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Preheating: why and how.

Over the years, there have been almost as many myths and wives' tales about why and how to preheat an aircraft piston engine as there are people telling you how to land. Let's try to separate some fact from fiction.


The primary reason to preheat an engine is to help ensure adequate lubrication as soon as the engine starts. Cold, congealed oil doesn't flow very well and greatly increased wear can occur in an engine until its oil is flowing smoothly. At the same time, the different alloys in the engine expand and contract at different rates. In extreme cases, close-tolerance components like bearings can contract with cold to eliminate any clearance between it and a crankshaft. Not only is this guaranteed to increase wear but it also prevents oil from flowing in the first place.


Too often, we've seen a preheat session involve about 20 minutes of blowing propane-heated air into a cowling. That warms up the cylinders - maybe--along with the accessories, but doesn't do a thing for the oil. As this article's main text notes, aiming the heat source at the oil pan is critical to ensure thorough heating.


Our preference is to use a slower, steadier method--which can be gas or electric--overnight. In any case, use a blanket, like the one pictured at top. Gas preheating systems like the one pictured in the middle photo definitely work faster than electric ones, but also can be cumbersome to transport and handle. Then, there's that pesky problem of carrying five gallons of propane in the cabin.

Instead, we prefer an installed electric system using heating bands around the cylinder bases, as pictured at bottom, plus at least one heating pad attached to the oil pan. This type of preheat system is simply plugged into a 120-volt AC source and allowed to work. Since it's already installed, there's nothing to lug around, except maybe a drop cord and a blanket, there's a very low hassle factor. The only better preheating systems we've found is a heated hangar or staying out of cold weather.




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Title Annotation:AIRMANSHIP
Publication:Aviation Safety
Geographic Code:1USA
Date:Jan 1, 2012
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