If you live in the northern climes — specifically where the outside air temperature dips below the freezing mark — then you are probably familiar with engine heaters. These little units do a single, simple task: they pre-heat our aircraft engines, so that the engines will start when needed… and not self-destruct in the process.
SELF-DESTRUCT? How can that be, asked a local pilot, who in spite of sub-zero temperatures insisted he didn’t need an engine heater. I told him of the experience of Peter Tanis, the late creator of the Tanis Engine Preheater, and what Tanis found when he tested aircraft engines.
Tanis noted that aircraft engines were designed to get rid of heat, which is what made getting them warm when it is cold outside so darn difficult. Thinking about this statement makes perfect sense — air-cooled engines use air for cooling — duh! Tanis then went on to explain what happened when engines were cooled down to sub-zero temperatures. Since the engines were assembled when temperatures were normal, say in the area of 70 degrees F on average, the clearances in those engines were set in those normal temperatures. Here is the rub (pun intended) — when the engine temperatures decrease towards zero and below, the clearances between the bearings may close to zero.
WHAT’S THE BIG DEAL? WON’T THE ENGINE STILL START? Sure it will, but when it does, the bearing … lets say the #1 piston connecting rod bearing … will be locked on to the crankshaft. When you turn the starter, what would normal slide will not, and that could mean a spun bearing in your engine. Spun bearings will reduce your overall oil pressure in the short term, and may cause the engine to fail in the long run, since the fixed bearing in the connecting rod will start to wear the connecting rod hole out until you can’t maintain oil pressure, or something breaks!
Oil is also affected by cold temperatures — even today’s high-tech, multi weight versions. In some models of the Lycoming engine, cold oil temperatures could mean that your valve guides on the furthest cylinders from the oil pump will run unlubricated for a minute or three. This means immediate damage to the valve guides, which need oil to stay cool and relatively low in friction.
LISTEN TO THIS LESSON WELL — IF YOUR ENGINE IS COLD, MAKE SURE IT GETS PREHEATED. How much preheat is enough? While Mr. Tanis has a system that will heat the engine perfectly in just about any situation, the fact of the matter is that if you can heat up your cowling and keep it warm for three to four hours, you will be able to warm your engine up to the point where it is safe to start. For owners of the Tanis System, at least an hour of soaking is needed.
GAS OR ELECTRIC? Either will do, but remember that your chance of a fire is higher with a gas heater that has an open flame. Any fuel leak or seep with an open flame is a bad combination! In some remote areas, only gas heaters can be used, due to a lack of electrical power, so pilots in such a situation have to maintain ZERO TOLERANCE for fuel leaks.
COVER YOUR ENGINE. Remember — your engine and cowling is designed to dissipate heat, not keep it in. Putting a cover over your engine, even if it is an old, unused quilt or sleeping bag, will help keep heat in, and in doing so, help your engine get up to the right temperature faster than if you did not cover the engine.
BOTTOM LINE: Engines are expensive. In the winter months, a proper job of preheating your engine is required in order to preserve that expensive resource, so that it stays running for you in good times and bad, in winter and summer, in rain and in CAVU weather. The engine keeps the prop spinning, and the prop keeps you cool. If you disagree, try stopping the prop while you are in flight … bet you start sweating!