Foggy Tach

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Kevin
In almost 20 years of GA flying I don’t recall seeing this one before.

I pulled the plane out of my 70 degree hangar and flew an hour in 70 degree weather and noticed condensation developed in my tach gauge.

Anyone seen this? Did it clear up on its own? What would cause that?

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Time for a JPI 930. That’s the only solution
 
I've seen it. It did go away on its own. But it wasn't going from a 70 degree hangar into 70 degree weather.
 
Time for a JPI 930. That’s the only solution
Ha ha...I have both RPM's displayed on my Insight Twin G4.

I've seen it. It did go away on its own. But it wasn't going from a 70 degree hangar into 70 degree weather.
The 70-70 was the strangest part for me. I only climbed up to 6000 or so and it wasn't much cooler up there. I'll get back out there in a couple days and hope it's resolved.
 
The 70-70 was the strangest part for me. I only climbed up to 6000 or so and it wasn't much cooler up there. I'll get back out there in a couple days and hope it's resolved.

The only thing I can think of is that the drop in cabin pressure somehow caused a chamber in the tach to expand, thereby creating an adiabatic drop in temperature. That's reaching a bit, though. I don't think anything in there can expand that much.
 
The only thing I can think of is that the drop in cabin pressure somehow caused a chamber in the tach to expand, thereby creating an adiabatic drop in temperature. That's reaching a bit, though. I don't think anything in there can expand that much.
There is no chamber in a mechanical tach. Most tachs use a spinning magnet that drags an aluminum cup that is attached to the needle. Aluminum isn't magnetic, but the electrical currents generated in the aluminum by the magnet create their own magnetic fields that react with the spinning magnet's field. It's called eddy current effect.

Real old tachs, like the one in my Jodel, were centrifugal devices. Still no chamber.
 
In almost 20 years of GA flying I don’t recall seeing this one before.

I pulled the plane out of my 70 degree hangar and flew an hour in 70 degree weather and noticed condensation developed in my tach gauge.

Anyone seen this? Did it clear up on its own? What would cause that?

View attachment 67174

The seal between the gauge and the gauge glass is degrading/ leaking, so moisture can get inside.

I have a couple of older gauges in the Beech 18 like that.
 
I pulled the plane out of my 70 degree hangar and flew an hour in 70 degree weather and noticed condensation developed in my tach gauge.

Anyone seen this? Did it clear up on its own? What would cause that?
I've seen it before, especially living in a rain forest were humidity is off the scale most of the time. Normally clears when temperature of the gauge rises. As @Fearless Tower says the seal in the gauge is bad.

Not a real expensive fix, but you will need to remove the gauge and send it out for overhaul.
 
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