Friday, July 17, 2015

Exhaust Gas Temperature

Flying might not be all plain sailing,
but the fun of it is worth the price. 
~ Amelia Earhart ~

Ceiling and visibility unlimited. Finally, a good weather day. Two training flights scheduled and the weather would be perfect. The briefing and preflight went well. The engine run-up was normal and the static ground check just before take-off had the shaft spinning just over 4900RPM. Winds were light and out of the east. We departed to the south heading toward Pottstown Muni (N47) for some landing practice.

As I prepared the student for his entry procedures I noticed the left EGT* was high. Oil pressure & temperature normal, CHT normal, no abnormal noise or shuttering, just an occasional yellow blip on the instrument.  I elected to proceed. 

As we descended it cooled off but leveling at pattern altitude it started to rise again. We did a low pass and departed to fly north up the Lehigh Valley. Level flight, power at about 5000RPM the temperature started to rise again. Time to go home.

I added maximum power and raised the nose. The temperature dropped. Leveled off in cruise, it rose. Descended at at idle power it dropped. No other indications.

I did an uneventful straight in approach at Quakertown. With the engine running at idle on the ramp we had no abnormal indications.  I was stumped.

Until I turned the key to shut her down. Only two clicks, not three.

When the student had performed the magneto check during the engine run-up he had returned the switch to the Left, not Both position.

I should have thought of that. 

*An exhaust gas temperature gauge (EGT gauge) is a meter used to monitor the exhaust gas temperature of an internal combustion engine in conjunction with a thermocouple-type pyrometer. EGT is an indication of how hot the combustion process is in the cylinders, and the amount of "afterburning" that is occurring in the exhaust manifold. EGT is also directly related to the air/fuel ratio. The excess fuel will act as a coolant. The richer the air/fuel ratio, the higher lower the EGT will be. Reference:

1 comment:

  1. Helpful info about EGT. Thanks.
    I've got an ongoing issue with randomly high EGT, so I read with interest. At the end, you wrote "The richer the air/fuel ratio, the higher the EGT will be." I think of richer as being higher ratio of fuel to air, which lowers EGT - is that right?