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How do you check the C172 fuel tank cap vent

Asked by: 4771 views Aircraft Systems, General Aviation

On the C172R/S pre-flight inspection checklist it says to make sure the vent on the fuel tank cap is unobstructed. Where is the vent located on the cap and what does it look like? Also does it serve the same purpose as the long tube-like vent that protrudes from the left wing?

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2 Answers



  1. Josephyr on Mar 01, 2019

    On most C-172 models, there are 3 fuel vents. 1 on each fuel cap, and the little j tube protruding off the left wing, which you mentioned in your question.

    They all serve the same purpose, to prevent suction and a vacuum from building up in the tanks as fuel decreases.

    During pre-flight inspection, you want to ensure that each cap (while you’re checking the fuel amount) has a fuel vent which is completely unobstructed. It looks like a circular, rudder piece attached under the fuel cap. Here is an example of one: https://farm9.staticflickr.com/8723/17314587282_6491335a23.jpg

    If you moved that rubber piece a bit, you’d see a couple small holes underneath. Those are what you are checking for any debris or blockage.

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  2. raj on Mar 05, 2022

    Rudder… rubber… the mention of rudder confused me in the previous answer, but rubber makes a lot more sense as in your last paragraph.

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