On Feb 2, 4:14 pm, "nrp" wrote:
On Feb 2, 3:52 pm, wrote:

We've started our airplanes at ambient temps as low as -25C (-13F)
without preheat, but they sure don't like it.

I'm surprised you got by with that. Must have been a Continental
engine?

Six Lycomings.

Lycomings have no crankshaft feature that will sling oil to
the camshaft lobes & most oil pump output has to flow over the relief
valve which has no access to the heat of the engine. It would be
interesting to find out how long it takes a genuine oil fog to
develop, My guess is quite a while.

Aeroshell 15W50 has the Lycoming-recommended additive to protect
the cam during dry starts. It has served us well.
The cam gets enough splash off the crank once the engine's running.
It's coming off the sides of the main and rod bearings.

Another factor is how long an engine has been sitting. A couple of
days is one thing, but if it has been two weeks a few more drops of
camshaft oil would have drained such that the need for preheat has to
be greater.

We hangar the airplanes every night at 5C. They start just fine at
those temps, six days a week. It's when they sit out at -25C for a few
hours that we have to get really careful, or for a weekend. They will
need preheat if they don't fire and stay running really early in the
attempt. With the frost and ice and snow around here they often need
hangaring anyhow.

We get the full 2000 hours out of them and could go another
500, easily. The compressions are in the mid-to-high 70s when they
come off, and there's no metal in the filters. The secret, I suppose,
is to run them frequently, and not for short 20-minute flights. And
use the Aeroshell with the additive. We had some cam problems before
switching to it. It costs more, but it costs less. Get the idea?

Dan