keep the engine temp at say, 60-70F, and the dewpoint in the winter months is in the 10-40F range (in the Northeast), the chance of condensation seems pretty minimal. Am I missing anything? Seems like a case to keep it plugged in all the time.
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I agree, preventing corrosion is about keeping the air in the crankcase/upper engine above the dewpoint and there are two ways to do that. I have elected to do it by keeping the humidity inside the engine low with a dehydrator. The other way to do it, as you mentioned, is keeping the temperature of the air inside the engine above the dewpoint, and there are two ways to do that…a heated hanger, or an engine heater. A heated hanger is probably the best way but that is not a possibility for me, and I prefer not to leave the airplane plugged in all the time, so I opt for continuous pumping dehydrated air through the engine 24/7. I save my Reiff turbo heater for on-call warming the oil, and decreasing dissimilar metal expansion — the damage caused by cold weather starts (supposedly). It certainly is a debatable point, and is often argued in numerous threads in aviation forums all over the web.

The dehydrator I built cost about $45 (I bought an extra 7.5 lbs of silica gel so I could rotate). I also agree with the concept of “flushing” the engine. The internal combustion process generates a lot of water and after you shut the engine down in the hanger I think it’s it’s a good idea to get rid of it. I have a pool toy inflator that I run for about 20 minutes after shutdown through the dipstick tube to accomplish that.



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MacCool said:
I agree, preventing corrosion is about keeping the air in the crankcase/upper engine above the dewpoint and there are two ways to do that. I have elected to do it by keeping the humidity inside the engine low with a dehydrator. The other way to do it, as you mentioned, is keeping the temperature of the air inside the engine above the dewpoint, and there are two ways to do that…a heated hanger, or an engine heater. A heated hanger is probably the best way but that is not a possibility for me, and I prefer not to leave the airplane plugged in all the time, so I opt for continuous pumping dehydrated air through the engine 24/7. I save my Reiff turbo heater for on-call warming the oil, and decreasing dissimilar metal expansion — the damage caused by cold weather starts (supposedly). It certainly is a debatable point, and is often argued in numerous threads in aviation forums all over the web.

The dehydrator I built cost about $45 (I bought an extra 7.5 lbs of silica gel so I could rotate). I also agree with the concept of “flushing” the engine. The internal combustion process generates a lot of water and after you shut the engine down in the hanger I think it’s it’s a good idea to get rid of it. I have a pool toy inflator that I run for about 20 minutes after shutdown through the dipstick tube to accomplish that.



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Thanks Mac. I'm about to install a new engine, and I'd like to build a dehydrator. Can you point me to pics of yours design?
 
Some thoughts:

1. Steel will not rust without the presence of water or some other electrolyte. (water vapor alone isn't enough, it has to condense). Any corrosion that might occur without water will be extremely slow.

2. If you keep the pre-heat on, with the oil cap ajar, there will be a natural convection of air into the breather and out of the oil filler. Since you are heating above ambient, there is no chance of water condensing from the air flowing into the breather tube and through the engine. An automatic dehydrator.

3. This scenario will condense water on aircraft parts: Aircraft is in a non-insulated hangar, on a clear night. The hangar (and aircraft) may get colder than the ambient temperature by morning. Later that morning you open the hangar door, letting air in which has a dewpoint higher than your aircraft parts. Now condensation will occur. It will be a transient, at least.

4. Shutting down and letting the engine get cold without a dehydrator or opening the oil filler is worse case.

5. Preheating, not flying and then shutting down pre-heat should be no different than if you did nothing.

6. Fly weekly, get your oil temps into the 170's or above, and don't worry about any of this too much.
 
Destroyed the camshaft

Personal experience has taught me to never leave the heat plugged in longer than needed to warm the engine prior to takeoff.

I owned an Apache a few years back. Dual Lync O-320s. I installed heated sumps and ran them all the time in a hangar that often went below 0 in NH winters.

A couple of years went by and both engines had to be overhauled, camshafts were both rusted and destroying the lifters.

I've installed heaters on my RV sumps but will only run them to warm the engine prior to takeoffs. I suppose the added cylinder heaters may solve the problem but I don't feel like taking the risk.
 
I've always presumed that condensation inside an engine could contribute to corrosion, so if that's true it makes sense to me that preventing that condensation is something to strive for. When the air temperature drops below its dew point, excess moisture will be released in the form of condensation. If you're worried about corrosion in your upper engine (I am), it therefore seems worthwhile to have a good understanding of the relationship of temperature and dew point. This is not a problem just for winter. You can condense water inside your engine in the summer too.

I found this online calculator to be helpful in deciding whether to minimize condensation, summer OR winter, by heating the engine vs decreasing the humidity inside of it.

DEW POINT CALCULATOR

Some people don't think condensation is an issue, and it probably isn't in an aircraft that's being flown a lot, but for airplanes that aren't, or might sit for awhile for a major repair, either on the airplane or on its pilot, I believe it to be something to consider. YMMV. As cheap and simple as a dehydrator is, I can't see a good reason not to use one.
 
