Is it bad to leave the engine heater on for 5-10 days between flights? Would this procedure cause more condensation than leaving the engine cold then heating over night before the flight? I use a Aerotherm heater.

Thank you Rob

Rob,

Frankly, I don't think leaving a heater running in an engine compartment hurts anything except maybe your utility bill.

In Fairbanks, one of our pilots felt like he was "on call" at all times. Cessna 185 parked outside, so in winter, he ran a Tanis high temp heat system, all winter. Of course, in fact he only actually flew the thing a couple times per winter.

A couple years later, I wound up flying that airplane (with the same engine) for a year and a half or so after the crankshaft broke on my assigned airplane. I never saw any indication the engine had suffered any adverse effect being plugged in for several winters, and hardly flown. That engine went to tbo, in fact, about the time I got another airplane assigned.

I think one of the serious enemies of engines is moisture. So, heating an engine up, then not flying it, and allowing it to cool to ambient is a pretty bad idea, in my opinion. If you heat it up, fly it.

But, leaving the engine at a constant (warm) temperature for long periods of time is probably not as damaging.

The only down side I can think of is that, of course, metal corrodes faster at warmer temperatures. That said, I'm not sure the difference in temperatures makes that much difference.

Of course, the best medicine for any engine is to be flown regularly and get engine temps up to proper temps.

MTV

I've heard running the engine-mounted heaters 24/7 isn't a good idea,
it can cook the oil and/or promote moisture condensing inside the engine.
I used to hang a 125W heat bulb under the engine on my last 2 airplanes,
with a blanket over the cowl it worked great,
but in between the cowl flaps & the mufflers that just won't work with my C180.
Since it doesn't get all that cold around here, I've just been going without winter heat,
but we do get cold snaps (like a couple weeks ago) so it's nice to have something.
A friend of mine runs one of these, I just ordered one.
https://www.aircraftheaters.com/aircraftheaters
Keeps the engine compartment at a steady 70 degrees

hotrod180 wrote:I've heard running the engine-mounted heaters 24/7 isn't a good idea,
it can cook the oil and/or promote moisture condensing inside the engine.
I used to hang a 125W heat bulb under the engine on my last 2 airplanes,
with a blanket over the cowl it worked great,
but in between the cowl flaps & the mufflers that just won't work with my C180.
Since it doesn't get all that cold around here, I've just been going without winter heat,
but we do get cold snaps (like a couple weeks ago) so it's nice to have something.
A friend of mine runs one of these, I just ordered one.
https://www.aircraftheaters.com/aircraftheaters
Keeps the engine compartment at a steady 70 degrees

Neither Reiff nor Tanis systems will "cook" or burn the oil in the sump. You're putting out bad information.

Stay away from the "automotive" silicone heat pads, which are not thermostatically controlled. There are simple heat pads with thermostats, designed for aircraft use as well.

Constant warmth doesn't "create" moisture, either. If there's moisture in the engine (and there always is), then there is always a potential for corrosion, but constant heat tends to drive that moisture off, not make it worse.

There are engine heaters and there are engine heaters. Considering the cost of an airplane and engine, I'd spring for one that is properly designed for the job, made by either Reiff or Tanis.

That said, it's my policy to plug the heater in the night before I plan to fly if possible, rather than leaving it plugged in all the time. That's mostly a cost of electricity thing, though.

MTV

I dont think it's a problem with the aerotherm heaters Rob. Since you are moving so much air through the cowling you won't cook the oil, and I dont think you'll make much if any moisture either. They do seem like a great way to go.
How do you like it BTW? I'm seriously considering one as I have multiple aircraft come through my shop in the winter and the portability and ability to use it on different airplanes makes it really nice. Can you give us a PIREP please?

David

I have a Reiff Standard on my airplane, plus the optional oil cooler heater. The Standard heater consists of 50 watt bands around the base of each cylinder and a 100 watt aluminum heater glued to the sump, plus the 25 watt aluminum heater glued to the oil cooler. With a cowl cover and prop and spinner covers on it, it heats the engine to a pretty consistent 80-90F, both the oil and the CHTs, even in bitter cold. Without the covers on it, the temperature is about 20F less. This is in an unheated T-hangar. Occasional experience parking it outside and plugged in, the covers make a much greater difference, as any breeze dissipates the heat significantly.

