Preheating is important for three reasons:
1. To protect the engine from damage during cold starts.
2. For easier starting.
3. To reach operating temperatures faster.
What type of damage occurs during cold-weather starts?
A cold-soaked aluminum case contracts more than the internal steel parts, causing excessive engine wear. The cold engine won’t have proper clearances between the case and the bushings, and will experience excessive wear or even a “spun bushing.” Air-cooled engines usually have a built-in cylinder choke to allow for expansion during operation; the cold affects the choke built into the cylinders. This is why it is important to preheat the entire engine and not just the oil.
Why is a cold engine hard to start?
The oil is thicker and the aluminum case constricting the crank and camshaft means the starter has to work harder. Spark-plug frosting may occur if air is introduced into the cylinder but it doesn’t fire right away. A cold engine is also subject to fuel streaming due to the cold temperatures, which is another reason to heat the cylinder heads. Just heating the oil or heating the cylinder base is typically not enough because the design of the cylinder, with aluminum cooling fins around a steel insert, inhibits proper heat transfer to the cylinder head.
In addition to the heads, warming the oil is essential for proper viscosity and proper lubrication of internal moving parts. It can take several minutes for oil to flow to the rocker covers in a cold-soaked engine. Imagine the amount of wear this alone might cause! Some propellers or other gearboxes, such as those on turbine engines and helicopters, are also dependent on warm oil for proper operation.
To properly preheat an engine, an internal electric preheater that addresses both the oil and the cylinder heads is best. “Flame throwers” use indirect heat so they’re far less energy efficient when comparing watts to BTUs; additionally, they’re not portable and may be dangerous to use. Many people don’t wait long enough to heat the entire engine, and only heat the heads so it starts easier, but the damage potential may still exist. In cold, windy areas, aircraft owners should use an insulated cowl cover for more efficient, uniform heating of the engine. A propeller cover is also advisable as the propeller is a large heat sink attached directly to the heart of the engine.
In addition to engine preheat, cabin and instrument preheat is also recommended in more extreme conditions to prevent bearing damage in gyros.
Preheaters don’t cause corrosion. Corrosion may occur over an extended period due to improper engine storage. This is because water exists in an internal combustion engine as a natural byproduct of combustion. In a warm engine, the oil coatings thin out over time, whether from the sun or from preheat. For this reason, leaving a preheater plugged in continuously isn’t advised unless the aircraft flies at least once weekly. Cycling a preheat on and off with a thermostat or timer isn’t advised due to the potential to “drive” water into undesirable areas. Plug them in at least four hours prior to flight or overnight for best results. A dehydrator product would work well in conjunction with the preheater for prolonged periods between flights.
For 35 years, Tanis Aircraft Products of Glenwood, Minn., has been providing cold-weather protection for aircraft.
The company offers summer and winter covers to protect aircraft from the elements and to complement preheat systems. Additionally, Tanis provides a dehydrator product for those airplanes that don’t at least once a week; for long-term storage, Tanis produces a “pickle” kit. To learn more, visit www.tanisaircraft.com or call (800) 443-2136. Jeff Jorgenson has accumulated hundreds of flight hours in experimental aircraft, Pipers, Cessnas and vintage taildraggers over the last dozen years, about half of which have been spent in the cold winters of the Midwest. He has worked in various weather, technology and aircraft industries.