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Engine heaters-good or bad?

Aviaman

Aviaman

Well Known Member
This is to start a discussion about engine heaters. I?ll begin with my thoughts and questions. When an engine case is cooled below the internal dew point, there will be condensation inside the case. This is a starting point for corrosion. It therefore would seem that heating the case would prevent that condensation, provided the case reaches a temperature above the internal dew point. And thus prevent corrosion. This seems true on the face of it, but there are two complications. One is that the oil is also being heated, thereby causing evaporation of moisture contained in the oil. This raises the internal dew point. Does this more than offset the rise in case temperature, and allow condensation ? I don?t know. Anyone here know ? The second complication is that chemical reactions proceed faster at higher temperatures. Does this increase the rate of corrosion, even despite possibly less condensation? Is there ?dry? corrosion, where humidity itself, even without overt condensation, that causes corrosion? Does the higher case temperature accelerate this (assuming it exists)? Any knowledge or ideas?
 
there is definitely corrosion with only water vapor. i thought i read on this site it is in the 60's relative humidity. i brought up the exact question to a well known engine heater mfgr. at osh. he felt the raised temp. preventing condensation offset the increased rate of reaction. he offered no proof and what is an engine heater mfgr. supposed to say? so i have been asking this question for years [ because when most recommend a higher temp. they are not even aware of increased rate of reaction] and never heard a definitive answer. i would love to hear the truth. like primer wars?
 
Heating just your sump long term will most definitely accelerate corrosion in other parts of the engine. This warning is shared by sump heater manufacturers and engine manufacturers alike. I know of a case here where an owner heated their engine bay with 300W of heat continuously year round (at $709 per year in energy usage). Twice he had significant corrosion discovered inside the propeller hub which was always attributed to excessive washing and somehow water was magically getting into the hub. It turns that the root cause was just combustion moisture already inside the engine. If one part of the engine is kept warm, then moisture will not settle out there, but in parts of the engine the temperature is less and the air can no longer hold the moisture, it will condense on those surfaces. In this case the engine had a blanket over it so the temperature was quite uniform, however the aluminum propellers are massive heat sinks ensuring the hub is at ambient temperature, so this is where the condensation occurred and subsequent corrosion. I verified everything with with a IR camera, and sure enough the hub was pretty much at ambient temperature. This owner is now using a dehydrator instead.

About 10 minutes after I shut my engine down I install my dehydrator (it gives me time to not burn myself of the exhaust when installing the crankcase vent plug). The crank case humidity is about 80% at this point. The dehydrator over the next few hours will bring it down to 10% (I stated in a previous post that the humidity reduces at about 2% per hour but it is actually closer to 5% - higher flow pumps will be even faster of course).
Once you have the humidity down, you can heat the sump all you like, because with such low humidity there will be no condensation, and if any moisture is released from the sump by heating, it will just get captured by the the air recirculating through the desiccant. I have a two 100W Reiff sump heaters attached to my engine, in fact it is plugged in right now on a timer and will kick on about 2.5hrs before I depart tomorrow morning. Even on a freezing (0?C ) morning I will get to the aircraft and my oil temperature will be at 100degF and the engine will be slightly warm to touch (I keep plugs in the engine air inlets to stop circulation). I'll fire up, taxi out and take off without having to chug away waiting for the engine to get to temperature.
Details on my dehydrator may be in the link below.
http://www.vansairforce.com/community/showthread.php?t=157922
So to answer the OP's question, engine preheaters are great if used only when necessary before start and in conjunction with dehydrators, at least based on my analysis and experience.
I hope this is of help.
Tom.
RV-7
 
tgmillso said:
Heating just your sump long term will most definitely accelerate corrosion in other parts of the engine. This warning is shared by sump heater manufacturers and engine manufacturers alike. I know of a case here where an owner heated their engine bay with 300W of heat continuously year round (at $709 per year in energy usage). Twice he had significant corrosion discovered inside the propeller hub which was always attributed to excessive washing and somehow water was magically getting into the hub. It turns that the root cause was just combustion moisture already inside the engine. If one part of the engine is kept warm, then moisture will not settle out there, but in parts of the engine the temperature is less and the air can no longer hold the moisture, it will condense on those surfaces. In this case the engine had a blanket over it so the temperature was quite uniform, however the aluminum propellers are massive heat sinks ensuring the hub is at ambient temperature, so this is where the condensation occurred and subsequent corrosion. I verified everything with with a IR camera, and sure enough the hub was pretty much at ambient temperature. This owner is now using a dehydrator instead.

