Section I: Equipment and Environment

Part IV, Chapter 12: Preheating Equipment and Methods

Engine Compartment

Aviation fuel is distilled with a much lower vapor pressure than automobile fuel so that during the climb to altitude engine failure will not be experienced due to vapor lock. What this means from an operational point of view is that once temperatures get down to about 15 degrees F/-9 degrees C, the engine will require preheating so the fuel can properly vaporize for ignition.

Compounding the problem, at about -5 degrees F/-21 degrees C most oils (the exceptions being synthetics like the discontinued Mobil AV-1) become too thick to lubricate the cylinders and bearings properly, and if you could manage to start your engine at this temperature (by heavy priming, or a bit of mild preheating), the wear that would take place until the oil began to flow would probably be equivalent to more than 50 hours of normal operation.

(Mike Busch, the Cessna Pilots Association's engine specialist, claims that one cold start at the lower temperature extremes can cause as much wear as 500 hours of normal cruise operation. This takes into consideration the metal-to-metal contact between the piston and cylinder walls caused by the uneven expansion of the aluminum pistons and steel cylinders as the engine goes rapidly from very cold to very hot.)

If you have a turbocharged engine you are well advised, even when using multi-grade oils, to preheat below 30 degrees F/-1 degree C: the turbocharger is very oil-critical. As for non-turbocharged equipment, preheating is mandatory for Continental and Lycoming piston engines below 10 degrees F/-12 degrees C. I preheat all my engines, turbocharged or not, below 30 degrees F/-1 degree C: I like to get my full TBO.

There are no convenient ways around these problems, and, like the FAA and taxes, they are a fact of aviation life. In this chapter we will take a look at the best methods available to both the remote-area bush pilot and the city-based airport pilot when operating under daily conditions that require preheating. However, before doing so, let's continue our examination of a piece of equipment (mentioned in the previous chapter) that is necessary to both areas: the insulated engine cover.

Engine covers

Now made out of nylon like our wing and windshield covers, engine covers are padded with about an inch of synthetic insulation and are designed to fit snugly over the engine cowling, fastening with Velcro strips, nylon ties, and bungee cords (see illustrations 28 and 29). Used properly, they also serve a number of related uses during the cold, stormy months of winter.

Electric heaters

In "Ye olden days" bush pilots often used little 750 watt "car warmer" heaters that cost about $20. These heaters typically measured about 4"x6"x7" and contained a metal heating element, a temperature-controlled safety switch, and a small fan. One or two placed in the engine compartment after the last flight of the day, with the cowling then covered by an engine cover, did a fine job, and they were the standard until the fine Tanis preheat system came on the market. Now the car warmers are mostly relegated to the cockpit, where they help keep it and the instruments warm.

The Tanis preheating system is a light-weight (one to two pounds, depending on application) system of thermal pads that attach to the crankcase and oil pan, along with heater elements that attach to the cylinders. In the better installations, a flush-mounted power receptacle is installed in a non-structural skin area (such as an engine baffle) on airplanes like the Super Cub, Cherokee Six, or Bonanza that have cowlings that open easily for pre-flight inspections (see illustration 30). On airplanes like the C-180/185/206 where you have to use a screwdriver to get the cowling open, a flush plug door, similar to the ground service plug receptacle for an external power source, is installed. The standard Tanis TAS-100 system is good down to about -30 degrees F/-34 degrees C; the Tanis "Super System," which I use, is good down to -65 degrees F/-54 degrees C. Recommended highly.

An emergency technique

Sometimes a pilot will get caught away from home base without his combustion preheating equipment, but will have electricity available. Here the thing to do is borrow a droplight (using a 100 or 150 watt bulb) from the local maintenance shop and place it in the engine compartment. With the engine cover in place, this will keep the engine warm indefinitely as long as the temperature does not drop too far.

