Engine Heat

How to keep the Cessna 170 flying and airworthy.

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Engine Heat

Postby 170C » Sun Oct 18, 2009 1:03 pm

Reading an article in EAA I saw it mentioned that it isn't good to have the engine heater go on and off due to the condensation it can cause. I have a small heater that has a thermostat & with some ducting that sends heated air up under the engine and I have a moving pad that I place over the cowling. This permits the engine, and to a limited extent the instruments in the panel, to be heated. Of course here in north TX we don't typically have really cold weather, but I like to have heat on the engine anytime the temp is under 40-50. My question is am I better to leave the heater set to come on each day/night when the temp drops to that level or is it best to have it come on only on the one or two days that I am likely to go fly.
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Re: Engine Heat

Postby jrenwick » Sun Oct 18, 2009 4:11 pm

Hi Frank,

I have a Reiff preheat system on my 170. Here's their FAQ page, related to leaving the heat on continuously (it's OK to do that): http://www.reiffpreheat.com/FAQ.htm#QA3. It refers to an Aviation Consumer article that might have more to say -- I haven't read it.

I used to be a member of a flying club here that had five Lycoming-powered Cessnas with Tanis heaters, and they plugged them in whenever they were in the hangar. They've done this literally for decades with no ill effects.

When I had my 170 in a cold hangar, I put the Reiff system on a timer to warm it up for the weekend (I was working then, and did all my flying on weekends. I didn't fly every weekend, so sometimes I was heating the engine for nothing (i.e. cycling the heat). I started to see rust in my oil filter, so I stopped doing that. When I bought the Reiff system, they recommended turning it on twelve hours before flight, then leaving it off until the next flight.

I'm now in the habit of removing the oil filler cap after each flight, so that condensation can escape. As long as you're not worried about bugs and things getting in there, I think that helps keep the engine clean. I don't know for sure, but it might have helped when I was cycling the heat -- but I wasn't doing it then.

Now I'm in an insulated hangar with radiant heat. In cold weather I keep the thermostat set at 46 degrees when I'm not there, and I don't preheat any more unless I RON somewhere. That's about the best compromise I can think of.

So my recommendation to you is either to leave heat on the engine full-time (maybe just a light bulb inside the cowling, in your mild climate) or warm it only before a flight.
John Renwick
Minneapolis, MN
Former owner, '55 C-170B, N4401B
'42 J-3 Cub, N62088
'50 Swift GC-1B, N2431B, Oshkosh 2009 Outstanding Swift Award
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Re: Engine Heat

Postby hilltop170 » Sun Oct 18, 2009 5:04 pm

Frank-
In Alaska, it is common practice not to pre-heat until the ambient temp falls to 20°F. With the oil technology of today, oil will provide good lubrication at colder temps than in the old days as long as you use the correct grade for the temps you operate in. There are not many days in Texas that go below 20°F when you would be willing to fly anyway, so it's probably not a real issue for us.

It is the cool down side of heat/cool cycles that causes condensation to form in the engine. A constant temperature will inhibit it. In your unheated uninsulated hangar, natural heat/cool cycles can't be avoided so some condensation is going to form. The solution to excess condensation is to go flying more often!

I agree with John, if you are going to fly on weekends and it is going to be really cold, stop by the hangar Friday night on the way home from work and plug it in. Then if you don't go flying, stop back Monday and turn it off. In North Texas we rarely actually need pre-heat. I would not leave it to cycle on and off all the time.

