Cold Weather PreHeating

On 1/31/2007 3:31:14 PM, "pgbnh" wrote:

But anyway, what's the common wisdom on preheating.

I park my aircraft in an unheated t-hangar in central NY state. Normally, I
plug the Tanis heater in when temps get around 40 degrees and I will further
wrap the cowling and cover the prop with an insulated cover when temps are
forecasted to drop below 25 degrees F or so. Keep in mind, though, that this
is a newly overhauled engine and I am simply preserving my investment.

One morning a couple of months ago I arrived at my t-hangar to discover that
the plug had somehow pulled out of the socket the previous evening and the
engine was at ambient temperature, somewhere around 36 degrees F.

I did not have the time to wait the three hours for the Tanis heater to warm
the block, so I called my mechanic and asked him if it would hurt the engine
to start at that temperature. This mechanic has 40-years in the business, so
I trusted him when he told me that there would be no harm in starting above
freezing. Being that my engine is a turbonormalized 6 cylinder, it was more
important for me to wait until the oil temperature hit 120 degrees before
applying full power. 36 degrees to 120 is a lot of idling.

Anyway, when I asked him what temperature would be a concern, he opined that
when temperatures dip into the upper 20s or lower, preheating becomes
important to engine health.

Then again, I have seen flight school aircraft started without preheat when
temps were around 0 degrees F, but I have also heard of these same engines
having stuck valves and other complications, so I wouldn't use that as a
guideline.

--
Peter

Now that winter has finally arrived in the Northeast, it is time to enjoy
the benefits of cold, dense air. wow - I wish I could see those climb rates
in August.

But anyway, what's the common wisdom on preheating. Granted, in an ideal
world, preheating is probably a good idea anytime it's below 40, but it IS a
pain for those of us who are forced to tie down outside and have no access
to electricity. At what temperature point are you comfortable starting
WITHOUT a preheat? (If it matters, this is for a Lyc IO360 that will start
easily down to about 10 deg).

Any mechanics care to comment on what they have seen happen to engines which
have routinely been started cold?

In article , "pgbnh"
wrote:

But anyway, what's the common wisdom on preheating. Granted, in an ideal
world, preheating is probably a good idea anytime it's below 40, but it IS a
pain for those of us who are forced to tie down outside and have no access
to electricity. At what temperature point are you comfortable starting
WITHOUT a preheat? (If it matters, this is for a Lyc IO360 that will start
easily down to about 10 deg).

I use a red dragon preheater. Since I own it I simply take the time
and accept the hassle of preheating anytime below 40 degrees. My
cherokee 140 starts a lot easier.

Doing the preheat was a lot easier when I had a T-hangar, but I still
preheat even though I'm on a crappy tie-down.

--
Bob Noel
Looking for a sig the
lawyers will hate

I believe that Lycoming recommends preheat below 20 degrees to prevent
engine damage..

If you are in even an unheated hangar, the OAT and the engine temperature
can be significantly different. On one of our colder days in Tucson when
the air outside the hangar was 30, a thermometer showed the head fin
temperature to be 45. Of course an aircraft parked outside would have been
a different story.

--
Best Regards,
Mike

http://photoshow.comcast.net/mikenoel

I'm a uniter, not a divider. - GWB, 1999.

"pgbnh" wrote in message
...
Now that winter has finally arrived in the Northeast, it is time to enjoy
the benefits of cold, dense air. wow - I wish I could see those climb
rates in August.

But anyway, what's the common wisdom on preheating. Granted, in an ideal
world, preheating is probably a good idea anytime it's below 40, but it IS
a pain for those of us who are forced to tie down outside and have no
access to electricity. At what temperature point are you comfortable
starting WITHOUT a preheat? (If it matters, this is for a Lyc IO360 that
will start easily down to about 10 deg).

Any mechanics care to comment on what they have seen happen to engines
which have routinely been started cold?

Depends on the oil you're using, for one thing. If multi-viscosity, I
wouldn't worry about anything down to 20 or so. Lycoming's web site
says 10F is OK, but my IO360 turns over pretty slowly below 20 - that
might be from a cold battery, though.

