MGL Avionics Stratomaster Ultra “L” Owner’s manual
Page 71
results in very accurate measurements providing you install high quality probes. Here are some
guidelines:
EGT Probes: select probes that are made from 316 stainless steel and that use glass-fiber
insulated conductors. Teflon insulated conductors as found in many cheap probes introduce
errors as the insulation melts moving the measuring point towards the mounting bolt which
transfers a lot of heat to the exhaust material. This results in under reading probes. Stay away
from probes that use simple plastic heat shrink sleeving – it does not last. Choose probes that
use a generous amount of stainless steel spring as strain relief. The Bolt itself should be stainless
as well or it will rust very quickly.
CHT probes: These are made from washers to fit spark-plug bases. Temperatures are
considerably lower so most thermocouple cables will work without problems. The biggest area of
concern should be the connection of the thermocouple cable to the washer. This often breaks
after the spark plug has been changed a few times. Choose a probe that is suitably reinforced at
this point for a long and trouble free life.
EGT and CHT probes supplied by MGL Avionics are of highest quality. We recommend that you
consider using our probes if at all possible.
Warning:
Four stroke engines produce much hotter exhaust gases compared to two stroke
engines. Do not use EGT probes made from lower grade stainless steel (for example 310), these
probes will not withstand the high temperatures and can fail as the metal gets very soft at 800
degrees C. Many four strokes (such as the Rotax 912) will produce exhaust gases of up to 850
degrees C.
Important installation note:
EGT and CHT probes use wire made from plain Iron and other basic metals. As a result these
probes are not able to withstand much flexing of the wires due to engine vibrations. Avoid making
nice looking coils or similar constructions that will result in excessive vibration or flexing of the
wire. Route the cables from the probe points tightly along suitable engine mounting points
eliminating any chance of unnecessary wire flexing during engine operation.
