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persistent water in fuel

Jake14

Well Known Member
Never had any water problems in several years, but after replacing a cap (SPRL) and some freezing rain a lot of water appeared in the left tank. Put the old cap back on and sumped the tank till all was clear (took about 4 test tubes full of water to get clear). The problem is that some water seems to remain in the tank even after sumping. With the tank sumped and clear of water, after a short flight (or in one case, just taxiing), sumping shows 1-2 in of water in the test tube. Get rid of the water, take another flight and the water is there again. This has happened 4 times with the same fuel load over a couple of weeks. If I let it sit for a few days after sumping, there's no water in the tube, so it seems the motion of flying the airplane causes water to flow down to the sump.

Is this normal for RV tanks (these are QB) after a lot of water has entered?
 
Don't fly it.... Shake the wing. Let it settle and then sump. Repeat until there is no more water.

If parked outside, get some static cling material and place over the fuel caps. Tape down if needed.

On my 6A, it would take over 6 oz (not much) of water to reach the pick-up tube.
 
Change in temperature, especially dropping, can create a low pressure in the tank and help suck in water sitting on the surface. Perhaps the vent tube setup is not working well ? Of course if the cap didnt seal and things were wet for a while, who can tell how much water got in ? But lack of pressure equalization or the ability of precip to enter the vent tube (and potentially freeze, blocking the line) would not help.
 
Agreed that you shouldn’t fly it until you can get it out.. Rock the wings, then hold the wing in question “up”. Sump. Then pull the tail down and sump.. keep repeating until clear. Perhaps the SPRL caps can be lubed and adjusted like the older ones to prevent water from leaking in?
 
Are A models more apt to retain some water trapped from getting to quick drain due to its static attitude?
 
I had a similar, very frustrating, experience. Would sump an inch or so of water, then the engine would stumble. Did this three or four times. What I hadn’t done was sump the gascolator….. Turned on the Boost Pump and sumped the gascolator, almost a full tube of water. No issues since…. I had read that it isn’t necessary but now i sump the gascolator every flight.

It seems, and someone may correct me on this, that water would settle in the gascolator then during flight small amounts of water would occasionally mix back into the fuel and I’d get a quick stumble.

Two cents…
 
Water sinks to the bottom and each rib acts as a stop for the water and there are only a few openings for this water to get past. It takes a good bit of agitation to get the water to those openings so it can make it to the sump drain. Get the cap seal sorted out and keep draining after each flight until it is gone.
 
Water

Agree with the above comments. Consider that the quick drain is a small opening and the sample tube or cup is a small amount. On my planes I rarely see anything from the quick drains, but every 24 months or so I take the quick drains out and drain 1 or 2 gallons into a clean bucket and usually see a little water or debris. The larger opening and volume will move contaminates out of the tank better. If chasing a water in the tank issue I would go further and get the offending wing and nose higher than normal before taking the quick drain out.

CAUTION & DISCLAIMER: Any advice or opinions are worth what you paid for it. Be smart, All fuel handling precautions apply. Ground the plane and container together and to a common ground point outside and away from other planes. Fire extinguisher 🧯 at the ready, ect ect

Don Broussard
RV9 Rebuild in Progress
57 Pacer
 
Thanks for all the great insights and suggestions. This has been a very puzzling issue. FI and no gascolator. At least 5 flights where the sump has been clear before flight and 1- 1.5 in of water in the tube after landing (flying on the other, good, tank) I've shaken the wing, lifted it up and held the tail down to the ground for about 2 min, and no signs of water in the sump until after the flight. Maybe there's a lot of sealant around the ribs with pockets for the water to hide? Anyway, it's pretty much gone now.

Wondering what may have caused the original large amount of water in the tank, I'm thinking that the ice storm event where the wing had about 1 in of solid ice on it may have also plugged the vent and caused a slight vacuum in the tank when the weather warmed which pulled water past the small o-ring on the SPRL cap shaft. I really like the SPRL caps and they've never given me any trouble. if you twist the cap as you lower the tab, you can feel the o-ring seat in the collar. The one downside is that the center o-ring on the shaft is below the wing surface, so when it rains the water pools in the recess above the o-ring, but if it's properly greased and there's no pressure differential it's probably ok.

Thanks again for all the help.... I'm going to be doing a lot more sumping in the future :)
 
Might be time to investigate the weep holes in the tank ribs; make sure they're there and not full blocked. Mooney aircraft had an AD or SB on such. Not only was water engine ingestion a problem, it was causing corrosion and eventual tank breaches. They had a sealant "candy coat" on the skins, RVs don't.

Borescopes are cheap and/or borrowable. Just a thought for some peace of mind.
 
Definitely plan on looking inside the tank..Never having done this before are there any safety precautions for dealing with fuel vapors or using LED (borescope) lighting inside the tank?
 
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