I think that a good approach if you live where it's really cold for an
extended period is to have both crankcase pad and electric cylinder
heater. Plug both into one of those cube taps that turns on when the
temp gets below 35F and just leave it on. Moisture does not form if
the engine is evenly heated, so wrapping the cowl is helpful, as is
wrapping the prop and spinner.

pgbnh wrote:
Now that winter has finally arrived in the Northeast, it is time to enjoy
the benefits of cold, dense air. wow - I wish I could see those climb rates
in August.

But anyway, what's the common wisdom on preheating. Granted, in an ideal
world, preheating is probably a good idea anytime it's below 40, but it IS a
pain for those of us who are forced to tie down outside and have no access
to electricity. At what temperature point are you comfortable starting
WITHOUT a preheat? (If it matters, this is for a Lyc IO360 that will start
easily down to about 10 deg).

Any mechanics care to comment on what they have seen happen to engines which
have routinely been started cold?



I plug in my preheater when the temperature is less that 40F. It has
about 300 hours on since factory OH. I put a blanket on the cowl and
seal the front openings. I also put a drop light on the rudder pedals to
let the warm air heat the gyros. My plane is in an unheated hangar.

--

Regards, Ross
C-172F 180HP
KSWI

We've started our airplanes at ambient temps as low as -25C (-13F)
without preheat, but they sure don't like it. We run Aeroshell 15W50,
and it gets thick at that temperature. The battery loses most of its
cranking power in those conditions.
Big dangers:
1. Cranking too long, overheating the starter, maybe burning it out.
Just replaced one like that. $460. Give up and go home.
2. Priming too much and too long before cranking. The fuel mists into
the intake manifold, but will coalesce onto the manifold walls and run
out into the airbox, creating a fire hazard. Priming too much will
result in a brief run and stop, frosting those cold sparkplugs and
shorting them. Whatever the order of checklist, the prime should
happen immediately before start, not three or four items earlier.
Remember that the vapor pressure of the fuel is really low when it's
cold and won't fire consistently at all. Adding more via the primer
doesn't help, it just increases the flooding problem.
3. Too low or too high revs after start. Too low and the oil won't get
thrown off the crank into the cylinders. Too high and the pump will
cavitate, being unable to suck that thick oil up from the case. Think
McDonalds milkshake. 500-700 RPM works for us. I wouldn't even think
of starting an engine at those temps if it had W100 in it.
4. Idle it for a long time to get the cylinders warmed up and the oil
viscosity down. Taking off on a cold engine is false economy and will
soon enough get you, either financially or fatally.

Dan

According to Lycoming, an even bigger danger is that, at -10 deg. F,
engine tolerances are such that there may be zero, none, nada clearance
between important surfaces, like the crankshaft and it's bearings. The
aluminum case shrinks more than the steel crank, and one start under
those conditions will, not might but will, destroy the engine.

Rip

wrote:
We've started our airplanes at ambient temps as low as -25C (-13F)
without preheat, but they sure don't like it. We run Aeroshell 15W50,
and it gets thick at that temperature. The battery loses most of its
cranking power in those conditions.
Big dangers:
1. Cranking too long, overheating the starter, maybe burning it out.
Just replaced one like that. $460. Give up and go home.
2. Priming too much and too long before cranking. The fuel mists into
the intake manifold, but will coalesce onto the manifold walls and run
out into the airbox, creating a fire hazard. Priming too much will
result in a brief run and stop, frosting those cold sparkplugs and
shorting them. Whatever the order of checklist, the prime should
happen immediately before start, not three or four items earlier.
Remember that the vapor pressure of the fuel is really low when it's
cold and won't fire consistently at all. Adding more via the primer
doesn't help, it just increases the flooding problem.
3. Too low or too high revs after start. Too low and the oil won't get
thrown off the crank into the cylinders. Too high and the pump will
cavitate, being unable to suck that thick oil up from the case. Think
McDonalds milkshake. 500-700 RPM works for us. I wouldn't even think
of starting an engine at those temps if it had W100 in it.
4. Idle it for a long time to get the cylinders warmed up and the oil
viscosity down. Taking off on a cold engine is false economy and will
soon enough get you, either financially or fatally.

Dan

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? 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.

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.

Having summer 50 weight (100W) oil instead of winter (say SAE 20
weight) is about the same as a 40 degF temperature penalty.

That's my take on it.