Re:  Engine Heaters Cast as Bad Ideas

Yesterday, I had an in-depth conversation with one of the most experienced people in the best engine shop in the Midwest.  He said that he had come to the conclusion that engine heaters were causing excessive engine corrosion.  He stated that they could tell by the corrosion where the engines had the heaters placed, even--i.e., head heaters, sump heaters, etc.

Being a chemist, I always have had my suspicions about engine heaters.  But, the literature and glowing stories in the aviation press overshadowed my Thermodynamics 101 class, and I put one on my Mooney.

I had learned in Chemistry 101 that water is a by-product of combustion.  That it remains in the crankcase is evidenced by the appearance of water globules at the top of the dipstick.

My initial hesitation came from my background as a bench chemist doing distillation for a living.  The closed engine was, in fact, a version of a still.  The contents of the engine, oil and water from combustion, were being heated by the electric engine heater, and the water was being distilled off from the oil and was being condensed on the colder parts of the engine--the condenser--and the appearance of globules of water on the top of the dipstick indicated that water was probably condensing on all cooler parts of the engine interior, with no way of escaping the engine because it was a reasonably air-tight system.

Thus came the formula that I learned in Inorganic Chemistry 101.   Iron + Water = Iron Oxide  (Rust).

But, stupidly, I never did anything about it.  I continued to disregard everything I had paid a king's ransom to learn at college.  Worse, I disregarded everything I had learned as a hands-on bench chemist in the real world.

But yesterday, it was all brought into crystalline focus to me when another hands-on bench guy with 30 year's experience told me of his observations gained from opening hundreds, if not thousands of engines.  How could I have been so stupid?

But every engine has water in it after flight.  How do we get rid of it?  Well, I have the solution, but I have to try it out, and then, well, there is the patent application, further testing, and so on.

But mean while, what do we do?  Well, here is my theory.  If the engine guy says that heaters cause corrosion, do nothing.  Use a mild external heater a half hour before departure, and upon landing, open your dipstick cap for an hour after the flight so the engine can distill some of the water vapor out of your engine.  Then put the cap back on.

But the residual water in the oil?  Well, the water is in an emulsified state with the oil.  In freezing weather, it probably stays there to some extent and forms microcrystalline ice crystals that are not terribly reactive with the iron in your engine--but here is the rub--in cold weather, your cylinders cool way down before the hot oil in your sump cools, making the best damn distillation setup possible for  a short period of time.  The hot oil distills hot water vapor into the cold cylinders.  And, if you believe my engine builder friend, it stays in the cam areas and cylinders , and long-term heating at the tops of cylinders by engine heaters causes severe corrosion.

Again, from my chemistry background, if you want to speed up a chemical process, just add heat.  In other words, if you want to make rust faster, raise the temperature of the reactants.

So the bottom line is, in my opinion--water is always present,  and extended heating causes more corrosion than it cures.  Use heating only for a short period of time before and after the flight.

Stay tuned for the responses this thread will bring...

David Jones