The most important thing to heat is the oil, if you can only heat one
thing. I have two heat pads on my oil sump on my 182 and that's it.
Tanis and Reiff work but are only of value if you can't cover the engine
compartment. I have a Kennon cover for mine and the whole engine
compartment is a toasty 80F while the oil is 100F.

wrote:

Dave Butler wrote:
: That's interesting. I've never owned a heater, don't know about Tanis or Reiff,
: since I've been flying, I haven't lived in a climate where heating is called
: for, but...

Generally, the freezing point is about where it's considered a good idea to
preheat. Some people say 40, some 20.

: I'd think "at the head" is not a particularly important place to have the heat.
: Seems to me heating the oil in the crankcase so it can be pumped more quickly
: and start lubricating is a better bang for the buck.

That's important, although with multiweight oils it's less so.

: ... or maybe the rationale is that heating the head relieves the "choke" of the
: cylinder barrel and reduces wear that way? If so, I have to wonder whether the
: few degrees rise you're likely to get from an electric heater has any
: significant effect on the amount of choke.

: Why heat the heads?

: Ignorant and looking to learn... Dave

You got it... there was an article (Mike Busch on avweb?) on the clearance of
the dissimilar metals (pistons and cylinders). There's a point (temperature) where
there is *negative* clearance (i.e. scuffing). If one can warm the thing from 0F to
+40F, you've already gotten past it. Also, the heat loading is uneven due to the
mass. It takes a (relatively) long time for the cylinders and heads to heat up
compared to the lightweight pistons in very close proximity to the fire.

-Cory