CAUTION
With the counterweight propeller, the propeller
control must remain at the HIGH PITCH position
during the shut down and left in that position,
so that the oil in the propeller cylinder is returned
tc the engine oil system. If the engine were started
with the propeller control in the INCREASE RPM
position, the immediate demand for oil to change
the propeller pitch might critically decrease that oil
pressure which is available and necessary for
engine lubrication during the start.
RE -DILUTION
When an engine which was previously prepared for cold weather starting
is run up for ground tests, and the oil inlet temperature was above 55°C
(130°F) for more than 15 minutes during the test, it will be necessary to
re-dilute in order to maintain cold weather preparation.
a. Re -Dilute one minute for every 15 minutes of engine test ground run
time, measuring such time from the moment when the oil temperature
has reached 55°C (130°F), or as per Dilution Table, if dilution for a
length of time as found through above calculation would result in a
dilution percentage greater than required.
NOTE
To prevent over-dilution it is advisable in borderline
cases or when in doubt, to stay on the side of under-
dilution.
Example: An engine prepared for cold starting is run up for ground tests
for a total of 70 minutes, during which period the engine oil temperature
was above 55°C (130° F) for 55 minutes. Anticipated Ambient Outside
Temperature: -Z0°C (-5°F).
Re-Dilution Time: 55:15 = 3 2/3 minutes. In accordance with the above
NOTE the suggested re-dilution time would then be 3 minutes. However,
since only a 15% oil dilution is required for an anticipated temperature
of -20C the re-dilution process is stopped after 2 minutes, as per Oil
Dilution Table.

NOTE
In extreme cold weather only a negligible amount
of fuel is boiled-off during a short ground run.
Under these conditions there is no need for re-dilution
of the engine oil.
CAUTION
When re-diluting after engine has been operated for
less than 2 hours of combined boil-off ground run
and flying time, the residual gasoline (2-4%) remaining
in the engine oil should be taken into account and
caution should be used.
DILUTION BOIL-OFF
Oil dilution is used for the purpose of facilitating engine starting at low
ambient temperatures.
The diluted engine oil with its low viscosity is, therefore, not suitable for
flying with normal operating oil temperatures of 60-75°C. Thus, prior to
take -off most of the added gasoline must be boiled-off after a cold start.
This is done by running the engine at about 1200 to 1500 rpm with the oil
temperature above 55°C for a period of 15 minutes for each minute of the
preceding oil dilution run.
Since the boil-off does not begin until the oil temperature has reached 55°C
boil-off times calculated on the basis of 15 minutes for 1 minute of the dilution
run are measured from this point.
NOTE
Should the oil pressure at any time during
the boil-off ground run, drop below 45 psi
the engine is to be shut down to cool before
continuing.

DILUTION TIMES AND PERCENTAGES
   Times for dilution percentages are as follows:

Oil Temperature for Dilution:                         Based on Oil
30'C - 50'C  (85'F - 125'F)                           Grade No. 1100

Aticipated Ambient                                Dilution %     Dilution Time
Outside Temperature                            Recommended    in minutes
                                                                                  at 1200 RPM

1  above +5'C  (40'F)                               -                        -
2  +5'C to -10'C   (15'F)                           8%                     1
3  -10'C to -20'C  (-5'F)                           15%                    2
4  -20'C to -30'C  (-25'F)                         22%                    3
5  -30'C to -40'C  (-40'F)                         30%                    4
6  -40'C to  -50'C  (-60'F)                        35%                    5

Note:
The above table is based on the use of grade 1100 oil.  To convert the table for the use of thinner Grade 1080 oil, Increase the expected ambient outside temperature by 5'C (9'F) to obtain equivalent conditions in the table.

Example:  Using Grade 1100 Oil
If an ambient outside temperature at the time of the next engine start of -23'C  (-10'F) is anticipated, dilution percentage, times etc. apply as in row 4 of table.

Using Grade 1080 Oil
If the same ambient outside temperature of -23°C (-10°F) is anticipated,
5°C (9°F) to this temperature as follows: -23+ 5 — -18°C. Dilute the ti
ner Grade 1080 oil for a corrected outside temperature of -18°C (0°F)
following row 3 of the Oil Dilution Table.

Oil Dilution Procedures and Theory was a must for all Military Pilots and  Flying Engineers and was on the Civilian Air Transport Rating Exam.  A good Civilian Chief Pilot made sure his line Captains and Co-Pilots new the proper procedure and theory for the aeroplane they flew.  Oil Dilution was not the resposibilty of the Flight Engineer if you had one, most civilian operators did not carry Flight Engineers on DC3s.

Hope this gives a rough idea what Oil Dilution is all about on the DHC-3 "Otter".

Cheers...Happy Landings...Doug

Good morning Brett...

Did you ever use a Herman Nelson Heater...wonderful units.

With the Douglas DC3s & 4s along with the DeHavilland DHC-3 Otters we had wing and engine covers.
Covers for most control surfaces along with control locks.

Well when we were using the Herman Nelson on the engines we could also use it to pre-warm the inside as well...the system worked well.

The one thing I found was the Northern Cold was not damp or bone chilling like here in Southern Ontario. Lots of times I only had on a good vest but here in Southern Ontario one needs a bloody snowmobile suite to keep the cold out.

Have you seen the new little portable propane heaters yet?  I almost purchased one but with the hangar it would have been a waste of money. 

I do remember one winter we had to take the battery out and drain the oil in the aircraft and put both beside the wood stove as we had no APU.  Don't miss those days.  Well maybe I do because someone always had a good bottle of wobbly pop to pass around to keep you warm.   

Cheers...Happy Landings...Doug