For the first couple years, I had a thermostat on it, and then for another couple years, I had a cell-phone switch on it. Both burned out and seemed pretty superfluous, anyway. Now I just leave it plugged in all the time (no extra cost added to the hangar rent). I doubt that there's any sort of damage by doing so, and it's a lot less damaging to the engine and accessories to be warm than to attempt to start it in really cold weather.

Oh, and checking the oil, it's definitely not "cooked". The dipstick is warm to the touch, not hot.

Cary

I think my heater glued to the bottom of oil pan is a pep boys special. It for sure does not have enough watts to bring the oil to typical operating temperature so it cannot burn the oil. I only use it when below 40

Thank you one and all. I read each reply. I also went back to Aerotherm web site, they concur, no ill effects from just leaving it on.

David, we don't have extreme cold around here. The Aerotherm seems to work great. Not sure how well it would work out side in extreme weather.

Thank you all...Rob

I think if one has the option to kick on the heater when needed the day before it is probably better than leaving it on all the time, but if thats not possible or practical leaving the heat on is way better than no preheat... heat accelerates chemical reactions but i would suspect the air is so dry in most regions where you need preheat that moisture and corrosion are probably pretty small on the things to worry about scale.




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I’m always paranoid about fire. Three separate times, three different airplanes, I have walked into a hangar to find a big blue stain and a puddle of 100LL on the floor. The idea of a light bulb or any open heat source scares me. The purpose built(i.e. Tanis) heaters are a different story. Not everyone has the ability, but heating the hangar sure is nice. We keep our hangar at 55* and no engine pre-heat. Power is cheap in Central Washington

scottf wrote:I think if one has the option to kick on the heater when needed the day before it is probably better than leaving it on all the time, but if thats not possible or practical leaving the heat on is way better than no preheat... heat accelerates chemical reactions but i would suspect the air is so dry in most regions where you need preheat that moisture and corrosion are probably pretty small on the things to worry about scale.
...

I don't know what the correct answer is (other than no preheat is the worst thing you can possibly do to a frozen engine), but even in very dry environments there's a LOT of moisture inside the engine case. Short of forced air and a desiccant, I don't know how you'd ever dry one out. I pull my oil cap immediately after shut-down, but I doubt the escaping steam is any meaningful portion of the moisture inside the engine.

If I'm flying two or three times a month, I prefer my engine to stay frozen between pre-heats. (Come to think of it...can rust even occur if the water is frozen?) I don't see any upside to keeping that water warm and condensed on the metal surfaces. Since I'm just flying for fun, budgeting another hour or two for the pre-heat is no big deal.

OregonMaule wrote:Is it bad to leave the engine heater on for 5-10 days between flights? Would this procedure cause more condensation than leaving the engine cold then heating over night before the flight? I use a Aerotherm heater.

Thank you Rob

I agree with Hammer's comments.

An aquaintance and his friend own a really nice C185. Three years ago he told me they "got to" buy a new engine. He said they decided to leave their sump heater plugged in 24/7 a few years prior to our conversation. After a couple of winters their cam was severely pitted and they found corrosion pitting in the top end too. He blamed the corrosion on condensation on the unheated top end. I've read that Tanis and other engine heaters that bring the whole engine to temperature don't have that condensation problem.

Since my engine just has the sump heater and my hangar is unheated I only plug it in a few hours before I fly. I also wrap the cowl & prop with multiple blankets & use cowl plugs to keep the heat in during the pre-heat process. FWIW I've seen advice in Lyc tech notes to avoid internal engine corrosion caused by leaving preheat on continuously. I also preheat my cockpit with a small ceramic space heater for a couple of hours before winter flights. I've noticed my vacuum driven gyros come to life much more quickly when the bearings aren't frozen.

PapernScissors wrote:

OregonMaule wrote:Is it bad to leave the engine heater on for 5-10 days between flights? Would this procedure cause more condensation than leaving the engine cold then heating over night before the flight? I use a Aerotherm heater.

Thank you Rob

I agree with Hammer's comments.

