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Water in the Fuel Tank

R

RFSchaller

Well Known Member
I washed the plane today. The last time I got water in the fuel tank through the cap vent so I taped over the cap thinking that would prevent contamination. It didn't. I still got half a test tube of water out of the gascolator after a 12 minute run. I'm posting this just to let everyone know how easy it is to get water in the tank during a wash. Good news is the water seems to pass into the gascolator quickly rather than roll around in the tank.
 
I think this deserves a bit more detail...

You taped over the cap but think water still entered the tank while washing?

So what should we assume...

You are a real lousy cap taper? :D
You used real lousy tape?
That water was already in the gascolator when you started the wash job?

???
 
Yep, that would be my conclusion but it sure surprised me as I thought I had 3/8" contact with the skin all the way around the cap. Moral of this story is the vented cap is susceptible to water intrusion. Check carefully after rain or washing. I did a 12 minute run and got half a tube of water. Another 12 minute run resulted in small bubbles of water. I'm going to repeat the ground runs tomorrow to be sure it's all out.
 
Perhaps just as dangerous as water in the fuel is forgetting to remove the tape from the fuel cap. One more reason to install the new optional vent.
Joe Gores
 
Don't know if this is the case on your fuel cap or not, but I found out an interesting tidbit when I completed the recent fuel tank SB. While leak testing the modification, I was having trouble getting a good seal. Soapy water quickly identified the problem that the fuel cap was not sealing in the down tube. I had adjusted the fuel cap to make it a little easier to get the cap off. It was still pretty friggen tight, but it was still leaking around the cap. I had to tighten the cap further to really squeeze the o-ring. I also lubricated it with fuel lube.

Moral is that if I flew in some rain, it would have let water in around the cap. Not good.
 
I have noticed my cap not fitting well also. It appears that in manufacturing they used some sort of preservative coating, that congealed into almost glue like material. I have not determined just what to use to clean the goo off without ruining the O ring (or if I just need to get a new O ring). Has anyone else encountered this?
 
DonFromTX said:
I have noticed my cap not fitting well also. It appears that in manufacturing they used some sort of preservative coating, that congealed into almost glue like material. I have not determined just what to use to clean the goo off without ruining the O ring (or if I just need to get a new O ring). Has anyone else encountered this?
Click to expand...
Yes. And it can be quite burdensome if you're buying gas for the first time in a few weeks. Mine was stuck on there pretty solidly. I also had the same question: can I remove it without messing something up?
 
The o-ring is made of Viton. Products you may have, gasoline, with or without ethanol, jet fuel, Isopropyl alcohol are compatible. Do NOT use MEK or acetone.
 
I don't know if the water came in through the vent hole in the cap or around the O-ring. Like I said earlier I just wanted to let folks know intrusion seems to happen with a vented cap. Here in Arizona rain is usually not an issue, but on cross country after a rain I'll be doing a short run and gascolator check in addition to the initial gascolator check. I guess this is a good illustration as to why the fuel tank drain mod is a good idea.
 
Couple of observations. Did new o rings from Van's including stem. If tank is overfilled, fuel squirts out the cap. So there is no perfect seal. Nut is tight and good expansion present. The carb overhaul guy has some o ring lube that stays in presence of fuel but he says it is deadly if mishandled. Fuel lube has the wrong name. It is not lube. It is a thread sealant. Tried it a few time on primer o rings. Initially it lubes but then gums up the works. Must be somebody on here that can name a proper lube that is safe and works and does not wash off with av gas. Engine faltered on climb when I first brought it home. Heart rate spiked... Found a drop or two of brown looking rainwater in right tank.
I over sample now, but at least I put the good gas back in the tank. In the old days it went you know where. :)
 
The position of the cap o-ring in the filler tube is one cause of water migration into the tank. The filler tube interface with the filler tube flange upset is at the same depth as the o-ring. Compounding the problem is the weld combining the two parts. O-rings need a reasonably smooth bore to achieve a 100% seal with minimal compression. Vans should extend length of the filler flange upset by 1/2" eliminating the uneven surface.
 
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