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Removing the damaged engine.
the oi l cooler, even though the TCM
literature specifies that it be installed on
the top front of the engine.
Oil coolers on this engine model
are attached to the engine at the left rear.
Thi s location is OK for installation of a
probe IF IT IS DO E CORRECTLY. It
was installed incorrectly on my engine.
The male thread on the probe is 114"
diameter. The fema le thread on the oil
cooler is 3/8" diameter.
For installation, a brass reducer
bushing was used, an NPT 3/8" to NPT
1/4". Barry discovered the bushing was
not long enough. He measured the length
of the probe while attached to the bushing
and also the space available in the threaded
hole. The space was not long enough
when using this particular bushing.
The engine is Shipped with a
threaded stud at the bottom of the oil
cooler, adjacent to the internal vernitherm
valve. This valve works much
the same as a coolant thermostat on a
Installing the loaned engine.
car engine. Engines perform best with
warm oil. As the oil warms to optimum
temperature, the valve opens, allowing
oil to flow through the cooler. This cooler
will maintain oi l at a temperature of
about 180' to 200' F, optimally.
When the vernitherm valve opens,
it grows in size due to expansion of a
spring as it heats up. In this particular
installation, the spring was contacting
the probe each time it expanded. This
would have slightly flexed the probe
each time the valve opened and closed,
i.e. one cycle each flight.
The probe broke after only 480
hours of engine running time. When it
broke it allowed the oil, which is under
great pressure, to exit alongside the
probe's wires. The diameter of the probe
tube is about 1/16". In less than six minutes
enough oil was ejected to allow heat
to destroy the engine.
There was not enough oil remaining
in circulation to lubricate the connecting
rod bearings-and probably other things
as weU-by the time it seized. This oil
wou ld have come out in a fine stream
exiting the engine compartment above
the left-side exhaust pipe.
Simply put: The engine failed due
10 heat. The high heat was caused by a
lack of lubrication, resulting in friction.
The loss of lubricating oil was due to a
broken probe. The probe was improperly
installed. The engine did not fail due
to a manufacturing defect.
The threaded stud 01 the bottom of the oil cooler is
adjacent 10 the internal vernitherm valve. The
original oil temperature probe was installed allhis
locolian.
When the original ail lemperature probe was ins lolled, the
installer chose the looation at the boffam of the oil oooler adja·
cent to the vemitherm valve, and installed it incorreclly. The mole
probe thread is 1/4" dia. and the female thread on the oil cooter
is 3/8" die. The brass reducer used was not long enough.
The vemitherm valve works much like a coolant thermostat on a
car engine. As the oil worms to optimum temperature, the valve
opens, allowing oil to flow through the oooler. When the valve
opens, it grows in size due to expansion of a spring as it heats
up. The spring was contacting the oil temperature probe each
time it expanded. stightly flexing the probe each flight. The probe
broke after only 480 hours of engine running time, allowing oil to
escope down the probe tUbe.
ABS April 2008
www.bononza.org Page 10714