About 10 minutes after I shut my engine down I install my dehydrator (it gives me time to not burn myself of the exhaust when installing the crankcase vent plug). The crank case humidity is about 80% at this point. The dehydrator over the next few hours will bring it down to 10% (I stated in a previous post that the humidity reduces at about 2% per hour but it is actually closer to 5% - higher flow pumps will be even faster of course).
Once you have the humidity down, you can heat the sump all you like, because with such low humidity there will be no condensation, and if any moisture is released from the sump by heating, it will just get captured by the the air recirculating through the desiccant. I have a two 100W Reiff sump heaters attached to my engine, in fact it is plugged in right now on a timer and will kick on about 2.5hrs before I depart tomorrow morning. Even on a freezing (0°C ) morning I will get to the aircraft and my oil temperature will be at 100degF and the engine will be slightly warm to touch (I keep plugs in the engine air inlets to stop circulation). I'll fire up, taxi out and take off without having to chug away waiting for the engine to get to temperature.
Details on my dehydrator may be in the link below.
http://www.vansairforce.com/community/showthread.php?t=157922
So to answer the OP's question, engine preheaters are great if used only when necessary before start and in conjunction with dehydrators, at least based on my analysis and experience.
I hope this is of help.
Tom.
RV-7
Click to expand...
Excellent description. I might add that . . . at operating temperatures the crankcase is filled with combustion gasses including water. It is super saturated with water and unless the temps are kept at operating temperatures there will be condensation.

This post is what I do for my engine as well, dessicate, then heat for oil warming only. Once the crankcase is dry, the dryer can be removed (24 hr), moisture will NOT return, at least not to the oil side. Circulation from exhaust and intake is another matter but not very fast.

edit: a 2017 SAE paper on EGR that said the exhaust , in theory, has a dew point between 130F and 200F depending on sulfur compounds. Mogas is extremely low in sulfur, also yielding lower H2SO4 in the crankcase.
 
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Hi Bill,

I totally agree. There will be a little condensation on surfaces for as soon as the temperature drops a little. The 80% is just what I measure on my humidity meter from the air coming out of the dipstick port into my sampling jar. I just can't get the plug into the breather tube any faster as it is near the exhaust and I'll burn myself. I figure that with 10% (or drier) humidity air constantly circulating around the engine, any surface moisture will be absorbed by the air in a short period of time. It's no different to pouring some moisture on a bench and allowing the air to evaporate. In Arizona it will disappear much faster than it will in Washington.

Tom.
 
I loosen the oil dipstick, lift it slightly and move off center after each flight where the plane is in a hangar. It is amazing how much water vapor one can see wafting out of there.
 
Should I do something different ?

1- I live in flyover country ( midwest )
2- preheat with sump heater for about 2hr before flight
3- use no lead mogas
4- open dipstick and set to the side after flight
5- I fly at least one hour weekly

Comments appreciated
 
that hour weekly is the big one. i think you have got it covered . don't forget to preflight that dipstick.
when engine is started i always try to run it up to temp. stopping an engine while cold and leaving it sit leaves moisture in it that would have been dissipated by the heat.
 
Larry DeCamp said:
1- I live in flyover country ( midwest )
2- preheat with sump heater for about 2hr before flight
3- use no lead mogas
4- open dipstick and set to the side after flight
5- I fly at least one hour weekly

Comments appreciated
Click to expand...

I do 1, 2, 4, and 5.

In a total ownership cost over life of engine, any preheat will increase engine life (or decrease engine wear) more then any issues with preheat causing corrosion, given you run the engine on a regular bases.
 
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plehrke said:
I do 1, 2, 4, and 5.

In a total ownership cost over life of engine, any preheat will increase engine life (or decrease engine wear) more then any issues with preheat causing corrosion, given you run the engine on a regular bases.
Click to expand...

I do the same thing, about twice a year when it gets below 30?F here in South Carolina.

I also use Camguard, at the recommendation of a well known engine builder.

I do NOT leave it plugged in all the time.
 
For those who live in colder climates, preheat is mandatory. We live in an area where pre-heating has been needed for the last six months +. It's been a rough winter.

One thing to keep in mind is that most "stick on" styles of sump heaters take a fair amount of time to warm an engine. In our case, with the Reiff Turbo XP system, I think we've got a total of 650 or 675 installed watts. That's not a lot of juice when compared to the heat energy required to warm 300lbs of engine. This is where remote control of the heaters is hugely beneficial.

When I want to go flying, a couple of taps on my smart phone are relayed through the cellular hotspot in my hangar ($7/month) to a smart plug and, viola, the pre-heat is turned on. Couldn't be easier. If flying in the morning, I turn the heat on when I go to bed the night before. Oil temperature is often 100 degrees or more, making engine starts a breeze.