Enjoyed seeing you and Becky yesterday.
Richard Pulley
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1951 170A, N1715D, s/n 20158, O-300D
Owned from 1973 to 1984.
Bought again in 2006 after 22 years.
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Re: Engine Heat

Postby gahorn » Sun Oct 18, 2009 5:50 pm

From TCM SIL03-1:

Warning: Do not leave an engine-mounted pre-heater system on for more than twenty- four hours prior to flight. Continuous operation of engine-mounted preheater systems may result in aggressive corrosive attack internal to the engine

Here's the entire document:

SIL03-1 Cold WX PreHeat.pdf
(380.09 KiB) Downloaded 101 times
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Re: Engine Heat

Postby jrenwick » Sun Oct 18, 2009 9:22 pm

gahorn wrote:From TCM SIL03-1:

Warning: Do not leave an engine-mounted pre-heater system on for more than twenty- four hours prior to flight. Continuous operation of engine-mounted preheater systems may result in aggressive corrosive attack internal to the engine

I'm sure that's an oversimplification, hence the words "may result." I can easily see it happening if you have a heating pad on the sump and nothing else: water evaporates out of the oil in the sump, condenses on the cold upper crankcase and cylinder walls, runs back down into the sump, etc. etc. But not all engine-mounted pre-heaters are alike, and I believe some are specifically designed to solve this problem. TCM's warning may not be the last word.

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Re: Engine Heat

Postby gahorn » Sun Oct 18, 2009 10:26 pm

I think it's easy to read and remember what one wishes to ...and forget what one doesn't want to remember. A quote from the Reiff article regarding the other report directly contradicts Reiff's assertion: "But as they said, it's not definitive, so it's not reasonable or prudent to assume that you can never get corrosion in an engine if the preheater is left on continuously." (Underline mine)

Reiff also says: "Removing or loosening the dipstick or oil cap may also help to reduce internal moisture by ventilating the crankcase. As the moist air in the crankcase is heated by the engine heater it will rise and escape out the dipstick tube, and dryer ambient makeup air will enter through the oil breather line. "
Reiff quotes TCM and Ben Visser as condemning the continual-heater method...then makes every effort to suggest that those two must not include the Reiff system in their recommendations. ("Notice neither Continental nor Shell make any distinction as to the type of engine heater used (multi-point vs. oil heater only), or whether an engine cover is used or not.")
Rather than believe those two failed to exclude the Reiff-type system...I believe they deliberately did NOT exclude any particular system becuase their advice is valid for all systems. Reiff has no evidence to exclude their system from TCM's recommendation and only scant suggestion to indicate that Visser may not have included their system.
Reiff offers a download of the TCM storage Service Bulletin 99-1 as their "authoritative" resource. The opening statement of that SB is: "There is no practical procedure that will insure
corrosion prevention on installed aircraft engines." ...which precludes using engine-heating sytems for that purpose.
I don't subscribe to the theory that keeping outside air circulating thru your engine is a good idea. Unless you are willing to install dessicant-dehumidifiers on the entrance points of the engine, circulating air will continuously introduce moist air. (Yes, if it's below freezing there will be less moisture in that air...but there will still be moisture present in most interiors of bldgs and hangars.) I believe it's best to prevent the exchange of air in stored engines. Their idea of allowing the interior air to exit immediately after shutdown makes even less sense to my way of thinking. If you have a hot engine...then you have a drier atmosphere within that engine. Opening the cap may let that escape but it will allow fresh, moist air to enter via the breather pipe. It seems to me that now you have introduced moisture which you will allow to cool down and condense.
The Lycoming Service Bulletin which Reiff offers as an authority on the subject directly contradicts Reiff and specifically states: "Preferably before the engine has cooled, install small bags of desiccant in exhaust and intake ports and seal with moisture impervious material and pressure sensitive tape. Any other opening from the engine to the atmosphere, such as the breather, and any pad from which an accessory is removed, should likewise be sealed."
I seal my engine against air exchange during storage. My throttle is closed and my exhaust pipes are plugged with upside-down Dixie wax-paper cups. When it's below freezing I preheat with a hot-air blower for several hours. (I also noticed that Reiff considers Mattituck, the TCM overhauler, as an important authority. The Mattituck article to which Reiff refers states, " Air (warm air) should be forced up through the bottom of the cowl to reach the oil filter, sump area and intake manifold. Additional heat should be directed over the top of the engine to reach the cylinders and cooler.") One of the most-oft-overlooked pre-heating tasks, in my opinion, is the importance of heating the oil within any spin-on oil-filter. Unless that oil is warm and not congealed, one runs the risk of collapsing the pleated-paper element, by-passing the element, and/or sending previously filtered dirt through your engine. Spin on filters are usually only warmed adequately by hot-air systems.
Obviously, this is a very personal view.
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Re: Engine Heat

