Preheating

How to keep the Cessna 170 flying and airworthy.

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170C
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Preheating

Post by 170C »

This is my month to ask lots of questions :wink:

I have heard a lot of comments regarding when to preheat our Continentals and how long to do so, etc. Some say its not needed unless the temps are below 30 f. I like to keep mine warm below 50 or so with 50 wt oil. It sure starts easy on those mornings when the outside temps are in the 20's. Some have cautioned against leaving heat on the engine all the time. I have a small electric heater with a thermostat and have it connected to some clothes dryer duct so the heated air goes up the bottom of the cowling opening. Just wonder if doing so is creating any potential problems? If what & why?
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mit
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Re: Preheating

Post by mit »

Come on up to Fairbanks this month and I will show you how. :wink:
Tim
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GAHorn
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Re: Preheating

Post by GAHorn »

Frank, my personal opinion is that continuous heat from direct contact heaters is both unnecessary and potentially harmful because it can accelerate rust/corrosion.
I also use the method you mention (ducted hot air) but only for a few hours or overnight immediately before an expected flight. The big concern is a heater that allows the temp to increase...then decrease....then increase...then decrease... with the potential for the cooling-off period to introduce condensation. (Warming the engine warms the air inside the engine. When the engine temps then drop to a lower level the air cools and re-enters thru the crankcase vent tube, drawing moist air back inside the engine. Then re-warming the engine condenses that moisture on the walls of interior parts and the moisture drains down into the oil and settles at the bottom of your sump and causes rust on other exposed parts like cyl. walls, etc., before it expels air again... then the engine cools again and the cycle repeats.
Therefore, I recommend you use the method you described...but only when it's necessary to warm it up for an intentional flight... not continuously.

PS: I also stick upside-down small ( 3 oz.) Dixie paper cups into my exhaust tailpipes to prevent moist air and insects from entering my exhaust and into any cylinder with open exhaust valve. The throttle is kept completely closed to reduce air entering thru an intake valve. (If forgotten, the cups blow off at engine start.)
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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170C
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Re: Preheating

Post by 170C »

So George, even though my heater probably runs constantly this time of the year, you feel it still allows the engine to cool off enough to develop condensation?
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Re: Preheating

Post by GAHorn »

You said it was on a thermostat....which I imagined it cycles on-warm/off-cool, etc.?

Be alert also to that electric heater sitting on the hangar floor where gasoline vapors pool.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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170C
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Re: Preheating

Post by 170C »

Heater sits on a moving dolly with a milk crate on it so there shouldn't be a fuel vapor issue although anything is possible. Regarding the thermostat, yes it can slow down or speed up depending on the temp, but even on fairly warm days (temps in the 50's) it is running. I will likely stop leaving it on continously and turn it on the evening prior to a flight.

You mentioned the crankshaft seals-------Is it possible that a one piece seal could be replaced by a so called two piece one? I had assumed all of our engines used the same type.
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Re: Preheating

Post by GAHorn »

Chances are your original seal was also a "split" seal. The split was installed so that it's split did not match the crankcase split.
Yes, any nonsplit original seals were designed to be lubricated/slipped over the prop flange and the springs disconnected/reconnected. The split seal is a replacement seal type, and you remove the spring, twist the seal to slip it over the crankshaft behind the prop flange, then reinstall the spring by hooking it back together. Then push the seal into position with sealant.

From the Ovhl manual: " Remove spring from new crankshaft oil seal. Twist seal, and pass it over the shaft race behind the prope~ler flange, with lip to rear. Coat seal lip and shaft race with Gredag #44. Pass the spring around the shaft, and hook the ends. Lift the spring progressively into the seal groove. ..."

Next, be certain the split in the seal is at least 20-degrees offset from the crankcase split. I recommend you pre-lube the seal inner surface with engine oil if you don't have "Gredag #44" to make certain it does not wear excessively during first start up.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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170C
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Re: Preheating

Post by 170C »

I appreciate the info regarding the crankcase/crankshaft seal (as well as the other answers to my questions)
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Re: Preheating

Post by flyboy122 »

Pokey,

Most A&P's will vehemently recommend not preheating the engine unless you are going to fly. If you heat it all the time condensation forms in the engine causing rust and corrosion. Apparently a winter of this can ruin an engine. One of the guys at work was at an FAA IA seminar a few years back when they pulled out some crusty parts caused by a winter of constant preheat. It's not a myth, it really happens.

The exception to this rule (there is always at least one! :) ) is that if your heater gets the temp warm enough, and keeps it warm enough, to cook off the condensation then constant heat is ok. Depending on the ambients, this may take a good heater and some insulation around the cowling.

