There is a stem that is located on the underside of the airplane between the drain valves for the fuel strainer and reservoir tank. It looks like a small stem that is protruding. picture of stem

I have noticed it leaks a small amount of fuel (1 drip per 5 seconds). I am going to talk t my instructor about it but wanted to know what it was called. I am not seeing it in the fuel system diagram.

fuel diagram

Updates: I believe it is a part of the electric auxiliary fuel pump, but want any input.

The aircraft is a Cessna 172R made in 1997.

It is 100LL that is dripping.

Here is the fluid dripping.... Not water. collected 100LL

  • $\begingroup$ A) have you confirmed that it's fuel leaking? (i.e. it smells like fuel) B) You can edit your own post and include your thoughts, instead of adding them as a comment. $\endgroup$
    – FreeMan
    Commented May 2, 2016 at 19:47
  • $\begingroup$ I once noticed it was dripping as we were towing the aircraft during pre-flight, and immediately raised my concern to my instructor. He confirmed it was water, not fuel (it smells and touches different). It rained the night before, so we figured it was just rain water. $\endgroup$
    – kevin
    Commented May 2, 2016 at 21:48
  • $\begingroup$ What C172 variant? I used to fly a C172P, and I don't remember any auxiliary fuel pump or reservoir tank. It did have a low point drain right under the cabin. $\endgroup$ Commented May 3, 2016 at 17:50

1 Answer 1


Ok - got word from the local a&p that this stem is a part of the aux fuel pump. It drains the motor side of the pump of any fuel in case the seal that separates the motor from the pump fails. You wouldn't want fuel getting inside of where the motor has current and sparks, hence this "stem" is the safety backup. The entire pump had to be replaced because overhauling made less sense due to the age of the pump. Turns out it wasn't in the diagrams at all!


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