How much fuel do I have?

[GordMay]

Originally Posted by hellosailor

Tom, typically a fuel tank gauge is just a ammeter set up to measure the amperage flowing through a variable resistor--which is the actual sensor. Temperature sensor, pressure sensor, whatever, they are all fairly similar although the details of each system ARE important and they are not all interchangeable.
(

hellosailor (and others) offer some good advice, excepting that most guaues are Voltmeters (not Ammeters).

ENGINE GAUGES (Fuel, Pressure, & Temperature Instruments):
Basic Theory of Operation:

There are two basic types of Engine Instrument Gauges:
a. The VOLTMETER, which requires an outside Voltage Source. This is the most common type Engine Gauge used on boats.
b. The AMMETER, which does NOT require external power.

The standard Voltmeter type Gauge receives it’s reference voltage from a Sender unit, mounted on the Engine. The Sender is a device, whose resistance varies with changes in Level, Pressure, or Temperature. As the sender resistance increases, the reference voltage transmitted to the Gauge decreases.

Temperature Senders are often Bi-Metalic Thermo-Couple devices, whose resistance decreases as Temperature rises; resulting in a higher reference voltage at the gauge. Other Senders (Level, Pressure, Vacuum, etc.) employ differing methods of varying their resistance (ie: Varisters) in response to the measured stimuli.

Alarm Switches are "On-Off" devices, either Normally-Open or Normally-Closed; which switch 'On' or 'Off' in response to a pre-set condition. Switches are utilized to operate Warning Lights and/or Buzzers.

Basic Troubleshooting of Gauges;
goto:
http://www.cruisersforum.com/forums/...sting-645.html

See also the Teleflex Tech sheet:
http://ww2.tflx.com/pdf/marfue~1.pdf

[scotte]

Originally Posted by hellosailor

"If the side of the tank is easy easy to see, you can add a sight glass to the system "
I've heard multiple times from multiple sources that a sight glass is against USCG and ABYC regulations for small craft and if your insurer finds out about it--you'll hav no insurance. Apparently they are considered a fire danger, since breaking the glass can put the fuel in the boat.

I was discussing this with our surveyor. According to him, sight tubes are fine, as long as they have metal shutoff valves at the bottom attached directly to the tank -- and they must only be opened when checking the fuel. As you say, the problem is fire danger, since if the sight tubes break or melt there a nice supply of fuel guaranteed to drain out to the height of the break.

Again, this is what he told us, your mileage may vary, lack of insurance coverage etc may vary.

[David M]

Originally Posted by sailawayjon

I think enough people have suggestions about fuel level but, I just want to say assuming were talking diesal here just make sure you dont run out that can be hours (or 5 mins) work to get that engine started again.

Newer diesels come with electric pumps that self-prime the engine should you get air in the fuel lines. Gee...why did they never think of that before?

[philip van praag]

we are very lucky and have vetus plastic tanks so its easy to see the level, and it very seldom matches the gauges.
also they dont condensate as mutch at steel tanks.
for fuel priming i have put a hand squeze belows in line, as found in outboard fuel lines 2-3 squezes and is all done.

[GordMay]

Originally Posted by scotte

I was discussing this with our surveyor. According to him, sight tubes are fine, as long as they have metal shutoff valves at the bottom attached directly to the tank -- and they must only be opened when checking the fuel. As you say, the problem is fire danger, since if the sight tubes break or melt there a nice supply of fuel guaranteed to drain out to the height of the break.

Again, this is what he told us, your mileage may vary, lack of insurance coverage etc may vary.

Your Surveyor was nearly correct - Shutoff Valves are required top and bottom.

Excerpted from ABYC Section H-33 Diesel Fuel Systems;

33.5.10 A means to determine fuel level or quantity shall
be provided. If a sight gauge is used,

33.5.10.1 it shall be equipped with a shutoff valve at the
top and at the bottom of the gauge, and

33.5.10.2 a warning label shall be placed adjacent to the
sight gauge, and

33.5.10.2.1 the warning label shall comply with the
requirements of H-33.16 .

[scotte]

Thanks for the clarification on that and the actual ABYC text to boot!

[theonecalledtom]

Thanks guys for all the great info here. I'm going to follow up on some of the advice, probably including taking off the gauge connection cover to get a visual eyeful. Photo shows the minimal access to the tank available - hopefully I'm not going to need to replace it ever as that involves removing a significant part of the cabin sole.

[hellosailor]

Tom, at least it appears that you can get a human head and eyeball above the access plate. last time I tried that--there was only room for a 3" wide head, mine was just too big to get in there. Had to pull the tank instead. (Pull battery cables, pull pedestal cables, pull harness wires, but no, didn't have to pull the cabin sole.[g])

[theonecalledtom]

Quick follow up: I tested the resitance across the float and got 60ohms back. Then I tapped top and bottom (layout doesn't allow anything in between) and got a tone difference. Finally I took the float cover off and had as good a look as I could verifying that it looked pretty full (for US float 60ohms indicates about 70% - which tallies with what the previous owners thought was in there). However I wasn't too happy with look of it though I could'n't see too well. Next week I'm going to get a sample and compare it visually with some fresh fuel.

Anyway - just wanted to close of this thread with the happy news that thanks to everyones advice I now know how much fuel I have. Thanks!

[hellosailor]

Tom-
For what it is worth...you can take a stick (or a double plastic-bagged hand) and wrap some cheesecloth on it. This is wide, very open cotton cloth sold in supermarkets and used for gathering up herbs in cooking, etc. Dip the cheescloth way down into the tank and rub it against the bottom, if there's any gunk in the tank it will stick into the open weave of the cloth and give you something easy and clear to exanine. If you can't find cheesecloth, try some old terrycloth toweling.

[mobetah]

OK .... I've got to recommend the Tank Tender by Hart Systems. Find them at www.thetanktender.com Their system uses air pressure to guage the depth of water (and/or fuel and/or sewage) in the tank. It uses no power and has no moving parts (unless you count a small air pump and pressure guage). I've had mine for over ten years and never had a bit of trouble with the system. Although when I recently replaced the fuel and water tanks, I found the tubes (which extend down into the water tanks) had become brittle .... I called Hart Systems to order some replacements and they sent them to me for fee. Now that's a good product and good service!

[Lancerbye]

I agree wholeheartedly with mobetah. I use the tank tender to monitor two fuel tanks, a water and a waste tank. It measures in two scales: inches of water and inches of deisel. You start by mapping your tank and keep a chart coresponding to each tank. The accuracy is very high and repeatable.