On Dec 19, 11:57 am, "Peter R." wrote:
On 12/19/2007 1:51:18 PM, " wrote:

Might ask your neighborhood FBO to use one of their portable heaters
next time around :-)

I have read in several different mags that those portable heaters only warm
the cylinders and not the bottom end (cam shaft) where the heated oil is most
important during the short time most FBOs run the units. Consequently it is
somewhat a waste of time and energy to use that type of heater.

--
Peter

If you heat the cylinders you'll heat the whole engine.
Metal conducts heat.

25°F isn't cold unless you're running heavy oil, like
W100. We run Aeroshell 15W50 year-round and sometimes start these
things at -10°C which is what? around 14°F? And the engines
(Lycomings) all reach TBO. No metal. We put cowl covers on them after
a flight when they're parked outside and start them later on at temps
to -25°C.

The big danger with cold oil is its reluctance to flow.
The oil pump has to suck the oil up from the sump, and cold oil gets
thick. It's like trying to suck a cold, thick milkshake through a
straw; you've all done that. The pump cannot create more than an
absolute vacuum, and if the oil is too thick the pump won't get much
and so the engine won't get it either. The cylinders don't mind
getting little, but the bearings need lots and so does the cam. Idling
too fast will cavitate the pump, delivering no or too little oil.
Idling too slow will throw too little oil on the cams and into the
cylinders. Can get tricky.

More likely damage is burning out starters from long
cranking. Or overpriming and flooding the engine. Or having it run
only briefly and quit, whereupon those cold sparkplugs will frost over
(H2O in the combustion byproducts) and the frost shorts them out. No
more spark. Burn out the starter trying to make it go. Starters have
no cooling system. Starter manufacturers say that a five-minute
cooldown is required after three ten-second cranks.
Kill the battery, and as the acid turns to water as it
discharges, the battery will now freeze (if it's cold enough and the
battery is dead enough and you leave it in the airplane) and split and
spill weakened acid everywhere. It'll still eat your airplane.

Cars typically use 5W30. I used to use 0W30 in my Ford
pickup. Started OK at -35°C. Airplane engines can't use such thin
stuff.

Dan