Cold Weather Operations for Lycoming and Rotax Engines

This article is based on interviews with Lycoming’s Technical Support Rep Brandon Dildine and Dean Vogel, Technical Director at Lockwood Aviation Repair, for questions regarding Rotax engines.

Lycoming Engines

Surprisingly, Lycoming defines cold weather operations as 20° F (-6.7° C) and below. However, performing the following in warmer temperatures will not harm your engine. The advice provided within this article applies to both the parallel and angle valve Lycoming engines.

Lycoming recommends reading Service Instruction 1392—Cold Weather Operation and Engine Lubricating Oil Recommendation and Service Instruction 1505—Cold Weather Starting.

While Lycoming defines cold as 20° F (-6.7° C) and below, it will not harm your engine to preheat it at higher temperatures. Three hours of preheat should be enough for most temperatures. Note, Lycoming does not recommend leaving your engine connected to a preheater full time. The reason is that warm air inside the engine may retain moisture and promote rust.

Why preheat? According to Lycoming’s Dildine, a warm engine is easier for the starter to turn over, the starter uses less amperage to do so, the engine comes up to operating temperature quicker, and it causes less wear on engine components. All good things.

Using a multiviscosity oil can also help the engine turn over quicker because it does not “thicken” in cold temperatures, as “straight-weight” oils do.

Lycoming recommended the following for preheating its engines:

Hot air blowers are considered the best because they heat the entire engine.

Tanis or stick-on heating pads are acceptable.

Only preheat your engine for a couple of hours; do not leave the heater on all season.

Priming an engine prior to a cold start is good; however, Dildine said using the carburetor’s accelerator pump to prime the engine can lead to premature accelerator pump wear. This is because the accelerator pump only works when rapidly moving the throttle from closed to open. Not to mention the risk of an engine fire when using the accelerator pump to prime the engine.

An electrical reel mounted at the front of the author’s hangar makes it easy to plug in an engine heater and battery tender. The air line makes it convenient to air up tires and perform compression checks during the condition inspection.

Now that we have the engine preheated and started, what about cold weather operations?

Dildine said, and the Lycoming Operator’s Handbook confirmed, there is no low limit for oil temps. The handbook states that the engine is ready to fly when you can advance the throttle and the engine does not stumble.

Dildine went on to say:

During initial start-up, the engine should be operated at or below 1200 rpm until it is warmed up, to reduce engine wear.

A maximum oil pressure of 115 psi is the upper limit during takeoff.

Higher rpm can cause accelerated wear, especially on engines with roller tappets.

Installing a winterization kit is a good idea.

You want to see oil temps of 175 to 185° F (79 to 85° C) for cruise operation. Cooler temps will allow oil to accumulate moisture, which will be visible as a white accumulation on the dipstick or under the rocker covers.

Temperatures below 130° F (54° C) are too cold and detrimental to the engine during extended flight.

Minimum CHT is 150° F (66° C) for takeoff.

Oil temperatures of 130 to 140° F (54 to 60° C) prior to takeoff are desirable. If it is so cold that the oil temperature does not warm up but the engine can accelerate smoothly, go fly. Flying is better than sitting on the ground for prolonged engine runs.

If you have an older Lycoming engine with flat tappets, which are defined as tappets without a Diamond-Like Carbon (DLC) coating (released about 2011), add LW16702 additive or equivalent to the oil for year-round operations. This is now recommended for all engines, after break-in. It is also recommended for engines that are running unleaded fuel. Both AeroShell Multigrade and Phillips Victory oils have this additive, or something similar, so you may not need to change how you lubricate your engine.

Rotax Engines

Lockwood Aviation Supply in Sebring, Florida, is arguably the most knowledgeable organization in the U.S. with regard to Rotax engines, and Dean Vogel is its “go-to” guy with regard to Rotax engine operation.

When asked, Vogel said, “Preheat the Rotax engines when below freezing because it is better for the engine.” As for how to preheat the engine, he mentioned the Tanis system or adding a heating pad to the sump and covering the engine with a blanket.

For those with injected Rotax engines, he mentioned that the oil pressure will spike to 90 to 93 psi and drop down to the 30s before coming back up to 55 to 60 psi. While that is a bit unusual, Vogel said they believe it has to do with the design of the oil pressure regulator. He went on to say, “Other than watching for the oil pressure fluctuation during start-up, cold weather operations are not a big deal.”

However, he did add that if you operate in the single digits (Fahrenheit, not Celsius), you should block off the portions of the oil cooler next to the oil fittings to drive the oil temperatures up.

Vogel said he likes to see a minimum oil temp of 120° F (49° C) before going to a high-power setting and 190° F (88° C) in operation/cruise. This will allow any moisture that collects in the oil as a byproduct of combustion to boil off, and reduce the possibility of corrosion on internal parts.

As for when and how long to preheat, he said, “Don’t waste the power keeping the heater on 24/7. Preheat starting three hours before flight. Cold operations are not really an issue with these engines.” He added one advantage to these liquid-cooled engines is that they allow builders to install an automotive-type heater core, rather than using a muff on the exhaust, which may introduce carbon monoxide into the cabin.

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