Disappearing Fuel Mystery

[Tom Keevil]

Jean broke her leg in 2019, and, due to COVID closures, our boat was stuck in Canada for 2020 and 2021. So this weekend was our first cruise in a long while. Just after motoring through Dodd Narrows at slack water, while passing a huge log boom with three tugs, we ran out of fuel. There was enough wind to keep us out of serious trouble. Anchoring was impossible as the water was too deep.

The mystery is because this was so unexpected. We last filled the tank in June, 2019, and took one cruise in February 2020, just before the border closed. When we ran out, we had about 17 hours on the engine since it was last filled. The engine was run occasionally while we were gone, but that totals only about an hour. We have a 20 gallon tank which should provide about 40 hours of fuel. When I filled the tank today it turned out that there were 2 gallons still in there when the engine stopped. We had some large wakes from idiot power boaters in the narrows, so I expect we sucked up some air when the fuel was sloshing around. But the engine time plus the two gallons only adds up to about 11 or 12 gallons. What happened to the other 8 or 9?

There is no sign of leakage at the tank. There were record setting high temperatures here last summer. Could that much diesel evaporate through the vent over three summers? I pumped a liter of fuel out of the tank bottom a few weeks ago, and there was a little sediment, but nothing unusual. The fuel looked normal, and the engine ran fine. The fuel fill on the CD33 is in the starboard cockpit locker, and that was locked, so there was no access to siphon it out.

Any ideas?

[JD-MDR]

My fuel tank is on the port side. One time while motor sailing, my gauge said 1/4 tank or 5 gal. But because I was healed over so far The engine sputtered and stalled

[Steve Laume]

Whether this has anything to do with the lack of fuel or not, check the vent line to be sure it is clear. After sitting so long some critters might have clogged the opening.

If the vent was clogged when you last filled the tank, it could have given you a false indication of the tank being full. If air pressure builds up, the fuel will back up in the fill line and give the appearance of being full.

That is a lot of fuel to go missing but double check that it is not weeping out the bottom of the tank. I had to Replace Raven's tank at least 10 years ago. The aluminum tank was sitting on raw, plywood, that I am certain, had been exposed to salt water, over the years. The tank looked fine until I pulled it out for cleaning and found that it was seeping through the corrosion on the bottom.

One other possible issue may be a senior moment in the recall of some detail, Steve.

[Tom Keevil]

Steve you nailed it with the senior moment suggestion. I went back over the log and realized that I had forgotten that our engine hour meter was inoperative for much of our Feb 2020 cruise. I had forgotten that. So the missing fuel is more like 3 gallons, and I can believe that 3 summers of evaporation could do that.