This article originally appeared in the Atlantic Flyer.
Whenever the air temperature drops to 20 degrees Fahrenheit, or lower, piston aircraft engines should be preheated before starting. Starts in the 20 to 35 degree range require some precautions to avoid premature wear or immediate engine damage. These guidelines were provided by Jay Wickham, President of Mattituck Air Base, the world's largest independent engine overhaul facility.
"Below 20 degrees, oil may begin to thicken," said Wickham. "This is especially true of the SAE mineral type oils that are used in the first 50 hours after overhaul. They are single weight oils and are the most likely to become viscous. Even the multi-weight ashless dispersent oils begin to thicken when the mercury dips into the teens. Most engines are equipped with congealing oil coolers, and even if the engine has a non-congealing cooler, a termo by-pass valve can force congealed oil directly into the engine. We've seen engines come in here that had catastrophic failures due to improper starts in cold weather."
Wickham reported that at times the engine may appear to be running normally and warming up nicely, but it can still sustain serious damage from lack of lubrication due to restrictive oil flow. Initial oil pressure and temperature readings can be erroneous.
"It's essential to read and adhere to the engine manufacturer's recommendations regarding cold weather operations," said Wickham. "Pre-heating normally takes 20 to 30
minutes to assure that all lines and all parts of the engine are uniformly warmed. Air should be forced up through the bottom of the cowl to reach the oil filter, sump area and intake manifold. Additional heat should be directed over the top of the engine to reach the cylinders and cooler."
Once an engine is pre-heated, it can be started but should be run for 5 to 10 minutes at idle settings, not at 1000 to 1200 rpm. It is essential to check oil pressure, which can take up to 45 seconds to rise into the green. If a full minute goes by without reaching a proper oil pressure setting the engine should be shut down and inspected. It probably needs more pre-heating.
"An important reason for running at low idle is that oil may not have reached all areas requiring lubrication.. even though there may be an oil pressure indication," said Wickham. "A number of parts in the engine are bathed in 'slung' or splashed oil. But a fluid with the consistency of honey doesn't splash very well." Another problem with high rpm warm ups is that some parts expand faster than others. When run at high rpms, piston skirts can warm up and expand faster than cylinder walls, leading to contact with the walls and possible seizure.
Generally, when running with single weight oils, it's appropriate to use 30 weight in winter, 40 in spring/fall and 50 in the summer months.
With adequate pre-heating and taking time to let the engine warm up at slow idle there should be no cause for premature wear and/or damage. "Freezing temperatures require a little planning and patience," said Wickham. "Your engine feels the cold, too."
For more information about cold weather running, contact Mattituck at (800) 624-6680.