Engine pre-heaters

Here's a question for all you cold climate folks (and Mahlon).

I have an IO-360-A3B6D, but the question applies to any traditional engine type. What are the issues with using sump type engine pre-heaters all of the time. What I mean is, are there any problems with just leaving the heater plugged in all of the time during the winter, such that I can fly at a moments notice.

I have one of the sump heaters that Van's sells with the thermostat on it, so it should never overheat. In addition, my electricity is included in my rent, so I'm not worried about that. What concerns me are any problems that might crop up with respect to corrosion inside the engine.

I have a friend who is an AME (Canadian version of an A & P) with an RV-6A and he just leaves his heater plugged in all winter, and he hasn't had any problems.

Thoughts, anyone ?

Thanks

Mark,

Let me start out by saying I am not an A&P. I'm just some guy who flys airplanes and is building an RV-9. However, I did grow up in Northern Michigan and what we used to do was use a dipstick heater on our 150 and left it plugged in all the time.

If you are worried about leaving it on for other reasons, you can buy a RS Beeper Box so you can call your pre-heater and tell it to turn on. Or, you can make one, like this guy did.

This has been debated ad nauseum and beyond on the CPA forums...
My personal opinion is that plugging it in and leaving it is not harmful IF you have the whole engine heated (i.e. not just the bottom which could heat the moisture out of the oil and cause it to condense on the top end). Having said that, even if you have just an oil pan heater and cover the cowl with a blanket after several hours the engine compartment will equilibrate.
I think the bad thing is thermal cycling - turning it on and off without running the engine to boil off condensation. I leave my Reiff system on the IO-360 in my 172 plugged in all the time (in the winter), fly once a week or more, and don't worry about it otherwise.
There are some that will say this is bad, but it seems to me that when I fly in the summer, park the plane, and the temps stay in the 90's (plus high IN humidity) what is the difference to plugging the engine in in the winter and keeping the temps 90-100F with comparatively dry air?

Thomas
-8 wings

The purists will tell you yes, it hurts the engine because it causes condensation to form on the upper internal parts of the engine. I think it's less of a problem if you fly frequently (more than once a week).