vapor lock and impossible turn today

This particular location has a 5,000 gallon tank in an underground concrete locker, not truly a buried tank. He services 10 aircraft with that fuel and it gets a new delivery about every 4-5 months so age is not much of a factor. And yes, if you crunch the numbers that's some high fuel burn, but some of those birds are thirsty twins and at least one helicopter. I don't know when the last inspection was but I'll ask.

The more I roll this incident over in my head the more I'm inclined to think it was water that settled after I sumped and not vapor lock. I'll be more vigilant in the future with this fueling location for sure.
 
Did you drain the fuel strainer, or did you just sump the tank? I have seen major corrosion in strainer bowls, indicative of strainers that seldom get drained. If it fills with water it can't prevent that water from getting to the engine, and if it was already full it needed only a few drops more to make trouble.

The newer 172s have the boost pump under the floorboards under the copilot's feet, right at the lowest point.

Vapor lock in high-wing airplanes is rare indeed. The head pressure of gravity is enough to prevent it.

Those newer 172s also have 13 sump drains. Five in each tank, to get all the water that comes up against internal stiffeners, one under the selector valve on the belly, one under the header tank (also on the belly) and the fuel strainer. Got to get them all. The header is there to get the return fuel that has bubbles in it.

And a sticking valve is a definite possibility. Is this a rental that get flown full rich much of the time?

One further possibility: There were a number of fuel distributors (the thing that divides the fuel four ways, to each cylinder, and sits atop the engine) that were manufactured with too-tight clearances. The shutoff poppet can stick, and usually shows up as a hard-starting engine in cold weather. Should be an SB on it on Precision Airmotive's website.

Dan
 
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On this run I sumped the low point on the tanks only, though you have a valid point about water accumulation. I don't have 5 drains on each tank, there are only 3 if memory serves. This is not a rental, we baby this airplane and lean it harshly while on the ground and slightly less harshly in the air. Pretty much the only time the mixture goes full rich is for start and short final, and WOTLOP cruise is SOP. We've never had anything happen that even remotely smelled like a fuel divider issue, in 600 hours of operation over 2 years.

Since the last update it's made two more trips for 5.5 hours with no sign of any hiccup, and I'll put another 4 on it tomorrow, then it goes in for annual. We'll have our A&P go over it carefully to see if he finds anything.

I guess realistically, given my experience with rental aircraft, I've become spoiled and should just be happy that in 600 hours of operation this is the FIRST TIME I've had anything happen in this airplane that I didn't like. Life is good! :yes:
 
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Lots of good information. I've had a rough running engine and surges after hot starts in my Mooney. I think I'll try running the boost pump next time it happens and see if it helps. One issue I had years ago concerning take off and then the engine running rough was caused by some material embedded in one of the spark plug electrodes. The take off was at near sea level and full power applied. Shortly after take off the engine ran terrible and shook. Fortunately the plane limped around the pattern to do a safe landing. It was a Experimental W-8 Wittman Tailwind. To duplicate the condition, I tied the plane down, ran the engine to high power and started leaning it to get it hot. It ran terrible again and a mag check didn't clear it. I had to lower the power and enrich the mixture to cool it to get it running right. It turned out that the junk in the spark plug was acting like an ember when it got real hot and fired out of time. If this ever happens in flight. reduce power and enrichen the mixture, then turn off one of the mags and reapply high power and lean. If it happens again, do the same thing to cool it off then try the other mag and reapply power and lean. This might save you and your airplane someday when something gets embedded in one of the electrodes. I wonder how many planes crash due to this. sorry about the long post. -- Darrell
 
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Careful...
 

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I cannot speak to what the EPA does with underground tanks in other states but in VA. It is largley left to the tank owner to care for thier tanks. Tanks 40 to 50 years old are not uncommon. Line leak tests are required yearly unless it is a suction pump rather than an in tank pump. Anode tests are yearly and water monitoring is required. Tanks with water are common and having he pickup point 1 inch off the bottom of the tank is common as well. You could easily get water or debris from these tanks. Filters commonly used on older pumps will catch most of the particulate matter but will pass water. Hydrasorb filters will restrict to a very slow flow if they get a load of water. I have seen underground tanks with fifty gallons of water after a heavy rain when a fill cap is worn or not locked down. In addition there are many tanks the EPS knows nothing about. I have one questions, was the fuel Avgas or unleaded auto fuel ???. If not Avgas it is entirely possible the tank got a load of gas with ethanol in it and it will phase seperate very quickly with any water in the tank. The result is water in your fuel and very low octane which makes an engine run like crap. That is not likely the cause as it would not clear up until the fuel was drained and replaced most likely, but it would be more prone to vapor lock. While I do not claim to be an expert in his field, 14 years of working on these things has taught me a lot. You really would not believe the dumb things I have seen done with fuel. Mistakes happen with the best people and more often to some others. I have even seen an airport with 75 gallons of water in their Avgas tank. Great job and glad you and your father are safe.
 
Tom-D said:
My thoughts as well, I have never seen a vapor lock in a 172, I have seen venting problems that prevented the proper fuel flow out of a tank.

A vapor lock requires that the fuel lines have a high point in the system between the tank and the gascolater to trap air, the 172 does not.
Click to expand...

A fuel injected engine can vapor lock in an injection line or the spider.
 
Glad everything worked out. Sounds like some water got into the system.
 
If this was a water incident wouldn't the strainer still have water in it after the problem?
 
Great job. Thanks for passing the story along. It validates the situation I've briefed 100s of times without really understanding what could possibly happen.
 
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water is more likely than vapor lock . . . . the boost pump would have overcome that . . .
 
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