An aquaintance and his friend own a really nice C185. Three years ago he told me they "got to" buy a new engine. He said they decided to leave their sump heater plugged in 24/7 a few years prior to our conversation. After a couple of winters their cam was severely pitted and they found corrosion pitting in the top end too. He blamed the corrosion on condensation on the unheated top end. I've read that Tanis and other engine heaters that bring the whole engine to temperature don't have that condensation problem.

Since my engine just has the sump heater and my hangar is unheated I only plug it in a few hours before I fly. I also wrap the cowl & prop with multiple blankets & use cowl plugs to keep the heat in during the pre-heat process. FWIW I've seen advice in Lyc tech notes to avoid internal engine corrosion caused by leaving preheat on continuously. I also preheat my cockpit with a small ceramic space heater for a couple of hours before winter flights. I've noticed my vacuum driven gyros come to life much more quickly when the bearings aren't frozen.

I think the advantage with an aerotherm heater is that you are heating with warm air rather then probes or a pad. Once you set the thermostat it will just keep recirculating the air at a certain temperature. No different then being in a hangar. And if you crack your cabin heat open I'd bet it'll heat the cabin up as well.

PapernScissors wrote:

OregonMaule wrote:Is it bad to leave the engine heater on for 5-10 days between flights? Would this procedure cause more condensation than leaving the engine cold then heating over night before the flight? I use a Aerotherm heater.

Thank you Rob

I agree with Hammer's comments.

An aquaintance and his friend own a really nice C185. Three years ago he told me they "got to" buy a new engine. He said they decided to leave their sump heater plugged in 24/7 a few years prior to our conversation. After a couple of winters their cam was severely pitted and they found corrosion pitting in the top end too. He blamed the corrosion on condensation on the unheated top end. I've read that Tanis and other engine heaters that bring the whole engine to temperature don't have that condensation problem.

Since my engine just has the sump heater and my hangar is unheated I only plug it in a few hours before I fly. I also wrap the cowl & prop with multiple blankets & use cowl plugs to keep the heat in during the pre-heat process. FWIW I've seen advice in Lyc tech notes to avoid internal engine corrosion caused by leaving preheat on continuously. I also preheat my cockpit with a small ceramic space heater for a couple of hours before winter flights. I've noticed my vacuum driven gyros come to life much more quickly when the bearings aren't frozen.

Well, apparently your friend hasn’t looked at a Continental engine torn down. Unlike Lycoming engines, Continentals locate the cam much lower in the engine, hence that cam is nearly always bathed in oil.

If his cam was pitted that bad, there was something else going on there besides pre heat.

And, yes, Lycoming engines locate the cam in the top of the engine, hence their cams and followers are much more susceptible to corrosion, generally caused by being parked for long periods without pickling the engine.

MTV

That Aerotherm heater kinda cool, though I can't figure out what makes it cost 1 AMU. To the engine an Aerotherm would be equivalent to having a heater hanger so leaving it on all the time would be fine.

My biggest annoyance with engine heating discussions is when someone (in this case it is Aerotherm's website) says they can heat their engine in 30min and be good to go
It takes TIME, like a couple hours minimum, to get the internal engine parts heated and that is what we are really after with an engine preheat. Sure you can blow hot air on your intake system for 30min which will get it warm enough to easily start the engine but will do zero in preventing cold start engine damage.

I plan to install a Reiff preheat on my engine but in the mean time I have a 250W ceramic heater I stick under the cowl and run overnight. I also toss a moving blanket over the cowl. With single digit overnight temps my EGT, CHT and oil temp indications are all in the upper seventies when I arrive at the hangar in the morning.

Sorta related comment: I had a buddy with a big bore snowmobile (1200cc); crazy fun to ride. When left outside overnight in cold temperatures it would take two guy pulling on the rope to get it started. One guy couldn't turn the engine over. Once it was warmed up you could start it with one hand.

whee wrote:...Sure you can blow hot air on your intake system for 30min which will get it warm enough to easily start the engine but will do zero in preventing cold start engine damage....

So...while that's true enough, I'm not entirely positive that a two-hour + pre-heat is necessary, even if it is ideal. My understanding is that most cold-start damage comes from oil which is too viscous and slow to circulate, and pistons and cylinders scrubbing due to them expanding at dramatically different rates as they go from sub-freezing to hot...something exacerbated by the viscous oil not getting there fast enough or in enough quantity.

