E34-2 Fuel Tank Size [Volume]

Phr3d · Jul 2, 2024

How accurate is the gauge to guess for gallons on filling? How large should my tank be?

Sailboat data indicates 30 gallons.

Gauge showing almost 2/3 full was 8 gallons in San Diego.

Gauge showing something like 1/3 full was 12.8 gallons today.

Is it possible I have a 20 gallon tank?

Or is it really 30 and the gauge is crazy?

sdwnav · Jul 2, 2024

Couple of thoughts for you.

The boat’s heel and trim angles will affect what the gage is reading.

Gages are reading the liquid height. So if the bottom of the tank is shaped to the hull it isn’t going to have as much volume as the upper part of the tank. Think of the gage as reporting liquid height not volume; the relationship is not going to be linear if the tank has shape.

peaman · Jul 2, 2024

The stock gauges can only give a very rough idea of how full your tank is. Here is what you should do:

Empty the tank either by running at or nearly out of fuel, or else, get it low enough to pump the remains into a separate container, ideally one whose volume is known. Then, add fuel into the tank 2, or 3, or 5 gallons at time, and with each increment, make a mark on the tank or gauge, or make a note to show the correlation between actual volume and gauge reading. That way, you can better estimate how much fuel you actually have, in spite of the gauge's poor reporting.

Christian Williams · Jul 2, 2024

Since the boat is new you'll have to figure this out. Start with the listed 30g for your model.

As Steve said above, most of our tanks are shaped to fit the space, meaning wider top than bottom. Therefore, typical fuel gauges are only rough approximations, since there's more fuel in the top half than the bottom half.

I would remove the fuel gauge from the tank and sound it with a dowel through the open hole. That will at least give you a gross reading of half, one-third, etc.

The only way to confirm your actual tankage is to pump out the tank, then fill it full. But since the fuel burn is so low on our boats, most of us are content with a rough estimate. Sounding the tank once will relieve concern about no fuel in there at all.

It is useful to add your engine to the Signature line.

bgary · Jul 2, 2024

Phr3d said:
How accurate is the gauge to guess for gallons on filling?

Probably not a direct (or maybe even useful) answer to your question, but... I don't trust gauges. I trust fuel logs.

When I got my boat I started keeping track of engine hours, and (later) the amount of fuel required to refill the tank.

What I learned over time is that my boat averages a little over 1/3-gallon per hour. And I know when my tank is as low as I've ever let it get, it took a little less than 17 gallons of fuel. In what is (theoretically) a 22-gallon tank.

How much fuel was still in the tank when I was down 17 gallons? Don't know, don't care. Maybe it was 5 gallons, maybe it was nothing but sludge and fumes. I try not to put myself in a position where I'll have to find out.

What I do know is that I can go about 48 hours (call it 300 miles) before I'm in the mystery zone. And by keeping track of engine hours between fill-ups, I know (with reasonable confidence) how much of that known-good 17 gallons I've got in the tank.

$.02

Christian Williams · Jul 2, 2024

Yes, all you have to do is note the Hobbs meter when you add fuel. A Hobbs meter, or hour meter, is just a clock that runs only when the ignition is on.

Private pilots are taught never to trust fuel gauges, since running out of gas is ,uh, bad. All calculations are fuel burn.

Loren Beach · Jul 2, 2024

Our new tank was spec'd out with a new Wema analog electric gauge that I mounted at the main panel area. The sender was their standard top mount one for the tank and was installed by the fabricator.
Seems to work reliably. There is really just one big caveat , however. As others have noted, these devices do not tell the amount of fuel remaining. Only the level. You do have to learn to inerpret that information. Like most others, we understand that "1/4" on the gauge means less than that.
As noted by wise mariners, maintaining a little engine-hour time and amount-added log is still the best way to be sure.
Also, I did add a "Hobbs" meter when we did the repower, since the digital engine hour panel readout, in the cockpit, is difficult to see.

O34 - New Hour Meter & Halon Status light (part 1)

After removing the old (crumbling lens) Halon status light in its escutcheon plate, I needed to install a new one. The purpose of that light is to see if the Halon extinguisher has discharged, without opening the hatch to the engine compartment...

ericsonyachts.org

(And did indeed source that meter from a vendor rightly concerned with their customer's planes needing very accurate information... "Aircraft Spruce & Specialty".) Pictures in my engine swap blog.
I bought the DatCon mini, https://www.aircraftspruce.com/catalog/inpages/datconhobbshrmeter_10-05542.php?clickkey=10669740

JSM · Jul 2, 2024

Our 34-2 was built in 87 and the mfg label on the tank says 27 gallons.

