Good evening all....

Had a couple of inquiries about this so here it is for the DHC-3 "Otter".

OIL DILUTION
GENERAL
At an engine speed of 1200 rpm, the engine oil in circulation makes one
complete pass through the system in each minute. Therefore, complete dilu
tion can be accomplished only if carried out in multiples of one minute. For
recommended dilution percentages and times at various outside ambient
temperatures, see Dilution Table, paragraph 6.3.9.
OIL TEMPERATURE
For the beginning and duration of the dilution run, the oil inlet temperature
should be between 30°C (85°F) and 50°C (125°F). Dilution at higher oil
inlet temperatures leads to early loss of safe oil pressure and will not perm
it recommended dilution percentages to be reached. Owing to the slow
flow of engine oil through the system, dilution at lower oil temperatures
causes over-dilution and must be avoided.
OIL PRESSURE
During the dilution run, the oil pressure should be closely watched. While
it is safe to dilute the engine oil in circulation at inlet temperatures anyw
here between 30 and 50°C, (85-125°F), the oil pressure should never drop
below the minimum idling pressure of 10 psi. The constantly decreasing
viscosity of the oil in circulation may cause the oil pressure to drop to this
latter value during the dilution run.
This decrease is a means of ascertaining that the dilution valve is operati
ng properly and there is no cause for alarm provided pressure does not
fall below 10 psi.

To ensure that the oil pressure does not fall off to critical values during a
long dilution run, the oil inlet temperature at the beginning of an extended
dilution run must be as close to 30°C (85°F) as possible.
Inadvertent dilution caused through a faulty solenoid or a leaking fuel valve
will produce low oil pressures and excessive breather pipe losses and must
be watched for.
OIL TANK LEVEL
When the solenoid opens the dilution valve, the #43 nozzle on the valve
assembly meters the flow of fuel to approximately 1/4 Imp. gallon per
minute, i.e. adds one Imperial gallon of fuel to the engine oil in a four
minute dilution run.
CAUTION
Since the oil tank has a capacity of 9 Imp. gallons,
it should never be filled to more than 7 3/4 to 8
Imp. gallons to provide the necessary space for the
diluent.
The addition of fuel may cause the fluid level in the tank to rise slightly
above the filler inlet level and the filler cap should not be removed if the
engine oil has been diluted. Oil level in tank will return to normal after
boil-off.
OIL SCREEN INSPECTION
Gasoline used to dilute the oil tends to loosen carbon and sludge deposits.
The oil screen should, therefore, be cleaned immediately after the first
use of the dilution system, and is to be inspected daily until carbon coll
ection on the screen returns to normal. Then the usual screen inspection
will be adequate.
After the change-over to oil dilution, the oil pressure may indicate the
occurence of oil screen clogging and should, therefore, be watched
closely.
NOTE
Oil dilution should not be used intermittently during
the season, but continued once it has been started.
Otherwise, cleaning of the screen must be repeated
EACH time.

s-s. .
DILUTION PROCEDURE
To dilute engine oil in circulation proceed as follows:
a. Allow oil temperature to drop to between 30°C and 50°C (85° F to
125°F) during shut-down run of the engine.
NOTE
If oil temperature cannot be reduced sufficiently,
shut engine off until oil has cooled down to
approximately 40°C (105°F).
b. Make sure oil level in tank is at 6 (max. 8) gallons mark. If necessary,
stop engine and have oil drained or added, as required.
c. For anticipated temperature at next engine start, select dilution perc
entage required from the Dilution Table.
d. Booster pump ON.
e. Propeller control to fully INCREASE RPM.
f. Throttle to give 1200 rpm.
g. Dilution switch held to ON position for the recommended dilution time in
full minutes.
NOTE
Maintain oil temperature below 50°C and pressure
above 10 psi during dilution run. If oil temperature
should rise above 50°C, shut engine down, allow oil
to cool, restart and dilute for remainder of dilution
time
h. During the last 20 seconds of dilution run, move propeller control
several times over its full range to circulate diluted oil through the
propeller pitch changing system.
j. After the oil dilution time has elapsed, stop the engine with the prop
eller control positioned as follows:
1. Counterweight propeller - HIGH PITCH.
2. Hydromatic propeller - Full INCREASE RPM.
Mixture control - IDLE CUT - OFF.
NOTE
Hold oil dilution switch at the OIL
DIL position until the engine stops.
1. Fuel selector and booster pump switch - OFF.