A hairdryer poking into the engine cowling for half an hour works a treat for me (and I'm starting from -20C).

A quick google....

Here

4. COLD WEATHER STARTING. During extreme cold weather, it may be necessary to preheat the engine
and oil before starting. [no values given]

This famous Lyco flyer says (page 15 of the PDF)

For most Lycoming models, preheat should be applied anytime temperatures are at 10˚ F or lower. The exception to this rule is the 76 series models that include the O-320-H, and the O/LO-360-E. These engines should be preheated when temperatures are below 20˚ F.

and uses the word "guideline". 10F is -12C and 20F is -6C.

Then you have piles of "urban knowledge" e.g.

here

Never attempt a start below freezing without pre-heating

Assuming they mean freezing point of water, that is 0C.

If somebody finds a current Lyco document speaking of mandatory preheating below +6C I will eat my EDM700 :)

This is an interesting product.

Ignorant? I spend plenty of time in EASA-land, as well as numerous other jurisdictions, too. You're correct: my maintenance qualifications are FAA certification, and I'm quite content to operate within those bounds.

You do not require a field approval, however, to operate a combustion heater, which will easily fit in the trunk (or "boot") of your car.

There's more than one way to skin a cat, more than one way to wet a duck (and it's backside), and more than one way to preheat an engine. The manufacturer recommended method involves a heated hangar. In lieu thereof, other methods are available.
Reiff makes an excellent product.

This may not be directly applicable to most engines people are flying these days, but as a matter of academic interest, let's not forget two more techniques fairly popular in the past:
- If the engine has an easily accessible drain cock, drain the oil while it's still warm, come back next morning with a pail of preheated (+50...60C) oil.
- At the time of shutdown, dilute the oil with avgas. While you are starting the cold engine, this will reduce the oil viscosity; as the engine warms up, the fuel will evaporate and the oil will return to its normal viscosity. Radial engines are often equipped with an oil dilution valve directly in the fuel system. Many winters ago, when it suddenly got as cold as -30C, I used this technique on my UAZ. With undiluted oil, the starter would barely crank the engine even with a warm battery, so it had to be towed for a few minutes to get started. A cupful of petrol into the oil in the evening would allow me to start in the morning without any problems. (Once again, this should not be construed as an endorsement of this method unless allowed by the manufacturer; Lycoming explicitly discourages it).

Draining the oil overnight, and oil dilution have already been addressed. Draining oil is a start and addresses the oil, but doesn't address the need for preheat, with or without having prepared the oil.

Oil dilution is a function of mixing a lubricant and a solvent and does result in chemical changes to the oil, as previously discussed.

Radials have used oil dilution in some cases, but so have horizontally opposed recip engines. With good reason, this option is no longer offered in airplanes such as the Cessna 206 (where it was once a common option), and oil dilution has been removed or deactivated in nearly all light airplanes.

Well, it will obviosly vary from engine to engine, but a bucketful of hot oil + some careful cranking may be enough to bring the engine to its starting temperature if it isn't very cold outside.

BTW, speaking of external combustion heaters... Just a couple of weeks ago, a Mi-8 helicopter in Russia was destroyed by fire after an explosion of the ground-based heater. If you use one, always have a fire extinguisher within easy reach.

IO540

Something we find useful in the North country, especially for automobile doors, is WD 40 spray. We open the doors and spray it on the latch and inside door jam. This prevents doors from sticking/freezing.

hope this helps

Always have a fire extinguisher handy during any engine start.

Dry lube silicon spray does the same thing. It doesn't attract dust or leave residue that can attractdust or dirt.

Took me five attempts at getting logged on this site..think I am unwelcome.

Why not just stick to the Lycoming handbook. If you have to preheat take the machine where you can use a popane fired 230/110V space heater on the front end and do it that way.

Of course I realise a lot of people who own these machines are not artisans. It is going to cost you money what ever you do.

Preheaters which involve a lot of hot air work well, as long as they are properly used. If the hot air involves actual fire, it is obviously very undesireable in the engine compartment. I have ferried for repairs two aircraft which had wiring fires in the engine compartment, bacause of the over zealous use of "propane" heaters.

Unfortunately, one of the three areas of the engine, the crankshaft area, is also the deepest in the engine. Cylinders and oil sumps are relatively easy to preheat by various means, but it takes a long time for heat to warm the crankshaft.

I use the proper electric oil sump heater, and switch in on for at least three hours before I fly. The heat rises well from the oil sump up, and throughout the cowl, and warms the whole engine. Those who blast in a whole bunch of hot air (least effectively into the upper cylinder area) for a "short" duration (less than 30 minutes) are probably fooling themselves. That heat has had little effect on the crankshaft, which is the most expensive part of the engine to be turning over with ineffective lubrication.

Slow and easy does it best.... like so many things in aviation....

A blanket around the cowl, with the heat inserted under the engine using scat hoses, over the course of several hours, works well. I've seen people burn the paint off cowling on light airplanes by attempting to put too much heat in too fast, especially through the inlets at the top of the cylinders (where it doesn't do much good.

Heat rises, of course, and allowing the engine to warm from the bottom, up, means that the entire engine eventually gets warmed. Manufacturer recommendation is to allow at least 5 hours for proper preheat, when using forced air.