Postby jrenwick » Sun Oct 18, 2009 11:44 pm

The manufacturers clearly have to hedge what they say about this, because they can't control what goes on in someone else's crankcase. But there are examples (I mentioned one) of people leaving aircraft plugged in full-time with excellent results. My example was with Lycoming engines, on aircraft (two 182RGs, two 172s, and one 152) that each had 12 owners on average, so they aren't flown only on weekends -- although, this being Minnesota, they all probably go a week or two at a time without use in periods of lousy or frigid weather. How often you fly might be the most important variable.
John Renwick
Minneapolis, MN
Former owner, '55 C-170B, N4401B
'42 J-3 Cub, N62088
'50 Swift GC-1B, N2431B, Oshkosh 2009 Outstanding Swift Award
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Re: Engine Heat

Postby HA » Sun Oct 18, 2009 11:59 pm

must be that time of year again so here we are at the same old topic :lol:

our flight school plugs in the airplanes anytime they're not flying once the temp is below about 20F, of course those airplanes also fly a lot so they're doing the best thing which is running the engines.

I don't get to fly my airplane a lot but I want to be somewhat ready when I might get a chance, so I'll plug it in (Reiff with a Tanis engine cover inside an unheated t-hangar) even up to a couple days ahead of when I might be going. I figure once it's up to temp it's like the engine is sitting in a 70-80F day. I don't freak out about the engine rusting away all summer, so why should I if it's at a constant temp during the winter.

I haven't seen any increased rust particles in the oil in the couple of years since I've been doing this, of course I only have a screen but I stick a magnet in the oil as it drains in a poor man's oil analysis attempt.

your mileage and opinion may vary, just saying what I do. I'm much happier having the preheater than trying to start it cold.
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Re: Engine Heat

Postby 170C » Mon Oct 19, 2009 1:29 am

Thanks for the vrs opinions. Looks like there is no "best" method so I suppose I will continue to put my ceramic heater/duct under the cowling opening turn the thermostat so it comes on only when it gets pretty cold (north TX wise) and only on the weekends unless I know I am going to fly at other times.

Richard, good to see you too yesterday. Hope you get back from the northeast in time to get to Reklaw!
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Re: Engine Heat

Postby jrenwick » Mon Oct 19, 2009 2:12 am

Frank,

There's a guy in my chapter who sells a remotely-operated electrical switch, based on pager technology. You make a call from any phone, send a page, and your equipment turns on or off. It can control up to three different things. Because it's based on a pager rather than a cell phone, the montly cost is pretty low. If you're interested in something like that, I'll ask him for his contact info.

John
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Re: Engine Heat

Postby hilltop170 » Mon Oct 19, 2009 4:18 am

I have operated O-470 and O-300 engines in Texas and Alaska for the last 26 years, summer and winter.

My C-180 sat outside from 1983 to 1996 summer and winter. I used propane pre-heat and electric but only before a flight, not full time. When the engine was torn down in 1996 it had NO rust anywhere inside the engine.

My C-170 sat outside from 1983 until 2006 summer and winter. While I did not own the plane, there were several periods of 6 months at a time when the engine was not started. When the engine was torn down in 2006 it had NO rust inside the engine.

I do not think the Continental engines have a significant problem with rust based on what I have experienced.

I would use the pre-heat system that is most advantageous to my situation and not worry about it.

Frank- Weather permitting, we should be back in Texas on Thursday or Friday.
Richard Pulley
2014-2016 TIC170A President
1951 170A, N1715D, s/n 20158, O-300D
Owned from 1973 to 1984.
Bought again in 2006 after 22 years.
It's not for sale!
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