Mattituck owner has sage advice on preheating

Whenever the air temperature drops to 20F or lower, piston aircraft engines should be preheated before starting.

Starts in the 20 to 35 range require precautions to avoid premature wear or immediate engine damage.

These guidelines are provided by Jay Wickham, president of Mattituck Air Base, the world's largest independent engine overhaul facility.

"Below 20, oil may begin to thicken," Wickham said. "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 dispersant 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 thermo bypass 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 said 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," Wickham said. "Preheating 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 preheated, it can be started but should be run for 5 to 10 minutes at idle settings, not at 1,000 to 1,200 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 preheating.

"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," Wickham said.

"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 rpm, 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 preheating 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," Wickham said. "Your engine feels the cold, too."

For more information about cold-weather running, contact Mattituck at 800-624-6680.


Reprinted from Flyer, Oct. 15, 1999 issue