Engines must be preheated, so that the engine oil is well above freezing, and the cylinders are warmed at least a little, very cold oil is “stiff” and creates a much greater load for the starter and battery. Cold batteries have a lesser capacity, and will be discharged faster – and observe starter motor limits. Common limits are: Crank for 30 seconds, rest for a minute, crank for thirty seconds, rest for more than a minute, crank for thirty seconds, rest for thirty minutes – for a warmed engine. Starter load greater for a cold engine, so limits should be reduced.
The additional benefit of preheating the engine, is that you’ll preheat the vacuum pump too. If it has any water in it, which freezes after the last flight, and is not warmed, it can be frozen for your next (non preheated) start) and shear the plastic driveshaft, I’ve changed a number of them for this for unaware pilots.
If the type has a winter kit, it should be installed for winter flying, including a possible oil cooler baffle, to allow the oil temperature to come up at altitude. (Then be absolutely sure that the entire kit is removed for warmer flying. At the top of descent (particularly if you have not installed the winter kit) maximum rate of power reduction is 1" of MP per minute to prevent shock cooling – so plan you descent a long way back.
There’s a lot to know for safe winter flying, and it is rewarded by magnificent air, and better performance! My coldest takeoff was a 172 ferry flight from central Quebec decades back, good preheat with engine blanket overnight, then early morning start at -41C. It warmed up during the flight home, no problem.
It did not get very cold in the Alps but around Normandie we saw -8C
I have engine heater (I did not use it) and also when we went to the mountains we also left aircraft without covers in the cold…this is likely to be a good explanation on the vacuum pump failure, thanks for the tip !
The additional benefit of preheating the engine, is that you’ll preheat the vacuum pump too. If it has any water in it, which freezes after the last flight, and is not warmed, it can be frozen for your next (non preheated) start) and shear the plastic driveshaft, I’ve changed a number of them for this for unaware pilots
I had one surprise this morning:
We flew yesterday to visit friends. Evenings, during the party, a front with rain passed, and then temperatures dropped below zero.
Today we found our Europa covered by ice thick enough to consider the airfoil not laminar anymore. We proceeded with defrost by using warm water, cloth and wiper. The final cleanup we delegated to the rising sun, delaying our departure for about half an hour. Smooth sailing through the still air, with the blue sky reflected in the ponds of the Southern Czechia was the reward:
Our airplane is always hangared except of when touring, so this was a first experience of this kind. But this surprise was also hopeful – can we really get temperatures below zero this winter?
The final cleanup we delegated to the rising sun
Sometimes better leaving things to sort themselves 
Reminds me of the flooded hot starts in summer: leave it that way, grab tea in clubhouse, after everything gets spilled and evaporated, the engine starts on first attempt…
My father keeps saying that cold temperatures are the death of GA engines. We Got recently a Rotax-driven microlight that had a nice day out on snowy runways and about-10 degrees Celsius that is now leaking heftily water and oil.
Bad luck? My father’s a bit, eh, let’s call it disappointed, because he’s got to fix it.
Must be the temperature change because when I fly in typical FL120 or higher temperatures are typically below freezing and that doesn’t seem to hurt.
I am glad that my steed is in a quite warm corner of the hangar. I maintain RPM as low as possible after startup. And hope that it’s not too bad in the end.
What do you think: Would you keep the oil level lower in winter so that it gets warmed up more quickly?
UdoR wrote:
What do you think: Would you keep the oil level lower in winter so that it gets warmed up more quickly?
Certainly not. Preheat the engine, and it will not be a problem. Use an oil cooler baffle if specified for the type to allow the oil to reach the high 100’sF as it should. Use cowling baffles which may be specified for the type, and/or use cowl flaps correctly to assure proper cylinder cooling. Avoid rapid power changes, particularly rapid power reductions at high speed. With this cautious operation, the engine will be fine – as far as it knows, it’s operating normally, so normal oil quantity is appropriate.
Pilot_DAR wrote:
Certainly not. Preheat the engine, and it will not be a problem.
I agree. We use oil sump heaters and have no problems even when starting at -20°C. Well, that’s with Lycosaurs – we don’t have a Rotax (yet).
It is interesting how in countries where it is airfield-politically normal to have plug-in preheat, lots of people seem to regard it as essential In Europe, most can’t due to politics (no power allowed in the hangar) or due to hangar shapes. I knew a guy in Dortmund who had it but he was in a long (wide) shallow hangar where the planes could be moved without interfering with the cables, but that’s not normal.
Also the published oil temp range is pretty wide, with W80 going a lot further down than most would think. I used to run W80 all year but have gone back to 50% 15W50 due to some valve issues.
Peter wrote:
It is interesting how in countries where it is airfield-politically normal to have plug-in preheat, lots of people seem to regard it as essential
Some years ago, a workshop was tasked with installing an electric oil sump heater in one of hour aircraft after an engine overhaul. (The heater is glued to the engine and can’t be removed for overhaul without damaging it.) The shop failed to do so, despite saying that they did and even signing off the installation on the work order!
The electrical installation was already in place so there was no obvious way for a pilot to notice that the heater wasn’t there. We used the aircraft for one winter season without heating while everyone thought the heater was in place. This was not noticed until the spring.
Later in spring, the aircraft had a prop strike and the engine had to be shock-load tested. When it was taken apart all cylinders showed damage which was arguably caused by repeated cold starting. We have not seen such damage on any other engine nor on the same engine when it was overhauled earlier.
So yes, I would say that preheating is essential when you operate for extended periods below freezing.