So if your oil is warm enough to flow freely, and your jugs are warm enough not to bind on the piston...what real difference does it make if the camshaft is still freezing cold? I'm talking starting up, not going to full throttle here.

No argument that warmer is better, but it's often impractical/impossible to get an engine warm all the way through in the field. I routinely pre-heat till the oil and CHT temps are above 50 (and warmer is better), then start up and let the engine warm itself by running...sometimes for a quarter-hour before even doing my run-up. I have no doubt that the internals of the engine are still cold, but I'm at a bit of a loss as to why that matters so long as they're getting proper lubrication?

I'm not a mechanic, so if there's something I'm not getting, it wouldn't be the first time. And before someone brings up the ubiquitous -40 cold-soaked engine and brittle steel, lets keep this in the perspective of most aviators and assume we're dealing with a ten-degree fahrenheit situation or thereabouts. I personally quit flying at -39 degrees:

Before I installed a Tanis system...used a red dragon heater with a 25# bottle of propane and a 12 volt battery. Fed the hot air through the cowl outlet. At -30F and a cowl blanket took about an hour to bring the oil temp up to around 40F... did have to leave a 110 volt heater in the cabin overnight to keep the interior at a reasonable temperature. One problem I had was trimming quickly after take off. The single groove pulley trim system would freeze up. Oh and Tanis has an approved permanent mount cabin heater as part of their STC.


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Hammer wrote:

whee wrote:...Sure you can blow hot air on your intake system for 30min which will get it warm enough to easily start the engine but will do zero in preventing cold start engine damage....

So...while that's true enough, I'm not entirely positive that a two-hour + pre-heat is necessary, even if it is ideal. My understanding is that most cold-start damage comes from oil which is too viscous and slow to circulate, and pistons and cylinders scrubbing due to them expanding at dramatically different rates as they go from sub-freezing to hot...something exacerbated by the viscous oil not getting there fast enough or in enough quantity.

So if your oil is warm enough to flow freely, and your jugs are warm enough not to bind on the piston...what real difference does it make if the camshaft is still freezing cold? I'm talking starting up, not going to full throttle here.

No argument that warmer is better, but it's often impractical/impossible to get an engine warm all the way through in the field. I routinely pre-heat till the oil and CHT temps are above 50 (and warmer is better), then start up and let the engine warm itself by running...sometimes for a quarter-hour before even doing my run-up. I have no doubt that the internals of the engine are still cold, but I'm at a bit of a loss as to why that matters so long as they're getting proper lubrication?

I'm not a mechanic, so if there's something I'm not getting, it wouldn't be the first time. And before someone brings up the ubiquitous -40 cold-soaked engine and brittle steel, lets keep this in the perspective of most aviators and assume we're dealing with a ten-degree fahrenheit situation or thereabouts. I personally quit flying at -39 degrees:

Well, that's well and good, but there's this thing called a crankshaft. It has bearings, and itty bitty holes to permit oil to flow through the crank, depending, of course, on the particular engine.

Point is, there are a lot of parts of an engine that need to be warmed to PERMIT oil to flow. There's oil inside that crank (again, depending on the engine) and a lot of oil trapped in nooks and crannies that isn't going to move unless those nooks and crannies are warmed, and you really, really need to get that oil warm enough to move.

In other words, I agree with Whee. But, it's your engine.....

MTV

For the naysayers, for heavens sake, don’t ever park your airplane in a heated hangar, or on tiedowns at Oshkosh.......that engine will simply corrode away.....

MTV

Next time you preheat note the oil temp on startup and for a bit after while you get organized. If it stays warm then it's likely the engine's innards we're warmed. If it drops lots then the innards were not warmed. I don't have a number but staying above 10*F to freezing would be nice if that's the point of preheating to begin with.

For moisture release after a day's flight when I'm done I like to open and set ajar the oil dipstick. If it's been cold and moisture has collected at the end of the breather then there may be some residual in the crankcase and inside the valve covers. With the cap open air will flow through and moisture can be visibly released. I leave one of the cowl fasteners or access door nearby unlatched to remind that the oil level needs to be checked and the cap closed before the next flight.

Combustion creates moisture and acids. Oils and oil additives are formulated to combat the acid and getting rid of any excess moisture helps.

Gary