HerbertFriedman · Jul 2, 2024

I agree with the Hobbs method, I refill the tank on my 87 E34 every 15 hours and it usually takes 5 gal, so the 1/3 gal/hr seems accurate. I fill the tank to overflow and catch the overflow out the transom mounted vent in a bucket, but the after that, the gauge usually reads "full".

Marlin Prowell · Jul 2, 2024

I created a CAD model of our E34 fuel tank to confirm how difficult it is to use a gas gauge. The tank has a notch in it and the fill hose and vent hose are connected to the back vertical wall of that notch. The volume of the tank with the notch is about 28 gallons. If the notch did not exist the volume would be 30 gallons.

Because of its shape, 15 gallons fills the tank up to the bottom of the notch. The top 2-1/2" of the tank that has the notch holds the other 13 gallons. In my boat, the fuel sender is mounted down in the notch, not on the top of the tank. The fuel sender float has a big upward bend in it so it can maybe reach the top of the tank when there is more than 15 gallons in the tank. It is vey inaccurate.

Phr3d · Jul 3, 2024

Phr3d said:
Gauge showing almost 2/3 full was 8 gallons in San Diego.

Gauge showing something like 1/3 full was 12.8 gallons today.

I apologize. Ya'll probably caught this, but while I was trying to type this question in a boat reeking of diesel in the cabin (the tank was definitely overfull, bubbling from around the gauge), I was confused, angry about stinking up my boat, and little bit high from snorting diesel fumes.

Those sentences were the results of filling the tank. I put in 8 gallons when the gauge showed around 2/3, and 12.8 gallons when it showed around 1/3.

The math makes me think its like 24? So the 27-28 makes sense.....

Now making sticky to get/keep an journal to monitor engine use.

Christian Williams · Jul 3, 2024

First you'd better pump out a few gallons and reseal the gauge against further leakage. You will probably need a new gasket, and I recommend some sealant too. If the tank is brimming, it will continue to leak through the gauge seat as the boat moves in the water.

And get the diesel out of the bilge.

Phr3d · Jul 3, 2024

It looks like the die

Christian Williams said:
And get the diesel out of the bilge.

It looks like the slow filling of the tank (I was hanging over the lifelines trying to keep my core engaged, an eye on the vent and an ear on the tank gurgling) resulted in no spills. When I pulled up the aft cabin cushion to look at the gauge, I could see air was venting, but no liquid. I put one of those absorbent cloth things over the area. When I removed it, there was some pink residue, but not even enough to discard the cloth. There is no longer diesel smell inside the cabin.

I like the gasket idea. Is there one commercially available or do I make one?

Christian Williams · Jul 4, 2024

See Post #7:

Oh dear air vent, why doth thou leak?????

It started a few years ago when my boat destroyed its tether and ran aground, resting on the diesel intake side. I noticed some leakage and cleaned it up. A consult with help said that sometimes the diesel will flow out of air vent at that extreme angle, and apparently elsewhere since there was...

ericsonyachts.org

JSM · Jul 4, 2024

I had my tank out last year for cleaning. When I reinstalled it I added five gallons of fuel, went below and marked the tank at the position of the fuel indicator. I then added another five gallons and marked the tank again.
I know have a better idea of how low I am as well as how much I can add without overfueling.

Teranodon · Jul 6, 2024

Christian Williams said:
....most of our tanks are shaped to fit the space, meaning wider top than bottom. Therefore, typical fuel gauges are only rough approximations, since there's more fuel in the top half than the bottom half.
...
The only way to confirm your actual tankage is to pump out the tank, then fill it full. ...

The scale of the mechanical gauge on my tank is highly nonlinear, and gives a good measure of how much fuel is there. I rarely go to the fuel dock, but bring 5-gal cans to the boat, checking the gauge before and after, so I can confirm this. My tank is 20 gallons, but it isn't original.

In general, I would not recommend running the engine dry. Bleeding those injectors is a nuisance.

Phr3d · Oct 31, 2024

So, the answer was under the tank cover - 27.8 gallons

Phr3d · Dec 16, 2024

The hourly method resulted in almost a third of a gallon an hour.

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