musings on engine preheat
There are issues of condensation with turning heat on an off if you don't fly once warm. There are issues of uneven heat expansion with just a sump heater. I'm no expert, so don't ask me for details, but you can fill in the blanks.
I am certainly no expert on this subject, just a very interested participant over the last several years, so I will try to fill in some of the blanks. If someone has strong feelings about the engine preheat issue (and
some of the strong feelings I have heard expressed over the years were stated by individuals with
no experience preheating their own plane....) I don't wish to attempt to change their mind. But for the RVer who is exploring this matter with an open mind, I present the following points which I have considered in the six winters I've preheated my RV-6.
1) It is readily accepted by nearly everyone with aircraft piston engine knowledge that starting a cold-soaked engine is bad news in terms of accelerated cylinder/piston wear and potential journal-to-bearing interference.
2) I also subscribe to the school of thought that allowing an engine to go through successive warming and cooling cycles via a heater without flying the engine is potentially setting the stage for abnormal corrosion. That is why my plane stays on the heater continuously once cold weather arrives. I have managed to convince myself (always a dubious process...) that there is less potential of harmful corrosion occuring if the engine is constantly maintained above the dewpoint of the environment.
3) I am not concerned about uneven "expansion" or rates of heating within the engine compartment. As I stated in an earlier post, my plane is housed in an insulated hangar in an area of the world that experiences milder winters than the northern climes. We often see sub-freezing temps, but the temps moderate for brief intervals during winter. It has been my experience that the engine compartment is maintained at a fairly consistent temp if the heater is allowed to stay on all the time. The sump heater I use is thermostatically limited to 150F so the oil won't coke. I routinely see oil temps that are very close to cylinder temps when the engine is ready to start. Placing my hands in various parts of the engine compartment also confirms that there are no significant hot or cold spots.
So....in my case, I think that continuous heating works fine and my engine is safe from accelerated corrosion. I have never seen condensation on the dipstick as I have sometimes seen in unheated engines, and when I had a cylinder off the engine after five winters of heating, I saw no indications of corrosion on the lifters or cam lobes.
I think the key to safe continuous preheating is maintaining a consistent temp engine-wide. In my case, this is possible due to the benign environment of the insulated hangar and plugging in the heater as soon as the plane is returned from a flight. If my plane was in a drafty hangar in a very cold climate, no doubt cylinder heaters would be necessary to achieve the consistent temps thoroughout the engine.
But here is my point. I have often heard blanket statements uttered in a loud and condescending manner about how our engines will turn into rust buckets if continuously pre-heated. My position is.......it depends on the individual circumstance. Tie a plane down outside in a Michigan winter and run only a sump heater with infrequent flying and I bet you will see accelerated corrosion over the years. But keep the plane in a hangar where the temps don't go through extreme swings and I think continuous pre-heating with a sump heater has merit.
One thing is for sure; the Lycosaurus really does turn over nicely and start quickly when it is warm.
Sam Buchanan
My heater:
http://thervjournal.com/cold.html
