highflyer wrote:
Different statements from Lycoming, Cessna Twin Flyer, John Deakin and from you leaves some uncertainty.
Maybe. But we had/have nothing to preheat an engine with nor any service provider who would do that for us. So either it is starting the engine cold or staying home. Again: In over 3000 hours of piston time I preheated once. And I started many engines below 40°F… None of the engine failures that occurred to me was in the least related to cold starting.
If power is available the Tanis and Reiff heaters seem intrinsically safe to me, working in the same way as Peter’s power resistor. There is no fan and the engine itself will limit the temperature to the extent that a thermostat failure, if one is even fitted, would be a non event. And they are a lot easier to fit that the power resistor, as they stick on the sump, and are widely used, so you are using a well known and “approved” product.
Clearly you need very different methods according to whether
The 1st method needs very little power. Probably a 100W bulb will do the job, raising the engine from say -10C to 0C, especially if the cowling has a blanket on it.
The 2nd method needs a lot more power, and either needs a decent airflow (to heat up the whole engine including cylinders) or (if electric) the heating elements need to be distributed all over the engine. One of the products on the US market (mentioned earlier in this thread) is basically a load of resistors with brackets which attach all over the engine.
Not everybody wants to screw bits all over their engine, and a heater with a fan is always a risk because you are relying on detecting the fan failure to avoid it catching fire.
The first method is more dependent on hangar politics. If you look carefully at this post you see the aircraft is on a rotating turntable. Fairly obviously that isn’t going to work with continuous heating.
There are two issues here:
1. Reduction of the alleged wear after starting a very cold engine.
2. Preventing corrosion during long periods of disuse.
Like @what_next (and pace Mr John Deakin), I’m far from convinced that 1. is an issue of concern to those of us who don’t wish to run a safety-critical engine far beyond the factory recommended overhaul period.
But 2. does seem a worthwhile endeavour for those of us who don’t always fly twice a week. We can use oil with anti-corrosion additives (and in that respect I’ve seen no evidence that any third party additive is better than those which are blended into a can of Total or AeroShell), but that’s not going to protect the valve seats or upper cylinder walls. We can also try to avoid condensation. To quote Vaisala:
What causes condensation?
Condensation will form on any object when the temperature of the object is at or below the dew point temperature of the air surrounding the object.
Or we could accept that even engine repairmen need our money to feed their families, so we should ignore the above and just enjoy flying while we can. 
As an afterthought, we don’t need to run the dehumidifier all the time, or even much of the time. We just need a clever guy like Jan (but more hard-hearted) to make a switch with a couple of sensors to turn it on when the ambient dew point approaches the engine temperature.
Then our repairmen’s kids may have to “manger de la brioche”.
Jacko wrote:
Then our repairmen’s kids may have to “manger de la brioche”.
Watt à térrible dèstiné
LeSving wrote:
You have to fly for at least an hour though
Is there any hard evidence for this? It’s a commonly quoted figure but where from originally?
Engine oil temperature rises pretty fast, especially on air cooled engines running at 75-100% power.
Are we really saying that there is still water/humidity kicking around in the engine after, say, 20 minutes at take-off/climb/cruise power???
Jacko wrote:
There are two issues here:1. Reduction of the alleged wear after starting a very cold engine.
2. Preventing corrosion during long periods of disuse.
Well actually there are three and this is a critical one. Which is, the congealed oil in the oil cooler as was reported which can burst the oil cooler leaving you with a dead engine. If you read that article by the people who overhaul and repair oil coolers they give you advice. Conservative yes but still good advice. And who should know better then they?
But Jacko you are right for pointing out and clarifying the issues.
As for point 1 if I haven’t started my engine in two weeks and if the temp is in the 40s I do preheat cause I want the oil to circulate as soon as possible.
LeSving wrote:
By keeping the engine above ambient temperature, if ever so little, one degree is enough, no condensation will occur.
True condensation will not occur but as the 310 article stated having a relative humidity at 85-90% which is not near an ambient/DP spread of zero still caused rusting within 5 days on the non oiled lifters. So it appears condensation is not required to cause the start of the corrosion process just high relative humidity.
What has not been discussed is how the main bearings tolerances will be affected by a propeller conducting cold onto the crank shaft. The closer to the prop the colder and greater chance that that bearing will not have the necessary tolerances. Mike Bush did say a worn out engine tolerates cold abuse better because the tolerances are no longer that tight.
C210_Flyer wrote:
True condensation will not occur but as the 310 article stated having a relative humidity at 85-90% which is not near an ambient/DP spread of zero still caused rusting within 5 days on the non oiled lifters. So it appears condensation is not required to cause the start of the corrosion process just high relative humidity.
Probably, but the thing with heating is it also reduces relative humidity. In a typical European winter it is very easy to get rid of all condensation and lower the relative humidity to safe levels, simply by heating. This will quickly evaporate condensed water also.
Heating 10 degree above ambient at 10 deg C, and the relative humidity is reduced from 100% to 52%.
It is true that to prevent condensation i.e. to bring RH below 100% you merely need to raise the temperature above the dewpoint.
So even a tiny bit of heating in a hangar will make it much more “aircraft friendly” – because the DP will usually be the same inside as outside, after a short while.
But when it comes to the internal volume of an engine, the DP is likely to be different to ambient, at least for quite a while after landing, due to condensation of fumes etc. I don’t know the answer… just making the point that the DP inside it may be higher so more heating may be needed than just a small rise above ambient.
