Fuel drip

[Guest]

Being a new airplane owner is a brutal learning curve. Just discovered something after shutdown today. One of the 3 breather hoses on the back pilot side of the motor was dripping some fuel. It is the hose attached to a round unit at the rear of the motor. The thing in the back of the picture. Is this normal?

[Guest]

Actually coming from this tube with the blue fitting. 

[Bartman]

That is the sniffle valve and fuel drips from that tube after shutdown are normal. Search for sniffle valve on MooneySpace and you will get lots of info. 

[PT20J]

There are three, sometimes four tubes. The largest is the crankcase breather and it may drip a little oil depending on how much blow by there is and how high you maintain your oil level. There may be a tube for exhaust air from the vacuum pump. There is the drain tube from the sniffle valve which is at the low point of the induction system. After shutdown, heat expands the fuel in the fuel injector lines and pushes some fuel out the injectors into the intake tubes where it collects in the bottom of the intake manifold and drains out the sniffle valve. There shouldn't be a lot of fuel dripping if you leave the mixture control in idle cutoff. If you push the mixture control toward rich after shutdown, you may get quite a bit of fuel draining out the sniffle as the lines all the way back to the fuel pump may drain as residual heat in the engine compartment forces fuel through the servo and out the injectors and down through the sniffle valve. The sniffle valve has a little ball in it that gets sucked closed when the engine is running to prevent air from entering the induction system through the valve which results in a lean mixture. A stuck sniffle valve usually only causes a rough idle since the leak isn't large enough to have much effect at high power.

The forth hose should always be dry. It connects to the engine driven fuel pump and drains any fuel or oil that collects between the two diaphragms in the pump. If this happens, one of the diaphragms is leaking and the pump needs to be replaced. If the second diaphragm cracks, the pump will stop working. There is also a similar drain protruding from the left exhaust cavity behind these engine drain tubes and this is for the aux fuel pump. It also should always be dry or the pump needs to be overhauled.

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[LANCECASPER]

4 hours ago, Kerrville said:

Being a new airplane owner is a brutal learning curve.

Not nearly as brutal as the learning curve for chainsaw juggling. 

[Ragsf15e]

Normal! That was a good, cheap fix!

[RoundTwo]

You have now used up your one complimentary “freebie”. Enjoy the ride.

[Guest]

Thanks y’all.