Northernliving said:
Thanks Mac. I'm about to install a new engine, and I'd like to build a dehydrator. Can you point me to pics of yours design?
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Simple stuff....

I bought two 7.5 lb containers of silica gel. When it turns pink enough, I empty it back into its bottle and refill the dehydrator with the other 7.5 lb....I then take the pink stuff home and pop it in the oven for awhile til it turns blue again. I have to do that about every 30 days.

The #6 stopper fits well into the dipstick tube of my IO-320. Right now I'm running the thing open...working on getting a way to return the air from the breather back to the pump (need a pump with a barbed inlet for the air intake). Currently I run about 13% humidity inside the dehydrator, which is what I'm pumping into my engine. If I use return air for the intake, I suspect it will drop even more than that and I won't have to change the silica so often.

These things are all around the web, I can't claim the design. Good luck.
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MacCool said:
Simple stuff....

I bought two 7.5 lb containers of silica gel. When it turns pink enough, I empty it back into its bottle and refill the dehydrator with the other 7.5 lb....I then take the pink stuff home and pop it in the oven for awhile til it turns blue again. I have to do that about every 30 days.

The #6 stopper fits well into the dipstick tube of my IO-320. Right now I'm running the thing open...working on getting a way to return the air from the breather back to the pump (need a pump with a barbed inlet for the air intake). Currently I run about 13% humidity inside the dehydrator, which is what I'm pumping into my engine. If I use return air for the intake, I suspect it will drop even more than that and I won't have to change the silica so often.

These things are all around the web, I can't claim the design. Good luck.
..
Click to expand...

Looks great, What does the T in the line do? Is the line to the engine coming off the upper or bottom side of the container?
 
My thoughts

I’m basically a fair weather flyer now days although I still do “practice” ILS and RNAV approaches almost every time I fly. The reason I mention this because instead of leaving my Taniff block heater plugged in or turning it on remotely before I fly (can’t do remote due to lack of internet access at airport hangar) I just arrive an hour plus early and plug in the block heater. I then visit a few airport friends and/or take care of other chores giving the heater time to do its thing.

I’ve found that given an hour the block heater will warm the oil up to above 60 degrees F which I consider sufficiently warm enough for starting. Haven’t once notice my oil temps below 60 after starting following this approach. I don’t have cylinder head heaters. Oklahoma temperatures can get quite low.
 
Jetmart said:
Looks great, What does the T in the line do? Is the line to the engine coming off the upper or bottom side of the container?
Click to expand...

The T-connector is just because that particular model pump has two air outlets. I could have just capped one of them, would have been the same volume but they included the tubing and the T-connector so I just used that.

On mine, the pump pumps air into the barbed fitting on the bottom, through the dessicant, and out the barbed fitting at the top on the opposite side. That in turn is connected to the tubing/stopper that hooks up to the dipstick tube. Pumps in dry air through the dipstick and exits through the crankcase breather.

Others prefer to hook the cannister outflow to the crankcase breather and vent out the dipstick. I don't think it matters and my way prevents me from having to lay on the ground to slip a tube over the breather tube.
 
Tankerpilot75 said:
I’m basically a fair weather flyer now days although I still do “practice” ILS and RNAV approaches almost every time I fly. The reason I mention this because instead of leaving my Taniff block heater plugged in or turning it on remotely before I fly (can’t do remote due to lack of internet access at airport hangar) I just arrive an hour plus early and plug in the block heater. I then visit a few airport friends and/or take care of other chores giving the heater time to do its thing.

I’ve found that given an hour the block heater will warm the oil up to above 60 degrees F which I consider sufficiently warm enough for starting. Haven’t once notice my oil temps below 60 after starting following this approach. I don’t have cylinder head heaters. Oklahoma temperatures can get quite low.
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I have no wifi either. That would make it simple -- I'd just have Alexa start the heater. I live about 10 miles from the airport, so to avoid the drive back and forth to plug in the plane, I instead use a cell-connected Switcheon https://switcheon.com/ . Brilliant device. Very reliable, and by far the cheapest to install ($199, plug and play). The cell signal uses IoT (Internet of Things) over LTE and is therefore is remarkably cheap. And first year is free.
 
MacCool said:
The T-connector is just because that particular model pump has two air outlets. I could have just capped one of them, would have been the same volume but they included the tubing and the T-connector so I just used that.

On mine, the pump pumps air into the barbed fitting on the bottom, through the dessicant, and out the barbed fitting at the top on the opposite side. That in turn is connected to the tubing/stopper that hooks up to the dipstick tube. Pumps in dry air through the dipstick and exits through the crankcase breather.

Others prefer to hook the cannister outflow to the crankcase breather and vent out the dipstick. I don't think it matters and my way prevents me from having to lay on the ground to slip a tube over the breather tube.
Click to expand...


Thanks. That helps with the construction.
 
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