Combustion heaters (in the city)

Combustion heaters range from the large Herman Nelson and space heaters used by FBOs for transient aircraft (for prices ranging from $25.00 to $40.00 per engine) to the small portable units used by the bush pilots. All these unites need to be used wisely, for applying just enough heat to get an engine started once it has been cold-soaked overnight is a fine way to damage it, and bring on an early overhaul.

Combustion heaters (in the bush)

Preheating an engine in a wilderness environment demands that your combustion heater be dependable, durable, and portable.

For dependability, avoid anything too fancy or complicated, including those cute (and expensive) little blower heaters operated by a 12 or 24 volt DC motor that are designed to be hooked up to the airplane's electrical system. In conditions of deep cold, these will often not work due to a cold-soaked battery.

For durability, avoid most of the camp stoves now on the market. These are designed for the weekend camper; they usually lack quality construction and are not something you would wish to stake your life on.

For portability, choose a heat source that is small and light enough to be carried in the airplane's winter survival kit (see Chapter 24). This is important, for the professional bush pilot will every now and then find himself stuck overnight someplace due to a fast-moving weather system and will require the services of his engine preheater once the front moves through.

The best bush preheating rig is one that uses a simple old-fashioned gasoline blowtorch that can be operated on avgas taken directly from the airplane's fuel sumps. Since this is a systems approach, if you wish to use a different heat source you will find little difficulty in adapting this technique to your purpose. For the convenience of those who are unable to locate gasoline-powered blowtorches -- they are hard to find these modern days -- several alternative heat sources have been listed, though they all fall far below the level of utility that the blowtorches achieve.


While the engine compartment is the primary area we have to preheat -- for VFR flight it is the only area that is truly necessary -- we do have to consider the cockpit. Besides comfort, the reasons for this are:

  1. In airplanes that are to be operated at night or in IMC, including whiteouts, radios and gyros must be at or above their minimum operating temperatures. With panel-mounted radios and indicators -- HSI, RMI, VOR, etc. -- this is usually -4 degrees F/-20 degrees C; with pneumatic gyros, -22 degrees F/-30 degrees C. (The slaved remote DG and flux detector that drive the King KI 525 HSI and KI 229 RMI are certified to -66 degrees F/-54 degrees C).

  2. Windshield condensation can often be quite severe at very low temperatures, when defroster efficiency is impaired for the first few minutes of the flight. A little heat, just enough to remove cold-soaking, will go a long way towards resolving this problem.

I use one or two 1500 watt electric "car warmer" heaters in the cockpit. In the city, where electricity is available, I plug them in the night before, at the same time I plug in the engine preheater. In the bush, at my base of operations, I use a small electric generator to operate the heaters, turning them on at the same time I start preheating the engine with blowtorches.

In this way, by the time the plane is ready to go, the cockpit and instruments are warm enough to be operational.

(Tanis manufactures a panel instrument heater system, which I have never tried because I prefer heating the whole cockpit with a car warmer, but I imagine it works as well as the rest of their equipment.)

Away from my base, in the bush where no power is available, I have to content myself with VFR until the cabin heater has warmed the radios, indicators, and gyros to their operating temperatures. This usually works out okay, for low temperatures in the bush, away from the cities and their dense blankets of ice fog, usually mean VFR weather.


Cold also affects the battery; at seriously low temperatures it will not have enough power to start the engine. In the city, when electricity is available, many pilots with C-180/185s and Super Cubs will use a simple battery heater, such as the one sold by Tanis, or put a small "car-warmer" heater in the battery compartment. Pilots with airplanes like the C-206 do not need to bother, for the battery is in the engine compartment and will be kept warm by the engine heater as long as the engine cover is in place. In the bush, however, things are different, and you must either remove the battery and take it inside for the night so it can be kept warm, or you must handprop the airplane for the first flight of the following day.

[Please Note: The next Chapter, Chapter 13: Cold Weather Engine Operations, is unavailable on the web. The online edition continues with Section I, Part IV: Introduction: Navigation Tips (Silk Scarf to High Tech).]

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