Water in fuel

[Georooney]

Every fall I fill both my tanks with fuel after adding fuel conditioner. I fill the tanks right to the filler spout, eliminating any air in the tanks. (Yes, my tank vents are working.)

Every spring, like clockwork, my 90 HP 4-stroke Mercury loses power and stumbles on the first run. I change the RACOR fuel filter, and it runs fine for the rest of the season. I tried changing the RACOR before the first run, but it clogged with water and I wound up changing two filters, so now I just wait for the old one to clog up.

Two things puzzle me. One: where am I picking up the water? The tanks are full; no room for condensation. Two: why does this only happen once a season? I have two fuel tanks, so should the filter not clog again when I switch to the second tank?

I suspect the A-10 in the fuel may be the culprit. But where is it absorbing water, when the tank is right full? This fall I think I'll drain the tanks and refill them with premium fuel that as no A-10 additive. A tad expensive, but no more so than buying a RACOR every year.

Any thoughts or suggestions much appreciated.

 

[alldodge]

Maybe where you have it stored can rain water or other get into the tank?

 

[Georooney]

I thought about that, as I do store it outside. The fill spouts are on the deck; however the snap down cap covers both the fill and the vent openings. Also, as it rains all through the boating season here (not to mention sea water splashing on the deck), why is the problem not ongoing? It only happens once, at the start of the season.

 

[alldodge]

Sure is weird, buy I leave my tank where ever it is when the season ends, 1/4 to 3/4 full and don't have any issues

In any case it has to be something with that tank or its fittings.

 

[dingbat]

Ethanol can only absorb 0.05% water by volume. That’s translates into less than a tablespoon per 100 gallons of fuel.


I too store whatever is left in the tank on the last day of the season. Typically 25-35 gallon in a 94 gallon tank. Had never had a moisture issues, per say.

The one time I got water in my fuel was the result of a week of torrential rain and bad o-ring in the gas cap.

 

[SteveVT]

Maybe change gas stations?

BTW premium fuel is higher octane (ie. slower burning) if you're timed for regular. probably won't notice a difference, but maybe you will.

 

[SteveVT]

Ethanol can only absorb 0.05% water by volume. That’s translates into less than a tablespoon per 100 gallons of fuel.

This study showed the ten percent ethanol blend (E10) can hold 0.41 percent water or 3.06 teaspoons of water per gallon. This amount would equal 0.625 pints of water per 20 gallon tank.

https://cropwatch.unl.edu/documents/Ethanol and Water Contamination 09052014.pdf

 

[dingbat]

https://cropwatch.unl.edu/documents/Ethanol and Water Contamination 09052014.pdf

I agree with the findings, I had the decimal point in the wrong place, but it doesn't change the fact that you can not "condensate" enough water into the tank to cause separation. There must be an alternative source of "free" water.

In reference to the use of E0 in the link you provided...

Gasoline with zero percent ethanol can hold zero percent, or zero teaspoons of water per gallon thus any water contamination will immediately sink to the bottom of the tank. Tests by Gregory at Kettering University suggest massive water contamination is equally bad for E10 and E0 blends.

Yet outside of a large volume water contamination event small amounts of water will constantly be absorbed and safely run through an engine using E10 fuel while one using E0 could accumulate the water over time.

This would suggest that filling up with E0 does nothing for your situation. Would actually make things worst by not "flushing" accumulated moisture over time as E10 does.

Check the o-ring in the gas cap. Make sure water isn't getting in a vent line. Been there, done that....twice before I found a problem with the vent built in the fill caps.

Are your caps self venting?
Cap mounted in a recess in the hull?