Engine Pre-Heaters/Preheating Techniques

Greetings Skymaster afectionados! I recently purchased a 1967
T337B. I would like to know if anyone had any suggestions on
a pre-heat system? In my last plane (Comanche 250), I used a
glue-on oil pan heater....I realize this does not address the
crankcase...Also, I would like to say that for a new 337 owner,
this website and message board is invaluable.. I have already
learned mucho.. Thank You very much!
JIM

[FRED-E]

Sorry Jim
I clicked on New Theard instead of Reply. Check "Friendly Web Site"
Fred N358

[Guy Paris]

Hi Jim,
Welcome aboard, no pun intended, I have had the Tanis cyls. case, and oil pan heaters on since about 93. Its even gone from one engine to another. My JPI (engine Monitors) tells me I have 2 cylinders on each engine that need the cyl. elements replaced or repaired some how. I new they were out last winter however there was not that much difference , but noticably less cyl. temp on the 4 cyls. Which reminds me I am going to order some blankets to use when I am out and about, borrowed some up in Northen Maine last winter and was suprised how long the engines remained warm, (several hours). Not having anything to compare to except the heaters that you stick in the inlets, they have been great. Guy....old72driver

[Bob Cook]

The Tannis or glue on sump heaters work great as long as you give them time to work and the AC is out of the wind.

I carry a small honda kw generator and plug them in on the ramp to keep the ac warm. works great if you do not have a plane full of passengers.

If you store the AC outside then you need blankets and "bungs" to keep the heat load down. If really cold then you need prop covers since the prop will "wick" the heat.

I have a pager interface that will turn the tannis heaters on for 6 hrs when I ring the pager. You do not want to leave the heaters on indefinately.

Also you can wire up a electrical box and a switch to put both heaters in series. This way you can leave them on.

Some heaters can "burn" the oil if you are not careful and create condensation at the oil filler neck if the OAT is cold.

I will always preheat one way or another if the OAT is less than 40 deg F. I won't start the engine if below 20 deg F without some form of heat.

Depends where you are located.

Fyi

Bob

[Pat Rolfes]

Bob-

Interested in your comments about not keeping tanis plugged in for more that 6 hours. Once winter comes (here in Des Moines) I keep mine plugged in straight thru. Have for the last 10 years.
Have never heard otherwise. Can you explain???

[Dale Campbell]

I hanger in the mountains of Penna, very cold in winter.
My hanger has insulation & the winter sun sometimes get the inside 10 degrees warmer than outside temp. I picked up two $40.00 ceramic heaters at Wal-Mart. I open the front gear doors with emergency pump handle & pull the gear motor breaker, that's on my 337H model. On front engine I place the ceramic heater on top a metal bucket to gain more height. I cover both front & rear engines with blankets, close off openings in front & rear cowlings with blankets. On rear engine, I place ceramic heater in main gear wheel opening. I set timers to ceramic heater to come on 5 hours before my next flight. When I get there the engines are nice and warm. You can also put a ceramic heater in cabin to get interior up to temp. That way all instruments and controls are also nice and warm.

[Bob Cook]

Believe there is a note in the TCM tsio360 manual and I have heard it elsewhere.

The heater may not have a thermostat and if left on too long it can possibly "burn" the oil. Also the cold surfaces on top of the engine can promote condensation and increased moisture in the oil.

This is not for all sump heaters and does not apply to cylinder head heaters.

If left in all the time then the temp should be controlled and proper blankets over the engine cowls to insure even distribution of heat thru the block.

I would expect the ceramic heaters to do a far better job of heating as it does not promote temp differentials between sump and crankcase housing. No doubt the crank/prop would be a good source of "cold".

Perhaps this is a good explanation // see below for part of the article on corrosion.

http://www.amtonline.com/<br /> sea...%5C1002_01.htm

I will dig up more if need be.


Bob

================

By Gary Schmidt

The debate in the industry has centered around the issue of the sources of these elements as well as the issues of when and why the metal is vulnerable to the other elements necessary for the corrosive process.

First let’s analyze where these elements necessary for corrosion originate. No. 1, moisture: When you burn a pound of fuel, you get about a pound of moisture as a result. Most of this is expelled out of the exhaust stacks but some enters the crankcase via "blow by." Some moisture comes from the air that the engine takes in through intake and it is mixed with the combustion moisture. One other minor source is the moisture in the air that is drawn in through the engine breather tube as the engine cools after shut-down. The aircraft engine absorbs this moisture and doesn’t release it unless your oil temperature gauge gets over approximately 180 degrees F. If you have your oil temperature high enough, the moisture vaporizes and exits by way of the crankcase breather.