As important as the heaters are, an insulated cowl cover is the vital second half of the pre-heat equation. Aero-Covers makes a beautiful cowl cover using Thinsulate (tm) - it really fits like a tailored suit and isn't bulky like the typical quilted covers. The slight extra cost is well worth it for the reduction in bulk and resulting ease of installation of the cover.
 
I use an EZ-Heat sump heater on my IO-360 ($150 from Spruce) and usually turn it on 6-8 hrs. before going flying with a remote switch. This usually heats my oil to 85?F, additionally I see identical temps on all 4 EGT's & CHT's which is a nice check of their operation. A good heater will be thermostatically controlled to maintain a constant temperature.
 
Preheat time

Rocket Bob says to preheat no more than 2 to 3 hours. So that is why I do 2hr and oil temp is 50F for startup with OAT in 20's.

Any debate on 2 hrs vs 8 hours? I like the idea of hitting the iphone switch in the hanger the night before :D
 
In-sump Heater?

Has anyone tried using a screw-in oil type sump heater instead of the stick-on type? My sump has an extra drain hole that accepts a screw-in heater I found. I plan to use a quick-drain plug in the other. I am thinking heating the oil directly might work better than heating through the pan...
 
it gets about as cold in n. wi. as anywhere. 150 watt sticky on the pan and 150 watts on the top of crankcase would get my jab 3300 up 70 deg. in at most 4 hrs. easy with a remote cell set up. i see no reason to heat longer than you need. i had only 300 watts so it took 4 hrs.
 
Larry,

I think you'll be fine given that you fly your aircraft so regularly. I can be a month or more between flights, hence the reason I continue to use the dehydrator. I can understand that Bob would say not to leave it on for too long, because if the engine is warmed unevenly and the humidity is high because the engine has not been dehumidified, then there is the chance for corrosion to occur. For every 10degC increase in temperature, a chemical reaction rate is doubles (Arrhenius Equation) so the aim should be get the engine to the required level, then go fly, don't sit there for ages at the high temperature, not to mention the fact that it's a waste of energy as your heater may only be able to take the temperature so far. I think I'd be heating it above 50degF though. The closer you are to operating temperature of the engine as a whole, the less the friction as everything will be expanded to its proper operating dimensions. Snuff the inlets, throw a blanket or duvet/doona over the top of the cowl and get your entire up a little further. In 2.5 to 3hrs (using a timer I set the night before ) I can have my oil up to 95-100degF.

Doug,
Screw in heaters are generally not recommended because they burn the oil. There watts per unit area is so high that they can scorch the oil and cause premature degradation. You are better off with some kind of pad heater on the sump, or a resistive heater that you insert into the cowl if there is no room on the sump.

Cheers,

Tom.
 
Doug Rohrer said:
Has anyone tried using a screw-in oil type sump heater instead of the stick-on type? My sump has an extra drain hole that accepts a screw-in heater I found. I plan to use a quick-drain plug in the other. I am thinking heating the oil directly might work better than heating through the pan...
Click to expand...

I did and really liked it, right up until it failed and almost burned up the plane.

I now have a stick on pad type heater.
 
Thanks for the commentaries. This last winter I had an electric heater under the cowl, where the warm air would rise into the engine compartment and exit through the air intakes. I left in on mostly 24 hrs a day. It was only after thinking about it that I became worried about the issues and began this thread.

Because of the commentary, I am building a dehydrator. I want it to work closed loop so that the silica will only be removing moisture from the engine, not the whole atmosphere. I assume the way to do this is to have one end at the dipstick, the other at the breather. Is there any advantage as to which is input or output? I?m planning to filter the air so no grains of silica are carried into the engine.
 
Hi John,

Mine pushes air in the crankcase vent and pulls it out the dipstick port. It doesn't really matter which. I push in the crankcase vent with the thought that it stops pulling oil into small diameter silicone air tube. I may still modify my setup a little, and put an aluminum sharp right angle bend on the crankcase vent outlet right near the exhaust to make it easier pushing the plug into and mean that I don't have oil draining down the tube. That said, it hasn't been an issue in the year that I've had the engine operational. It's just a bit awkward pushing the plug into the crankcase vent with the pipe pointing straight down just above the exhaust. The other aspect that may come into play is the natural rising of hot air. The air pump doesn't have a whole lot of power, so I thought I should work it in the direction of the natural airflow.

Tom.
 
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if it is closed loop and you keep some air moving i think input/output is your choice, whatever is easier to set up and maintain.
 
I've been plugging mine in after flights recently, there is a significant amount of moisture that condenses in the output tube returning to the silica jug.

I have mine set up the opposite way, input into the oil filler and output from the breather. No real reason why I did it that way (mainly that's how the tubing lengths worked out).
 
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