Gauge indication, or real issue?


Pre-takeoff checklist
May 12, 2009
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Digital oil pressure gauge started to go down and up, it never went below green.
Could it be indication of some engine trouble or just instrument glitch?
I also have an analogue gauge and that one did not move at all.

Analog gauges are typically slow to react and just average out readings to the point that you can (in a car) lose all oil pressure for a second or two and never notice.
Personally I wouldn't get excited about it bouncing between 38 and 47, but that's an opinion from some random guy who is not an A&P.
I'd check the OP sensor ...
Poor engine grounding can do that. The alternator's charging current runs through the engine, and any resistance between the engine and airframe can cause that current to find other paths. Through the temp sensor to the instrument is one of them, and since a digital gauge uses far less current than the old analog, it's more sensitive to such flows.

One other thing: where is the new sensor located?
A year ago I had a digital fuel pressure gauge start to pulse on me. Turns out for digital fuel senders you need to have an air pocket in the line to even out the pulses from a mechanical pump. Another time I had another digital gauge that was Erratic and it turned out to be a broken wire that was making intermittent contact. I feel that wiring and senders and gauges are more prone to failure than oil pumps are. FWIW, my digital oil, pressure gauge does not fluctuate by much.
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Well that gauge saved me 4 years ago after the engine was just overhauled, I took off, third flight and at 1,000ft the oil pressure started to drop, I turned around head back to the airport psi continued to drop, it showed zero when I touched down.
We had to open the engine, there was no damage, the cause was the Oil pump, it had a piece of safety wire from when it was overhauled and was bypassing the oil.
FWIW department: The older technology sending units used in the auto industry (basically a potentiometer) can react poorly to engine vibration and cause intermittent readings. That's why the oil pressure gauge in your car isn't really a gauge anymore (and I know the guy to "blame" for this). I don't have a clue about what technology is used with your sending unit - but that would be another possibility.