Why not the cowl flaps, so the warm air can raise up through the cowling?
+1 on a blanket / old sleeping bag to keep the warmth in – just don’t set it on fire!
tmo wrote:
Why not the cowl flaps, so the warm air can raise up through the cowling?
Yes. That’s better.
Engine will be more equally warm. If you put hot air up in the inlet it may not fully reach the bottom (oil sump).
I would have thought that when warming an engine one should seek to heat the metal parts faster than the oil and water in the sump – so as to minimise condensation.
But down here on the sun-kissed “Scottish Riviera”, we have little experience of cold weather. 
We are talking about preflight preheating which takes just 30-60 minutes. You may disregard the condensation. Good oil flow at startup is what counts to minimise engine wear.
Big NO to overnight heating without good dehumidifier.
Hot air up the cowl flaps/bottom opening is more effective. However, carelessly doing so may result in an engine compartment fire (which I have seen twice). Up the cowl flaps is also better because there also should be an engine blanket on the engine, which should close off the cowl air inlets. As heat rises, and you would like the whole engine to get warm, apply the heat to the bottom, and let it rise through the core of the engine. Tanis cylinder head heaters are a nice idea too. But if the engine is well covered by a blanket, and the heat can soak in, a good oil pan heater will heat the whole engine over time.
The hot air heaters are last generation. All manner of heating machines (most involving fuel and fire) from professional Herman Nelson’s to cobbled together VW heaters. It’s time to retire these for private GA use, and install a Tanis or similar electric heaters. There are good stick on heating pads now, and I have them on most of my machines and my Lycoming. (You have to sand the Lycoming oil pan nice and smooth with a vibrating sander, to get them to stick well). If electricity is not available where the plane lives, very small generators are not expensive.
Thank you – makes sense.
I am thinking an electric forced air flow heater or two (two cowl flaps on my plane) + a remote starter. Given that while the air is hot, it is not “running engine” hot, a risk of fire should be minimal. Must find some reasonably heat-resistant blanket material.
That said, I wonder how much time is needed for a cold-soaked engine to reach reasonable temperature…
From my experience, with a good, well fitting insulated engine blanket, a 300 watt on engine heater will warm the engine enough to start on a -10C day in 3 – 4 hours. If it’s -20C, I’ll leave it on overnight before a start.
About 45 minutes to one hour will make it super toasty with a WDH 2kW heater. A survival blanket on the cowl and an old horse blanket on top of it work well for insulation. Remember to plug your intakes…
Peter wrote:
With another winter here, I came across this from Reiff preheaters.
Does anyone know the best place to buy the Reiff preheater system in Europe, or should I just leave to my mechanics to source and install.
