Diesel Fuel Overflow line

[evbeck]

Wondering if others have seen this issue. After running 20 hours under power over two days last week, we tried to put fuel in tank we were using. (Our Westerbeke 82 hp uses about 1.3 gallons per hour and tank holds 55 gal.) When we started fueling, almost immediately the diesel overflow line high on the transom started leaking diesel. Could only put five gallons in going very slowly. Has never happened before and only time the overflow line/vent ever had diesel come out was when we bought boat and overfilled tank first time.

So tank is not near full and diesel coming out of overflow line?? thanks

[tkeithlu]

Any chance you were taking fuel from one tank and returning it to the other?

[evbeck]

I was pumping diesel from pump in marina in to our port fuel tank. We do not have fuel in the starboard tank right now. So it seems like the the fuel being pumped in went into the overflow line. Very strange.

[Terra Nova]

Check that there are no traps in the vent line; that it runs continuously uphill from the tank to the transom discharge fitting.

[evbeck]

will do. thanks.

[tkeithlu]

Where does the overflow hose pick up from the tank, and is the tank vent hose clear? If the tank is not full, there's a block here somewhere. Some tank overflows are actually a branch off the fill hose, but it should go all the way to the tank and pickup from the top. If so, and the vent hose is blocked so you have an air lock, or the fill hose has an almost complete obstruction below the pick up for the vent hose, it could happen. The alternative is you've discovered the magical diesel fuel generator and should run, not walk, to the patent office. A little air pressure on the vent and overflow hoses, and suction (toilet plunger) on the fill hose should give you some guidance.

[evbeck]

These suggestions make good sense and interestingly correspond with my wife's thoughts. That's why she's the admiral and I am the captain. thanks

[boatbod]

Originally Posted by Terra Nova

Check that there are no traps in the vent line; that it runs continuously uphill from the tank to the transom discharge fitting.

yup, a low spot in the vent line will trap fuel and make filling the tank a tedious messy business.

[Bill Seal]

When we started fueling, almost immediately the diesel overflow line high on the transom started leaking diesel

How could a plugged vent line start leaking fuel overboard from the vent?

My guess is the problem is with the fill nozzle, somehow foaming the fuel or splashing it around in the top of the tank. Or maybe the vent is connected to the fill pipe instead of the top of the tank.
Just a WAG.

[reed1v]

Sure sounds like the return line can not get access to the fuel tank. Maybe a jelly plug? Or you got more than one tank and someone turned off the other tank's return feed and your current tank is maxed out.

[JOHNMARDALL]

You're doing well, my wife is the First Sea Lord and I'm a midshipman. The suggestion to blow the vent line out with compressed air, toward the tank, with the fill cap off, is a good one- the vent line almost certainly has a partial blockage or air lock. There are devices available called Splash Stops that fit directly under the deck fill and will catch foam, fill hose back up and vent line back up and return the fuel to the tank, so that it doesn't end up staining the deck or polluting the water. Naturally, I think they're a good and green investment.

All the best
John Mardall
Vetus Maxwell Group

PS Check that the vent line hose hasn't come loose and developed a low point that is holding fuel.

[Alika]

I installed a trap for diesel bubbles right at the vent line exit from the boat. It is a re-purposed water line filter. It has a drain plug at the bottom, the cylinder is clear so it is easy to look in the lazarette and view any diesel that needs to be drained off. Also plan to fit it with a desiccant in the airway to prevent moist air entering the vent line. I should patent it.
The action of the boat with a diesel tank near full will cause diesel fuel to bubble up in the vent line and even the most vertical vent hose is not always so vertical when the boat heels.

[pcmm]

My first question is WHY do you have an overflow line. seems very illegal! you're not allowed at all to overflow fuel into the water! I suspect you're talking about your vent line. I would "Dip" your tank manually to see where the actual fuel level is.

[Alika]

In my reply above, I assumed we were all talking about the tank vent line. Of course we don't have an "overflow" line.

[evbeck]

yes - it is a vent line to the transom. If we are filling tank to near full, one person stationed at transom can hear fuel coming near the vent and tell the captain to stop fueling. Only leaked a few drips of fuel once, three years ago. Not something you duplicate. thanks for the responses.