Naturally, because moisture is a key element to the corrosion process, engine manufacturers emphasize that aircraft located in coastal areas and areas with humid climates are more susceptible than aircraft located in arid regions. The fact is that there are very few areas of the world where the air is so dry that you do not need to worry about corrosion. Everyone needs to consider corrosion regardless of their geographic location.

Now, where do the corrosive agents come from? This is another area where you will get differences of opinion. In addition to the small amount of corrosive agent found in air, the primary source is the result of the combustion process. When fuel burns, the exhaust gases are corrosive. Some of these gases enter the crankcase via the "blow by" and the corrosive agents are deposited into the crankcase and the oil. You can observe the corrosion caused by exhaust by looking at your aircraft belly behind the exhaust stack. Rivets in this area often corrode.

When an engine oil is exposed to heat, a process called "oxidation" is started. When oxidized oil is mixed with moisture as discussed earlier it often forms an acid which attacks metal surfaces. This is a concern relating to certain sump pump preheaters which may overheat and degrade the oil as it heats the engine. Another problem with these heaters is that as they heat the oil, driving the moisture out, the vaporized moisture will rise and again condense on cooler parts of the engine. This condensed moisture will begin the corrosion process on that engine part.

Another suggestion for operating your engine is to keep the engine running lean or at least do not operate it "full rich" more than necessary. A rich mixture results in unburned fuel left in the cylinder. This unburned fuel with its corrosive agents leaks by the rings and ends up in the oil sump. A properly leaned engine also helps increase oil temperature.

Avoiding "sump only" engine preheaters is another recommendation. These heaters tend to vaporize the moisture in the oil and allow it to condense in the cooler parts of the engine which, in turn, provides the moisture necessary for the corrosion process. Engine pre-heaters that heat the entire engine evenly avoid the condensation problem. Buldoc, the engine rebuilder, also strongly recommends not leaving any engine preheater on for lengthy periods, i.e. days or weeks. Clearly warm air holds more moisture than cold air.

There is another little known product from Tanis Aircraft Services that is designed to deal with engine moisture and corrosion. It is a product patented by Peter Tanis to blow moist air out the inside of an aircraft engine. It connects to the oil breather tube and blows air through the engine out of the oil cap. It works best when the air inside the engine is warm and it has absorbed the moisture created by recent fuel combustion. The humid air is blown out and replaced with dryer outside air. If the outside air is cool, all the better. As it enters a warm engine, either warm by recent operation or warmed by a preheater, the cooler air will absorb more moisture as it warms. The use of the aerator is not recommended if the aircraft is stored in areas where the air is already very humid or where it may contain corrosive agents such as salt which is likely in some coastal regions.

About the author

Gary Schmidt recently purchased Tanis Aircraft Services. You can contact Gary at (320) 634-4773 or by e-mail at Info@tanair.com.

Above is from the URL posted

bob

[Paul Sharp]

I store my airplane outside on the line at the FBO (since hangars are $300 a month around here and they aren't heated, either). I have a '67 T337B.

I've looked at a lot of options, and finally, due to cost, complexity, and convenience, I bought two of those $30 ceramic heaters at Wal-Mart, a little bit of clothesline cord to tie them in place with, a bunch of old blankets at the surplus store, a multi-tap and one 20' extension cord with one 75' extension cord.

If it gets to 10 degrees C then I know I'll have trouble starting the engines; above that I just prime, crank, warm up, and go. I know that bothers some owners, but I consider it a fact of operational life. I know there is some wear and tear on engines to start them cold but as long as they will start, I'll buy the wear and tear compared to all the other expenses - my decision.

What I do with the heaters is: FIrst of all if I can get into a hangar overnight for a warm up I do that since it not only warms up the plane and engines, but gets the snow and ice off as well (that always has to be done one way or another). So when I can do that I don't even use the heaters.

When I do use them, I put them into the opening right alongside the props, tying them in place with the little cords (otherwise they fall and shut off when they're not horizontal). Then I stuff the blankets around the opening to make them snug. I also put a blanket into the scoop on the rear engine. After about an hour or two I can usually start the engines without any problem.

I can keep the heaters, cords, and blankets in two canvas cases I carry with me in wintertime.

I also have a common garden sprayer pump full of ehylene glycol (which you can refill from the deice trucks, usually with no charge - I find the guys just dump a little in from their deice truck and smile and wave). I carry it with me in winter also, because sometimes that's the only way you can get ice off the wings when you're at podunk and there is no hangar, no deicing.

Works for me so far....

[Pat Rolfes]

Bob-

Thanks so much for the info. I'm really intrigued by this one.

