It's always a good idea to preheat your plane before you head out for a flight on a cold winter day. But how should you preheat your plane? And when should you do it?
Here are three of the most popular methods.
1) Heated Hangar
We'll start with the best option: a heated hangar. Why is putting your airplane in a heated hangar the best? Because everything is the same temperature. Your engine, oil, avionics, seats, everything is the same temp.
Pulling your plane into a heated hanger starts the warmup process immediately, but it also takes the most time. How long is that? Depending on how cold your plane is, it can take up to 8-12 hours for everything to reach hangar temperature. But even if you only have a few hours, you'll get the warmup process started, which is better than nothing.
An issue with heated hangar space is that it can be hard to find. And if you do find it, you may need line personnel to move other planes out of the way to make room for yours.
Pros: The most even heating you can get.
Cons: Not always available. Takes the most time.
Cost: Many FBOs will rent overnight heated hangar space for $50-$100 per night.
2) Electric Heater
Another great way to preheat your plane is with an electric heating system. There's only one catch: your plane needs to have it installed.
Tanis Aircraft Products makes the most well-known electric preheaters, but there are several others on the market as well.
The preheaters work by attaching electrical heating elements to the cylinders, oil pan, and crankcase of your engine. When you plug the system into an outlet (they make them for 115V and 230V), your whole engine starts the slowly warm up. It's not an instantaneous solution, but if you leave it plugged in for an hour or two, you'll have a fairly warm and happy engine. For maximum warmness, Tanis recommends that you leave the system plugged in for at least 6 hours to reach 'thermal equilibrium'.
Pros: Easy to use. Heats evenly if you give it enough time.
Cons: Not installed on many airplanes.
Cost: Starting at $700 per system.
3) Forced-Air Preheater
If you ask for a preheat at your FBO, chances are they'll use a forced-air cart. These carts are usually powered by diesel, gas, or propane, and they can kick out quite a bit of heat. Almost all of them vent the engine exhaust separately from the air going through the heating tube, so it's safe to use them to preheat your engine and your cabin. After all, while the goal is to have a warm engine, having toasty seats (and avionics) is a good thing as well.
There are a few problems with forced-air carts, however. First, they don't evenly heat your engine, and you'll typically find that the front of the engine ends up being warmer than the back. When you have engine parts at different temperatures, it also means that they have expanded (or contracted) at different rates as well. This can lead to more wear-and-tear on startup.
The second problem is that if you need a preheat, chances are somebody else does too. That means that unless your FBO has several forced-air heaters, you could be waiting in line to use it, and your time to use it may be limited.
When is my engine warm?
This is one of the most difficult questions with a forced-air preheat. Because different parts of your engine will get different amounts of airflow, it takes time to get everything up to temperature.
Lycoming's service instruction No. 1505 says this:
"Apply hot air directly to the oil sump, external oil lines, cylinders, air intake, oil cooler and oil filter in 5 to 10 minute intervals. Between intervals, feel the engine to be sure that it is retaining warmth. Also check to be sure that there is no damaging heat build-up. During the last 5 minutes, direct heat to the top of the engine."
Here's what Continental's service information letter SIL 03-1 has to say:
"Proper procedures require thorough application of preheat
to all parts of the engine. Hot air must be applied directly to the oil sump and external oil lines as well as
the cylinders, air intake and oil cooler. Because excessively hot air can damage non-metallic components
such as seals, hoses, and drives belts, do not attempt to hasten the preheat process."
"Apply preheated air directly to the oil sump, oil filter, external oil lines, oil cooler, coolant radiator and cylinder assemblies.
Continue to apply heat for a minimum of 30 minutes."
Pros: Available at almost any cold-weather FBO.
Cons: Doesn't heat evenly.
Cost: $15-30 per preheat. Sometimes free if you purchase fuel at the FBO.
When Should You Preheat?
Now that you're ready to preheat your plane, the last question is, when should you do it? Most pilots and mechanics agree that when the temp drops below 32F, it's a good idea to preheat your plane. And when the temp drops below 15F, you should always preheat if possible, to keep everything running smoothly.
Just remember, if you need a winter coat to preflight, your plane could probably use a preheat.
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