When and how to pre-heat your aircraft engine.

Transcript: Video Vignettes - Aeroshell Maintenance Answer Videos II

Preheating: When and how to pre-heat your aircraft engine

 

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[AeroShell Winged pecten]

[Text] AeroShell answers

Ben Visser

Speech: Ben Visser

When and why to preheat your engine are two common questions.

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 [Text] Ben Visser Shell Lubricants

Speech: Ben Visser

Most pilots think the only reason engines are preheated is to warm up the oil. In reality, preheating heats both the oil and the entire engine assembly.

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Ben Visser points to an engine

Speech: Ben Visser

Aircraft engines are constructed from parts made from different metals. These metals have different coefficients of thermal expansion.

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Close up of engine

Speech: Ben Visser

For example, when an aluminum crankcase cools, it shrinks faster than the iron crankshaft that it’s holding. As a result, the clearance in the main bearings decreases. This can cause increased wear if the engine is started at cold temperatures without preheating.

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Ben Visser

Speech: Ben Visser

One way to preheat the engine is through a forced-air system, which forces hot air in through the cowling to heat the engine and the oil. The duration of the preheat depends on the ambient temperature, but you should always preheat long enough to ensure that the entire assembly is warm. The second preheating method is the electrical system.

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Hand points to components in an engine

Speech: Ben Visser

This engine has a system with a heating element on the oil pan and individual elements on each cylinder.

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Ben Visser

Speech: Ben Visser

I’d caution against using a large heating element on just the oil pan. First of all, it doesn’t heat the engine. Second, the surface temperature can get hot enough to cause oil coking. I’d also caution against leaving the system plugged in all the time. This may increase rusting, especially if there’s moisture in the oil. If you have an electrical system,

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Electrical system being plugged in

Speech: Ben Visser

just plug it in for a few hours before flying, or leave it on the night before.

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Ben Visser

Speech: Ben Visser

So, when should you preheat? Engine manufacturers typically recommend preheating any time it’s below 20 degrees Fahrenheit. I would preheat whenever it’s at or below freezing, especially if you’re using a single-grade oil. Another important consideration is the temperature range during the day. For example, if it’s zero at night but warms to 32 degrees by mid-morning, you shouldn’t take your plane out of a cold hangar, start it up and go flying. When the factories recommend preheating below a certain temperature, they’re implying that the aircraft has been completely warmed up to that temperature.

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Camera zooms in on Ben Visser

Speech: Ben Visser

The bottom line is that cold weather by itself is not harmful to your aircraft engine. However, you will need proper preheating and winterisation kits to ensure proper oil temperature. I’m Ben Visser. Good flying.