Personally, I'm not chancing it. I'm working on setting up a cell phone activated switch that will turn my heater with a text message. I can get a prepaid el cheapo phone for a few bucks a month, so the cost is minimal. Have everything plugged in and ready to go after each previous flight, then a couple hours before I want to fly, I call the phone, and when I arrive at the hanger my plane will be all ready to go!

DEM
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pdb
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Re: Preheating

Post by pdb »

Preheating is necessary but it need not be a huge problem. I am tied down outside all winter in Anchorage. If you have access to eletricity, all you need is a good insulated engine cover and two electic interior car heaters with internal fans like these.

http://m.napaonline.com/tablet//parts/P ... 0331540245

Or

http://www.oreillyauto.com/site/c/detai ... &ppt=C0192. (Try Amazon too.)

I put one inside on the bottom of the cowl and use a little bridle made of safety wire to hold it in position. It hooks over the edge of the cowl where the exhaust exits the cowl. The fan circulates the warm air all over the interior engine compartment. It warms up the oil, crankcase, cylinders, battery , etc, In 20°F weather, two hours appears more than sufficient. The engine cover does a good job of trapping the warm air.

The other heater rests on the floor right in front of the pilot's seat with the fan pointed towards the underside of the panel. I usually place it on two aluminium chocks that rest on the floor to keep it off the carpet. The interior, including the instruments, warms nicely and the canopy defrosts.

Its almost like having a hangar until its time to get the wing covers and residual snow and ice off.

I have one of each heater. The Napa model has a plastic body, is a bit thinner, and fits easily into the cowl. The Zerostart has a more robust metal case and I use it for the floor heater. I think it would fit under the cowl as well but I have not measured it.
Pete Brown
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N4563C 1953 170B
http://farm3.staticflickr.com/2366/2527 ... 4e43_b.jpg
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GAHorn
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Re: Preheating

Post by GAHorn »

Here's another / similar product for $10.. : http://www.harborfreight.com/12v-auto-h ... 61598.html
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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pdb
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Re: Preheating

Post by pdb »

The Harbor Fright heaters are only 150 watts... might be ok for defrosting the windshield with a light frost, I doubt they will do much compared to the 900W units I use as noted above.
Pete Brown
Anchorage, Alaska
N4563C 1953 170B
http://farm3.staticflickr.com/2366/2527 ... 4e43_b.jpg
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GAHorn
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Re: Preheating

Post by GAHorn »

Yes... I posted the wrong link.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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blueldr
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Re: Preheating

Post by blueldr »

George,

When I saw that comment and the HF 150 watt heater, I realized you were talking about pre heating in Austin, TX, on the fourth of july.
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Re: Preheating

Post by hilltop170 »

pdb wrote:Preheating is necessary but it need not be a huge problem. I am tied down outside all winter in Anchorage. If you have access to eletricity, all you need is a good insulated engine cover and two electic interior car heaters with internal fans like these.

http://m.napaonline.com/tablet//parts/P ... 0331540245

Or

http://www.oreillyauto.com/site/c/detai ... &ppt=C0192. (Try Amazon too.)

I put one inside on the bottom of the cowl and use a little bridle made of safety wire to hold it in position. It hooks over the edge of the cowl where the exhaust exits the cowl. The fan circulates the warm air all over the interior engine compartment. It warms up the oil, crankcase, cylinders, battery , etc, In 20°F weather, two hours appears more than sufficient. The engine cover does a good job of trapping the warm air.



The other heater rests on the floor right in front of the pilot's seat with the fan pointed towards the underside of the panel. I usually place it on two aluminium chocks that rest on the floor to keep it off the carpet. The interior, including the instruments, warms nicely and the canopy defrosts.

Its almost like having a hangar until its time to get the wing covers and residual snow and ice off.

I have one of each heater. The Napa model has a plastic body, is a bit thinner, and fits easily into the cowl. The Zerostart has a more robust metal case and I use it for the floor heater. I think it would fit under the cowl as well but I have not measured it.
I agree with Pete, I have been using two of these car interior heaters for years and have always had good luck with them used as Pete describes.

I have tried just about every type of external pre-heat there is from weed burners, Red Dragons, catalytic heaters, light bulbs, and Herman Nelsons. The small auto interior heaters work the best of all of them. I carry both heaters, a splitter power plug, and 300' of arctic extension cord in a small zipper bag. Unless you are totally remote, there is always power available somewhere.

Permanently installed Reiff bands, bayonet cylinder head inserts, and bonded-on heat pads unquestionably are the absolute best for pre-heat in cold country where it is a regular procedure but for occasional use, the car interior heaters work great.
Last edited by hilltop170 on Wed Jan 21, 2015 2:33 pm, edited 3 times in total.
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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