Fuel residue on shutdown

[William Hughes]

I recently had a very long (6.4 hours in the air) flight in two legs from Vancouver to Saskatoon. The end of the flight into CYXE was a bright hot sunny day and descended on low power from 9,500 feet to 2,700 feet, and then slowed down even more to allow three medivac departures and a couple of jet arrivals ahead of me. About 15 minutes all told with the MP below 15". And then due to the wind it was about a two mile taxi to get to the aerocentre. Its a full service place and there was a rampie with wheel-chocks waiting for me to shutdown.

Once I had, he knocked on the storm window, and said, "Hey, there is something leaking out of your plane." I told him that it was 55 years old and there is always something leaking out. In all seriousness though, it was new to me. About two or three teaspoons of thick blue residue, rather like oil, and smells like fuel, slopped out of the cowl at the front gear well, and dripped onto the forks and a bit on the tire. Photos below.

I've seen staining like this on the aluminum structure before but it was always slight. I reproduced the effect the next day on an approach into Nipawin and called ahead to get a person to witness the shutdown, and the same thing happened. Just as the engine gasps its last a few spurts of the blue stuff slops out onto the wheel.

I crawled around underneath and absolutely cannot see where this is coming from. There is no sign of it on the engine sump, or rods, or cylinders, or on the inside of the lower cowl. There is a little bit clinging to the underside of the cowl along the edge of the wheel well, and it drips down right at the wheel where the opening gets larger.

Any ideas?

[Timothy Poole]

Hi William -- FYI your images are not displaying properly.

[William Hughes]

Thanks - fixed images.

[Timothy Poole]

What engine is in your aircraft? If it's fuel injected, any chance the sniffle valve on the bottom of the sump has failed?

[Charles Schefer]

Perhaps a mix of blow-by engine oil along with fuel? On the Cirrus (newer plane) I've sometimes seen this sort of thing. If there is excessive priming, the extra fuel vents out and inevitable blow by oil comes out in a similar spot. With heat from the engine the whole mess gets viscous and sticky. Just a guess.

- Charles

[William Hughes]

Naturally aspirated 250. Mentioning excessive prime is interesting. A few months ago I started keeping careful notes at each flight on how to get the most reliable and smooth start. I ended up with three pumps of the throttle, six prime, and the throttle cracked open, for a smooth fast start up. I was thinking that six strokes was way *way* too much primer, however.

If I think of fuel related things that I have changed recently, perhaps that is it. I'll go back to a two or three stroke prime and see if the residue stops.

[Timothy Poole]

Three pumps of the throttle is your accelerator pump squirting raw fuel into the carb, which is just going to run down into the carb box. You are significantly increasing your risks of an intake fire using this method.

Have you cleaned the primer nozzles recently? Six priming squirts on top of 3 throttle pumps shouldn't be necessary for your engine to start.

Tim

[William Hughes]

It was a straight up fuel leak at the fitting that joins the output from the engine driven pump to the output of the electric driven pump. The problem was getting worse, and then there started to be quite a discrepancy between the fuel receipts and the totalizer output. The fuel totalizer was downstream after the leaking fitting. I was thinking that the totalizer matched what I expected from the performance, and that I was doing an inconsistent job of filling the tanks.

Not so. A stream of gasoline was shooting onto the exhaust shroud back there. It was evaporating (and perhaps burning a bit) in the windstorm during flight, and the residue would drip out the bottom on shutdown.

Why no one thought to just turn on the electric fuel pump on the ground and have a look far far earlier is a completely different question...

Anyways, it's fixed now, and no one died in a fire, and my last flight to Edmonton and back (6.5 hours) cost way way less money and the engine compartment was much cleaner and smelled way way nicer.

So that is all good.

[Timothy Poole]

Glad you were able to figure it out. Sounds like you averted a potentially nasty outcome farther down the road.

Tim

[Clarence Beintema]

Turning on, listening to and watching the fuel pressure prior to starting should be standard practice and part of the pre fight. One of the poor parts of the 250 is both boost pumps are on the same switch making it hard to distinguish that they are both working.

Clarence

[William Hughes]

That is my standard practice - but I have to confess that I didn't have a benchmark for what "normal" looked like. The leak was only evident once the cowl was off and the engine off and the electric pumps on and you got close and had a good look - it was easier to hear than see. It didn't show up as "low" pressure or a "slow rise" inside the cockpit. I can say that the fuel pressure needle seems less "jumpy" now, both on the ground before startup, and in the air during flight. Although that is also a subjective opinion...

[Gene Ridder]

After reading your post I turned on the electric fuel pumps for preflight. Low and behold a substantial fuel leak from the output side of the engine driven fuel pump. No residue, so it must be a recent development. Glad I found it on the ground.

[William Hughes]

Glad to hear it help someone find an issue! Sometimes though, I read various things on the maintenance boards, and I am a little reluctant to look at my own aircraft. Still it has to be done.

[Gene Ridder]

Fitting was cracked, the portion that threaded into nut was in two parts.