My mechanic and his father say they knew Pete Tanis (we're all from central Iowa). They insist that Pete had no problems with plugged in "all the time"(obviously based on weather). He talked of maintaining constant temps vs warm-cold-warm-cold. He felt tanis has enough "uniform" heat that there are not really condensation collection points.

They qualified all of this with me by including that the plane must be flown a "reasonable amount" for this to apply.

Still looking for definitive answers....

[Bob Cook]

Pat

Ultimate solution in order of importance;

1) heated hanger above 75 degrees
2) Somewhere in Arizona out of direct sunlight.
3)store in a large vaccum bag / ie. sandwich bags.
4) fly it every day.
6) sell it.
7) don't worry about it.

Seriously.
You should have EVEN heat on the engine as opposed to just the crankcase.

Only way to eliminate moisture in the oil is to fly it for more than one hour at cruise or better.


Bob

[WebMaster]

Normally, I keep my plane in a hangar, at GRR. It's not heated, but I have pan heaters, and can plug them in. In a week or so, I'm flying out of BDR to take my wife back home. Do you folks suggest that I have the FBO put warm air on the engine before starting, sounds like I should, and how long do they warm it up for?

[kevin]

Best thing is to have them put it in a heated hangar, either overnight, the night before your departure if you can afford it, or for a few hours on the morning of your departure.

I have little experience preheating other ways, so I'll leave that answer to others.

I always preheat when the ambient is below freezing.

Kevin

[Tony Giantonio]

Preheat? Not if you don't want to. But, boy you will pay for it. Anytime the temp gets down around 32 degrees you should have some sort of a pre-heat. Pan heaters are a great way to pre-heat. The heated oil is thin enough to start to flow as soon as the engine starts, thats what its for. If your on the road the best pre-heat is to have the aircraft put in a heated hangar a few hours (min) prefer overnight before your flight. All the components will heat up at the same time. 2nd best pre-heat is forced hot air. Most FBO's will have some sort of pre-heat, but there is a warning here, that some linepersons are not fully trained on how to use it. I have seen blistered paint on many occassions. Have the lineperson put the heat tubes in the air scoop(s) and insure they are secure and directed over the top of the cylinders. One thing about cold oil, even when using pan heaters they heat the pan oil and dont the cylinders, valves, lifters, etc.... that oil, if its real cold is still the thickness of molasses. It will not move too fast or coat the moving parts. Ive heard form the manufactures that it takes aprox 9 min to completely cycle the oil just after start up. Thats along time to wait for complete coverage of all metal parts. In that time there is alot of scraping and gouging going on. Your really wearing out the engine more than normal. So if you don't want to pre-heat don't but don't tell your mechanic I don't know why the engines didn't make overhaul. My recommendation, pre-heat to the best you can always, don't skrimp on the few dollars here.

[kevin]

I agree with all that Tony wrote. One factor he did not mention, if I understand it correctly, is that pistons and cylinders are of dissimlar metals that expand and contract at different rates. At normal operating temperatures, operating clearances are correct, but if the engine is (too) cold, the cylinder is actually too small (having contracted more than the piston), creating increased friction and wear, as well as more difficult starting the colder the engine gets.

Oh, and I am told another risk from hot air preheat done inexpertly is melted electrical wiring.

In case I ever have to have this procedure done on my airplane, can anyone tell me, on an average winter day with ambient temperature of say 15 F, how long should you let them (make them) preheat your engine with a propane heater (sitting out on the ramp). How many minutes?

Kevin

[Tony Giantonio]

Kevin, Your exactly right about the different metal expansion rates when cold. The very reason to have a pre-heat done. Ive seen bent rods due to the oil in the lifters so thick that the lifter didn't move and bent the rod. This is an extreme case for sure. But it shows you should have a pre-heat when the temp gets down to about 32 deg. As to how long to let a propane pre-heat go I don't think that there is a general rule of thumb for this. You have to look at how the FBO is doing the pre-heat. What type of pre-heater is he using. I've seen quite a variety of systems from electric/kerosene torpedo's ducted with two hoses to the airscoop, to the "Flame" portable propane heater, which is very good unit easy to use, and finally the herman nelson big units army/airforce surplus. They all put out heat at diferent rates so its real hard to judge how long to let them run. The FBO may be your best source for how long to let it run. If I was to venture a guess, I would let them pre-heat about 30 min checking often on progress. Yes you want to be there while there doing the pre-heat. You have the time while getting flight plan completed so thats the time used to make sure no damage is being done to your airplane. One thing to check is that the cowl flaps are open allowing the heated air to move someplace. The air should move as if the plane is in flight in and out. Hope this helps alittle. Tony G.