avgas sight glass deviation

[teeweed]

Can somebody tell me why my sight glass will read as if there is no fuel...while I am parked in the hanger? Once I start to roll it comes up a little so I can see the fuel.. Then by the time I have done my run up it shows more volume. Then flying the fuel sight glass says about 1/4 to 1/2. Could I have some kind of airlock. Strange it does this in both tanks. Thanks Mark

 

[Speedo]

What happens if you remove the tank caps while you're parked in the hangar? Does the fuel rise in the sight glass?

 

[RON NORMARK]

The sight gages on my Cub were slow to react when filling the tank. I thought it was because of blockage in the bottom tank tube. To my surprise, the blockage was in the top tank tube, which trapped air in the glass sight tube.

Ron

 

[teeweed]

I will check to see what happens when I remove the fuel cap. One of my sight glass is missing the ball. I wonder if it's stuck somewhere, crumbled up and causing this. Thanks Mark

 

[tamarack]

I have seen the (older) little black seals in the sight gauge glass swell up and cause blockages, thus indicating fuel in an empty tank. The cork ones don't seem to swell up.

However, looking at my stock of sight glass seals (all cork) I can see that the hole size is not really consistent. I suppose with a too small hole they could also cause blockage.

Vickie

 

[SuperCub MD]

Watch the gauges when you are taxiing across rough ground or flying in rough air. Your balls should be bouncing around a lot. If they are not, you have a partial blockage in the gauges. The most common cause is a rubber gasket swollen up from car gas. The cork gaskets don't swell.

 

[kase]

The bottom elbow in the site gage is suppose to have some blockage. Solder the end shut and then drill a .070 hole in it. That I assume is so the balls dont bounce around to much in the gage? Drawing 10834.

 

[SuperCub MD]

I always figured the restriction was to slow down the bounce. But when your balls stop bouncing completely, you got problems.

 

[Yard Dart]

They could just be cold.

 

[RON NORMARK]

I think the restriction in the bottom sight gauge fitting is there to prevent a catastrophic leak if the gauge breaks. It is the same reason there is a restriction in the oil pressure gauge line.

Ron

 

[PA-18]

I much prefer "Tighty Whitey's"to boxers,it solved my problem!
Damn I thought this was that other website.