OK to leave electric engine pre-heater on for extended periods?

[Hank Jarrett]

Re: OK to leave electric engine pre-heater on for extended periods?

Watch the wife for a new hair dryer. Hair dryers are pretty high power devices and pull a lot of current. They also usually have a GFI cord on them and when they fail it is almost always the heater elements. I just cut the cord with the GFI box off the dryer and put a female 3 prong plug on the end of the wire. PRESTO! A 3 prong, GFI extension cord! Really nice to plug almost anything in to at the hangar where you would like a GFI connection and don't have one. It's not bad in my current hangar, but my old one ALWAYS seemed to have water on the floor after any rain.
Hank

[Joel Severinghaus]

Re: OK to leave electric engine pre-heater on for extended periods?

Went out to the hangar today to check on the plane, which has been plugged in for a week now. I'd forgotten that my hangar does already have a GFI outlet, so that's covered. Don't have to steal my wife's hair dryer cord, although that's a brilliant idea, Hank.

Maybe I'm naive, but I'm not too concerned about fire risk with the extension cord. Last winter, I ran an extension cord to a battery trickle charger running continuously on a car stored in my hangar, and thought nothing of it.

I'm inclined to believe Reiff, that leaving the engine heater running continuously actually lowers the relative humidity in the engine and engine compartment. With the blanket on, even my cowlings are at the same warm temperature as the engine...

[Hank Jarrett]

Re: OK to leave electric engine pre-heater on for extended periods?

Couple of things:
1) A hair dryer pulls LOTS of current (and I took the cord from a BROKEN one, not her good one. I still have all my "special" parts, and wouldn't if I cut up her good dryer!)
2) A battery trickle charger pulls VERY LITTLE current, and like I said, I leave one untended during the day too. Not for weeks, but during the day while I'm at work and it doesn't worry me any more than a plug in clock.
3) The moisture problem (and fire hazard) with engine heaters is caused by burning FUEL. It's a completely different hazard than an electric heater where the hazard is the heater failing and causing a fire.

I'm just getting the feeling we are getting some confusion on the problems.

Electric heaters are a FIRE hazard, but one that can be controlled.
Fuel fired heaters are very efficient but are a BIG fire hazard (even for short periods) and moisture hazard over any more time than it takes to warm the engine for flight.

If I had a fueled heater I would only use it if I was next to the plane with a fire extinguisher right next to me. I just don't trust the things (even though they work great). You have to REALLY want to go flying to stand next to your plane in freezing weather while the engine warms up.
Hank

[shawn coleman]

Re: OK to leave electric engine pre-heater on for extended periods?

I have the rieff system a my plane as well and think it is great personally I don't think there is a fire hazard due to no open flame and the location of the heater on the cylinders nothing available there to cause a fire.
although I do not leave my plane plugged in continuously i think if you do it for extended periods of time , like stated in a previous post. You are going to burn off more moisture than you could generate. just my opinion

[Hank Jarrett]

Re: OK to leave electric engine pre-heater on for extended periods?

Electric heaters don't make moisture, FUELED heaters do. The electric heater should dry your engine compartment out really well, because there is only so much moisture in the air and as you increase the temperature, the relative humidity drops. A fueled heater actually raises the relative humidity by combining the hydrogen in the fuel with oxygen in the air and MAKING water vapor, which immediately condenses on the cold metal parts (remember the metal only has to be a degree cooler than the air to get the condensation). If you are going flying right after pre-heating with a fueled heater, the engine heat will drive off all the condensate, so there is no real problem, but I would NEVER use a fueled heater unless I was right with the plane because of the fire hazard.
There is still a fire hazard with an electric heater, it is just a lot smaller risk and can be mitigated with some pretty simple circuits to shut it off if the system fails. Me, I'm over conservative. I would want an extinguishing system too, but I AM a safety engineer and a little overprotective of my baby. Until I am satisfied with the dehumidifier and heater safety I won't use them. I would rather fight a little corrosion than sweep up a pile of ashes. My plane hasn't had a dryer or heater for 68 years, it can wait a few more months till I'm satisfied. When that happens I WILL have at least the dehumidifier. When it's too cold to start the engine without a heater, It is usually too cold for me to have much fun. Heater is second (maybe with a remote starter system so I can start it when I leave home for the airport).
Hank

[NY86]

Re: OK to leave electric engine pre-heater on for extended periods?

Try this experiment:

First, make sure the oil level in the sump is lower than the top of the filler tube where it enters the sump, so that the air space in the tube is contiguous with the air in the crankcase. Then, run the preheater for however long you see fit. Then, pull the dipstick out and check the underside of the cap for moisture. None == good.

[Craig]

Re: OK to leave electric engine pre-heater on for extended periods?