I have also seen pilots cause leaks or damage seals by starting in cold weather and cycling a propeller full of cold, congealed oil.

Pre-oilers are good investments for those operating in cold weather, but rearlly are a wise investment for those operating in any kind of weather. Interestingly, they're not seen very often, any more. A preoiler circulates oil before the engine start, throughout the engine, to prelubricate (and warm) the engine. They're also useful for post flight shutdown lubrication and cooling.

Hot air rises, and there is usually plenty of it on this forum. Heat radiates conductively via the path of least resistance.

Actually, heat transfer by conduction, convection, and radiation are entirely different processes.

In the case of preheating an engine by forced air (external combustion heater), one is initially using the convection process for heat transfer, then relying upon the conductive properties of the metal.

In a given medium, heat conductivity relates to the thermal resistance of the material. The second law of thermodynamics provides that heat transfer is from the point of highest temperature to the lowest. One will heat the engine the most thoroughly and the fastest by heating from beneath, rather than above the cylinders, and allowing convection and conduction to transfer the heat upward, rather than down.

Heat in oil rises, heated air rises, heat in the engine rises, and yes, when conducting heat through the engine, including the application of heat at the sump, heat rises. The lower portions of the engine will be the first to cool, and should be heated first. After shutdown, the lower portions of the engine cool first, or fastest. Even in operation, the upper portion of the cylinder and upper spark plug tend to receive the greater heat, which is part of the reason that airflow through the cowling is directed at the upper half of each cylinder in a horizontally opposed installation, with airflow generally being aft and downward from there, in a pressure cowl installation.

SNS

Yes. Basic physics education for blue collar kids was lost in the UK around 1968. We now have a whole generation of people who had the money but not the understanding. They did the couse but knew SFA once they had passed the exam. This is part of the issue with the UK. They make up their own rules then invent the reality to match. You are not alone.

DAR

Tell em as it IS! They need a heater. Happy Holidays!

Not unless you are melting it, it doesn't!

Complete tosh. The molecules of metal in the engine are not free to move about like air or water (or other fluids, e.g. molten metal) and change density.

Therefore there is no lowering of density, and no heat rising in the metal of the engine.

If you are able to show me bubbles of pistons rising through denser, cooler cylinder heads then I will believe that metals can heat via convection!

FBW

To be fair, by heating the bottom of the engine, the outside air around it will presumably receive some heat too and then rise, transferring some heat to the top of the engine by convection.

Whether the amount of heat transferred this way is significant, compared to the amount of heat transferred internally by conduction, is debatable, but could be enough to make bottom-up heating preferable to top-down.

If we're getting all scientific about this, does anyone know the heat capacity of engine oil. We always put a 1kW fan heater inside the cowling and under our 0-200 for 30 minutes before a very cold start but I would be surprised if it had much effect on oil temperature.

We use it to warm the carburettor and induction system so the petrol vapour stands some chance of getting up to the cylinders before condensing (no primer, just an accelerator pump). With sufficient sucking in it always starts immediately after being in an unheated hangar at about -5C. Sometimes it stops again just as the oil pressure is coming up and, although it restarts with a couple more primes, I've never understood why.

Don't know about yours but an IO540 is about 160kg total weight, excluding externally mounted accessories and the exhaust. Of this, the oil is only about 8kg.

The crankshaft is probably the heaviest single item, at about (I guess) 20kg. The rest is all the various bits; some are ally, some are brass, and probably most of the weight is steel.

Taking a very average specific heat capacity as 0.7 (kJ/kg/K) this means that 100W (actually transferred into the engine mass) would make its temperature rise by 3C per hour.

I hope I got that calculation right :) Obviously it ignores heat losses from the engine, which will start to occur as soon as its temperature rises above ambient.

That is quite slow, but it probably represents the top end of what can be achieved by poking a heated probe down the dipstick hole.

If the dipstick heaters damage the oil they must be of crap design. On my engine, with 9 qt of oil, the bottom 3"-4" of the dipstick is immersed. If the dipstick hole is in a large pool of oil, then convection will easily carry away 100W, with a temp rise of the order of 10C in the immediate vicinity of the heater. If the dipstick hole is tight around the dipstick then heat will be efficiently transferred into the crankcase by conduction through the layer of oil. The important thing would be for the heater to be temperature controlled (which I guess none of them are) and to heat only the fully immersed portion. The most worrying thing would be if the heater breaks off; the engine will then have to be dismantled to get the bits out :) :)

And 100W might be what actually ends up in the engine from a 1kW fan heater poked up the cowling.

So to do it effectively, from really low temps like -10C or colder, one needs a lot more than 100W.

Fly-by-wife

Exactly - I am afraid our friend Mr Guppy has always had a rather umm, colourful imagination.

Fly-by-Wife
 

"The molecules of metal in the engine are not free to move about like air or water"

As I said you can PAY for an education and still be ignorant. You are an arts graduate maybe? HS cert? GED maybe?

So tell me FBW what exactly DOES move inside the metal. You can use any model you want as an illustration. The one I use was draughted by Niels Bohr in 1911. It is graphic..it has a pic usually..so I guess you should be able to grasp the idea.:ugh: