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Low Oil and Instruments?


iaw4

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hi roger----I believe you that oil does not evaporate.  If it does not show under the airplane, it's likely mostly still in the engine.  :-).

will a functioning dynon d120  (oil pressure or temperature) give me good hints/advice when I need to pour more oil into the engine?

 

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IAW,

I agree with Tom.

Oil pressure is not a good indicator of oil quantity. It's a binary indicator. If there's any oil at the pickup then you'll see full pressure the oil pump outlet. If there's not oil at the pickup, then the oil pressure will be zero. In which case, you'll need to shut the engine down quickly to prevent it from seizing.

There might be some period of time when the pump would be dry and the gauge reading zero until another few drops of oil blow out of the engine, thorough the reservoir and into the pump, at which time the pump would again read full pressure momentarily, before dropping back to zero. So you might say that a indicator bouncing between full pressure and zero pressure is possibly an indication of low oil level. But it's still too late to save the engine.

Oil temperature would be no more useful in measuring oil quantity. There are at least four major paths for heat to flow out of our engines. The biggest is surely out the exhaust. Second is probably the heat lost to forced convection in the engine compartment. The third is probably the heat carried from the water at the radiator and the fourth is probably the heat carried from the oil at the oil cooler. All the paths are interrelated in that all provide some degree of oil cooling.

Among the heat lost to forced convection in the engine compartment is the heat from the oil reservoir, and it is a function of the amount of oil in the reservoir. However, this heat flow is a small percent of the total. And there are so many variables: outside air temperature, pressure altitude, air speed, angle of attack, throttle setting, mixture, combustion efficiency, timing, etc. It would be very difficult to detect the difference in oil temperature due to reduced oil quantity. At least up to the point where the oil is no longer moving, at which point, again, it's too late anyway.

Mike Koerner

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