Hi all

Well guess I might as well jump into the fray. I currently have a Tanis engine heating system on my 172. I have been taught and I always been told to never leave it on as a full time heater. Engine heaters should be used as a means to heat the engine a few hours (8 - 10) before starting below 20 F.

The reason is that the heat causes moisture to condense in the engine resulting in corrosion problems.

See link to an article I found on the Tanis website.

http://www.tanisaircraft.com/article_info.php?articles_id=4

Like everything there are always many schools of thought.

Craig

[Jim Doody]

Re: OK to leave electric engine pre-heater on for extended periods?

Can't say if it's a good thing or a bad thing to leave a heater on for extended lengths of time. However, if I was determined to do it this is what I would use. http://www.mcmaster.com/#strip-heaters/=4elc4j Just place it under the cowl. These are available in about any wattage and are safe for extended times. They will last for years with no burnout worries. If an insulated engine cover is used with few air leaks I would guess 200 or 300 watts continuous would keep an engine DRY and ready to go. A light bulb(s) would work to determine required wattage. One of these timers http://www.mcmaster.com/#seven-day-timers/=4elkui will keep it off until next friday night for you and ready to go sat morning. 300w @ 120v eq 2.5 amps, a #14 lead cord is overkill. 300w at my house costs about 4 cents an hour. And as advised use a ground fault device. Jim

[n6346m]

Re: OK to leave electric engine pre-heater on for extended periods?

OK guys I can't stand it any more. It's time for me to show my ignorance. If I am wrong, someone PLEASE correct me.

I remember from several metorological courses that I have taken during my flying career that relative humidity is the capacity of an air mass to hold moisture. At 100% RH an air mass is totally saturated and can hold no more.
A warm air mass can also hold a lot more moisture than a cold one. That's why we don't have monsoons and tropical rainstorms here in Alaska. From that, I deduct that an air mass of 120F and 15% RH has a lot more water vapor in it than one at 32F and 15% RH. If that is the case, then the goal should be to reduce the total amount of water vapor in the engine, not necessarily the relative humidity. In Fairbanks where it is way below zero all winter, things just don't rust or corrode, there is simply not enough humidity in the air. Just look at something that's been in your freezer for sometime and see how dried out it gets. Some call Fairbanks the Davis-Monthan of the north just because it is so dry for a good part of the year.
I don't know how the Aviation Consumer tests were conducted, but it seems that it would make a difference if they were made in a climate controlled hangar where the surrounding temperatue and humidity are constant or just in a heated hangar where the outside humidity can vary considerably or if it was done outdoors with no controls at all.


I had an acquaintance in the Seattle area (where the humidity is always high)who left his newly factory overhauled engine in his Bonanza plugged in all the time and wound up having to rebuild it in a year because the insides rusted out. I have no idea what kind of pre-heating system he had installed but Continental told him that it was not covered under warranty. I have also heard of one individual who had a thermostat failure in his oil pan heater and the overheating of the oil turned it into molasses. It's a good thing that he checked the oil on his preflight.

The bottom line is that I'm pretty conservative when it comes to expensive things like airplane engines. I tend to follow the manufacturer's recommendations when I can. If they say don't plug it in, then I don't. Unless someone is able to give me a written guarantee that they will give me a replacement engine if their system fails or that somehow their testing was not done under real-world conditions. If your wife thinks that $369 is expensive for a remote system tell her how much a teardown for a replacement cam and lifters costs. I think that it's pretty cheap insurance.

I fly skis all winter here in Alaska and I have a Reiff system installed in my O-540 powered Stinson. I think it is the best system available that's why I chose it. I carry a Honda 1000 Watt generator in the baggage compartment. It only weighs 39 lbs and I can keep my battery fully charged while I'm pre-heating.

On another note, don't forget prop covers when you pre-heat your engine. I see a lot of airplanes with engine covers and no prop covers here in Alaska.
A lot of people don't realize that the propeller with all that surface area is a tremendous heat-sink. It will transfer the cold right down the crankshaft to the core of your engine. For the L2 I just put on the wood prop for the winter and I don't need a cover for it.

Well that's it. If I'm off-base let me know. I've developed a pretty thick skin over the years for being wrong a lot of time so you won't hurt my feelings, just ask my wife.

[Hank Jarrett]

Re: OK to leave electric engine pre-heater on for extended periods?

