Cold temperatures cause the oil to freeze and sap the battery’s strength, which can lead to overworking and potential damage to the starter and engine. For this reason, many aircraft manuals, pilot operating handbooks (POHs), and engine manufacturers advocate specialized cold weather starting techniques, which include preheating the engine and ensuring that the aircraft uses an oil adapted to the temperature.

The correct oil is the first part of the equation. Some flight schools notify their instructors and renters when the school has performed the seasonal oil change and go so far as to lock up the off-season oil.

Oil thins when heated, thickens when cold, so it is important to have an appropriate weight. The second part of the equation is making sure the oil has the necessary viscosity to flow out of the crankcase and back into the engine when the starter is engaged. If the oil is too thick to move, engine damage may occur.

Engine builder Lycoming offers written advice on Cold Weather Starting which includes the warning: “Improper starting in cold weather may result in abnormal engine wear, reduced performance, shortened time between overhauls or engine malfunction.

The use of preheat will make starting in cold weather easier and is necessary when the engine has been allowed to drop to temperatures below (plus-)10 degrees Fahrenheit /(minus)-12 degrees Celsius ((plus-)20 degrees F /( minus)-6 degrees C for (minus)-76) series engine models.”

That’s good advice, according to JD Kuti, owner of Pinnacle Aircraft Engines in Silverhill, Alabama. Kuti, a powertrain mechanic, has 15 years of experience working with piston engines and has seen the damage caused by improper starting in cold weather.

“When the engine sits, the oil freezes, it always settles in the crankcase,” Kuti said. “In cold weather (40 degrees F and below), the oil is very thick and takes longer to penetrate the entire system, causing wear.”

Kuti said mechanics sometimes see engines where the crankshaft has been pulled forward during engine cranking when there is no oil in the area. “This can cause the engine to produce metal,” he said.

Lack of oil isn’t the only thing that can damage an aircraft engine. Shrinkage of dissimilar metals used in engine construction can cause problems.

The crankshaft, for example, as well as the connecting rods and cylinders are made of steel or chrome for greater strength, while the pistons as well as the crankcase and cylinder heads are made of aluminum to save weight. Repeated contractions and expansions can weaken these parts. One way to avoid this is to ensure that the aircraft engine temperature remains within a specified range when the aircraft is on the ground.

If you do not have an air-conditioned space to park the aircraft, but it is parked in a hangar with electricity, you may want to invest in a repositionable electric heat source that is placed inside the engine cover and left on when the aircraft is not in use. These units are thermostatically controlled and can be left on overnight or all the time.

In colder climates, such as Minnesota in the winter, many aircraft owners use a device like this in conjunction with cowl and propeller covers and a blanket to keep heat in the engine compartment. Heat transfer occurs by convection and conduction, which reduces the risk of fire because there are no open flames or glowing elements.

There are several manufacturers of engine preheaters. Reiff preheatingfor example, advises customers that sealing and insulating the engine compartment with a cover greatly improves the efficiency of an engine preheater, as does the use of foam hood plugs.

Air heater notes that its devices do not require permanent installation in the engine and can therefore be shared, for example, as part of a flight school fleet.

E-ZHeat has a system that resembles a heating pad for the oil pan. Place it inside the engine hood, plug it in and let nature do its work.

For aircraft owners who wish to have a preheating device installed, Tanis plane manufactures preheat kits for Lycoming, Continental, Rotax, Jabiru, Jacobs and Austro engines. The company has been around since 1974 and, according to its website, was the first to develop aircraft engine preheating systems for piston engines, helicopters and turbines and received FAA supplemental type certification .

Some preheaters have the added feature of remote activation, so you don’t need to go to the airport to start it. Preheat Remote is a feature that allows a rider to activate preheat via a cell phone app.

Whichever one you choose, note the manufacturer’s recommendations for how long the engine preheat should be on before flight. Also heed the warnings about letting it run too long, as this can cause moisture to build up in the motor and lead to rust.

Pilots should respect the one-hour rule, Kuti said. “Preheat one hour before flight. Do not fly if you cannot fly for at least one hour, and open the gauge for at least one hour after flight to allow steam to escape from the engine,” a- he declared.

Regardless of the type of preheat applied, pilots should refer to the POH or Aircraft Flight Manual (AFM) for cold weather operations specific to their aircraft. This includes warnings not to “over-throw” when trying to get it started.

“If the engine does not start on the first few attempts, or if the engine’s ignition intensity decreases, it is possible that the spark plugs are frosted,” according to Lycoming. “Preheat should be used before attempting another start.”

Lycoming echoes this warning, noting that if the engine has not started within five seconds, stop trying to crank it and obtain an auxiliary electrical source because the battery is too weak to start the engine.

Pilots are trained to monitor power settings and oil pressure during all engine starts, but especially in cold weather. Excessive engine power and low or no oil pressure are a recipe for damage.

Additionally, POH/AFM can encourage extended warm-up time on the ground to allow oil pressure to stabilize before attempted flight. If the engine runs rough, oil pressure and fuel flow fluctuate, or manifold pressure is excessive, these are good indications that the aircraft engine is not properly warmed up.

Airplane owners can get very creative when trying to preheat their plane’s engine.

You may know someone who has built their own external system. This may include a hot air blower powered by electricity or propane and ductwork, such as a washing machine hose, to blow hot air directly into the engine hood.

It’s important to direct the air so that it doesn’t damage the wiring or pipes, which means opening hood louvers if they exist to prevent heat from building up too much.

If the flight school does not have a preheater, pilots, especially flight instructors, can get creative.

On one occasion we removed the electric heaters from the ground school classroom and placed them in front of the plane and, using chairs and a blanket, made a sort of tent above the hood which trapped the hot air inside.