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What is this drain tube?


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Today after a short taxis to get fuel I noticed one of these drain tubes dripping a few drops of fuel.  I started looking for this because I could smell fuel In the cockpit.

what are these drains for?  What type of dripping is normal?

 

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Game: Name that drain...

1) is that the engine block vent?  Oil...

2) is that the sniffle valve drain? Dark Blue fuel... dark from evaporation

3) is that the fuel pump drain? Light blue fuel

4) is that the electric fuel pump drain? Light blue fuel.

5) battery boxes get vents too.  Use caution taking samples, could be battery acid if things aren't going well with the battery...

What is coming out of it?

These are what comes to mind.  Looking to see what it is connected to probably answers the question.  Good to double check since it is a hose and may have been moved compared to when the plane was new...

 

PP thoughts, not a mechanic...

Best regards,

-a-

Edited by carusoam
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Putting two and two together...

read up on the sniffle valve.  It has something to do with excess fuel draining out of the FI system.  It is possible that some dripping in this case is normal.  There is a plastic ball that blocks the drain keeping air from being drawn in...

PP thoughts only, I have forgotten the details of the sniffle valve, but I know there is plenty shared on MS...

Best regards,

-a-

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Hello Philip,

Welcome to Mooney Space.  The vents in your picture are from the sniffle valve which drains raw fuel from the induction system, leakage from here is normal.  The valve opens when the engine is not running and closes when it is.

The other is from the engine driven fuel pump, leakage from here would indicated a fuel pump diaphragm failure.

Others in the same area are a larger aluminum tube which is the crankcase breather, it will drip water.  Just behind the left cowl flap is the fuel gascolator drain and the electric fuel pump vent, neither of these should drip or leak.

Clarence

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Thanks for the information.  I have not removed the cowling to trace them out but I see on goes toward the throttle body and one goes up the firewall (I guess that's the fuel pump drain).  I'll pay close attention next time I run it to see which is leaking.

Thanks again.

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My sniffle does drip a bit, but 1) the tubing does not look quite like this, it originates from the lower case, where the intake is, and 2) it does not happen at every shutdown, sometimes only. M20E IO-320-A1A here.

Edited by zaitcev
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4 hours ago, zaitcev said:

My sniffle does drip a bit, but 1) the tubing does not look quite like this, it originates from the lower case, where the intake is, and 2) it does not happen at every shutdown, sometimes only. M20E IO-320-A1A here.

It must be dripping because you have the wrong engine in your plane!  It should be an IO360-A1A.

Clarence

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