I'm with you Bob. I have NO intention of putting a heater on my engine until I have carefully tested the system where I can watch it for a long period. I ABSOLUTELY won't be using a fueled heater with a flame of any type. Just too dangerous unless you are right there with a fire extinguisher.
If I build an electric heater it has to have several safety devices and be tested to be sure it is totally safe unattended. I'm a little more hopeful about the dehumidifier. The aquarium pumps they use to push dry air around are well tested for VERY long periods and when they fail they don't catch fire or melt down, they just stop pumping. Even so I would use a GFI to power it.
One thing to remember when you talk about the humidity in air with relation to temperature is we are talking about raising the temperature of air that has a set quantity of moisture (not relative humidity, the actual amount of water in it). Just because you raise the temperature doesn't mean the humidity rises, it drops. It "can" hold more moisture, but there isn't more available for it to draw from. Your friend in Seattle got caught in a different problem. He was living in an area where the air was saturated with moisture most of the time. The warmer air in his engine had no problem sucking up more moisture from the air outside since there was so much of it. You are in the opposite end in an Alaska winter. All of the moisture is frozen and the outside air will suck up all of it from your plane. Spring in Alaska is a problem for you when the nights are cold, but not freezing, so the air has high moisture that wants to condense on the cold metal of the engine as the air outside warms up.
Best plan would be to just go flying every morning! Heats the engine up and drives the moisture off, plus it is a LOT of fun!
Hank

[NY86]

Re: OK to leave electric engine pre-heater on for extended periods?

Heating the engine oil drives the moisture entrained in the oil out and into the air, which is warmer and can hold more moisture. Then, if the top of the engine [unheated] is a few degrees cooler than the sump, the [moist] air rises up and the moisture condenses on the [relatively] cold case, from whence it drips on your Lycoming cam shaft...

[Joel Severinghaus]

Re: OK to leave electric engine pre-heater on for extended periods?

Thanks again everyone for all the additional well-reasoned debate. I've learned more useful stuff about my airplane from this forum than from any other source.

To throw some more fuel on the preheating fire, here's this from another Peter Tanis article on the Tanis website (http://www.tanisaircraft.com/article...?articles_id=5 ; scroll two-thirds of the way down to the sub-head "The Corrosion Issue"):

"...Some people have accused preheaters of being the cause of corrosion in engines. They claim that leaving them on "produces" moisture, which corrodes the engine. This is overly simplistic and inaccurate. If the engine has been operated property with the oil temp high enough, the engine can be preheated for any length of time and no moisture will be released from the oil because the oil has none to release. Even if the preheater over temped the oil and began the oxidation process there would be no moisture released. I know of one engine that had a preheater left on inadvertently for two years. There was no detrimental effect.

"By contrast if the engine has been operated in a way, which has allowed moisture to accumulate in the oil, and then a preheater has been used that overtemps the oil, acid will be formed and moisture will be released. If moisture is in the oil it takes an oil temperature of 100ºF (38ºC) before any significant amount is released. If there is the exposed metal surface then corrosion can begin because there is always oxygen present. Oils with high operational times are more susceptible to this than are new fresh oils. There are also other by products of combustion that can be corrosive and if these are mixed with the acid formed in the oil the mixture can become even more corrosive...

"There is a method of dealing with this corrosion, which works in conjunction with a preheating system. Using this method, a blower is attached to the engine crankcase breather; this blower introduces fresh air into the engine while the oil filler cap is left off and the preheater operated. As the air enters the engine it is warmed causing it to absorb moisture. The moisture is then dumped overboard as the air leaves the engine. This device, called an engine aerator, allows continuous operation of a preheater with no danger of moisture even if the engine has been improperly operated."

What do you think of this idea of blowing air through the crankcase? Would that alleviate your condensation concerns for a continuously-running electric preheater?

[NY86]

Re: OK to leave electric engine pre-heater on for extended periods?

OK, so the plan is to use an electric heating system to warm the engine and oil, then an electric blower to force cold air through the engine?

I think you'll have to purchase carbon offsets if you plan to implement that scheme!

[shawn coleman]

Re: OK to leave electric engine pre-heater on for extended periods?

I have a rieff heating system as well the Turbo model and think it is the best heating system available

I personally do not leave my system plugged in continually, because I usually just fly on the weekends and I have it on timer after four or five hours of heating at 22° i typically see temperatures approaching 200 over the entire engine .
if you were to leave it plugged in 24/7 I wouldn't see a problem at all the whole engine stays to warm to draw moisture, it might be a totally different issue on other types of heaters for example pan heaters might not have . The ability to keep the entire engine warm enough to stop the drawing of moisture in the top end. but in the case of the rieff system no worries .
Look at the dipstick after a day that is one of the first places you will see moisture . i have actually saw moisture on mine and after a significant pre-heat it goes away

[Joel Severinghaus]

Re: OK to leave electric engine pre-heater on for extended periods?

That makes me feel a little better, Shawn.

I went out to the hangar today, after the pre-heater had been running continuously for 12 days. The entire engine, and even the cowlings, were uniformly warm (and dry) under the covers. No moisture on the dipstick, but then I leave the dipstick open when the heater's on.