Fuel tank sensors don't work

[gilligansail]

I have US sensors with Blue Sea Systems and they are inaccurate despite multiple attempts to calibrate

Any advice on the best sensors? Or how to solve this problem?

Thanks

[Sailmon]

I have a Blue Sea sender and electric fuel guage on our sailboat. Not sure if this is relevant to your (inaccuracy) concern - but after 10 years we finally figured out why the first half tank of diesel fuel lasted so much longer than the second half tank, and why, when fueling up, the 32 gallon tank always took more than 16 gallons to go from half empty to full. Turns out our tank is not a symmetrical box but is tapered along the bottom to follow get curve of the hull. Consequently, the footprint of the tank bottom is smaller than the dimensions of the tank top - so the top half tank is larger than the bottom half tank. Since our tank sender is a vertical measure of tank contents it does not take into account that the top half of the tank is larger than the bottom half.

[belizesailor]

Get a pneumatic Tank Tender system and be done with it. Can also be calibrated to irregular tank shapes.

Super reliable too...Ive had the same unit for about 20 years over 2 boats now.

[awaywego]

I second the Tank Tender system.

[Sailmon]

Nice thing about tank tender is they sell systems that monitor multiple tanks - water, fuel, waste...

[ranger58sb]

I have CruzPro **-60 fuel gauges (the more expensive version of their two), mated to WEMA/KUS senders in two 262-gallon "right trapezoidal prism" tanks.

I've calibrated those "by math" versus their recommendation to start with empty tanks and let the gauges "learn" the correct quantities. I imagine boats with small tanks could do this, but I don't have a way to start with empty tanks, and don't have fuel docks around here that would let me fart around for the time it would take to teach the gauges.

OTOH, small tank? Maybe not difficult.

The gauges may or may not be accurate, yet; I haven't yet had more than one opportunity to fill the tanks (since installation) to check my calibration.

I can say they are NOT perfectly accurate while we are underway, since fuel moves to the rear of our tanks and that in turn raises the float on the sender. Which in turn means the extra calculations/displays offered by the **-60 gauges are generally only useful at rest, if at all.

All that said... if you have a relatively small -- and irregularly shaped -- tank and can go through their recommended process, the **-60 could be worth a look. OTOH their F-60 would likely be adequate with a cuboid tank, and it's dead easy to set them up (I tried them, too, before returning to the **-60s). In either case, I think the weak link is the sensor technology -- and "accuracy" is a relative concept.

-Chris

[wrwakefield]

Originally Posted by gilligansail

I have US sensors with Blue Sea Systems and they are inaccurate despite multiple attempts to calibrate

Any advice on the best sensors? Or how to solve this problem?

Thanks

As Chris mentioned, the Cruzpro gauges will be the electronic way to gain additional accuracy from your existing sensors.

But dip sticks and/or sight gauges don't lie...

I have fuel sensors and sight gauges on both 130 gallon tanks. The sensors let me know fuel is splashing around in the tank; the sight gauges tell me precisely how much...

Neither tank is accessible, so each has a pipe nipple- with a valve on the end- extending into accessible space.

Each sight gauge has a valve at the bottom. The top can either have a valve or tie into the tank vent line.

I only open the valve when taking a reading, and leave it closed the rest of the time.

The gauge is a clear, fuel proof 1/4" ID tubing zip tied to a 1" wide aluminum bar that is mounted top and bottom. The aluminum bar has the calibration marks on it, so it doesn't matter if the tubing slips around in the multiple zip ties holding it to the bar.

Calibration at the desired increments [10 gallons in my case] needs to be performed carefully, but only once.

Both are in the engine room and reading them is part of the pre-flight checklist...

In case this is helpful...

Cheers! Bill

[sailormed]

I know my fuel level gauge is inaccurate. So I just keep track of "tank hours", i.e. the number of hours the tank has fed the engine since my last fill up. And reset to zero whan I fill up .

[CaptTom]

It strikes me that a reliable, inexpensive tank level display system would sell pretty well. There are reliable systems, and inexpensive ones. But I've yet to see one that fits both criteria.

Until then, sticking the tanks works well enough that I can't justify the cost of a good multi-tank solution.

[Jolly Roger]

I recently removed my boats original water tank gage system, circa 1977, which was the fore-runner of the current Tank Tender method. It relied upon pneumatic (air) pressure change in a tube in the tanks which registers on a dial. A problem is that the slightest air leak anywhere in the connecting tubing can cause errors or complete failure.
Any tank which follows the shape of the hull, as in most sailboats, will not register the actual capacity of the tank, which after all is what we need to know.
Therefore any system, be it sighting glass, swing arm, or pneumatic reading, will need to be calibrated by first filling the tank 1/4 full and marking the dial or tube, then ½ full, and so on.
Wema. Inc. www.wemause.com make an electric system, (which has no air leakage problems), and who can calibrate their floats to the actual capacity of a triangular tank.
I now know when my dial reads 1/2 full, it actually means half the capacity of the tank, etc. They also have a multi tank dial for up to seven tanks, for both water and fuel and are about half the cost of The Tank Tender system.
I have no affiliation whatsoever with Wema, and an article about how I changed out my fuel tanks gages will be published in Cruising World some time this year.

[Stu Jackson]

How come you don't know your fuel consumption and tank size? Why do you need an automobile fuel gauge. They are horribly inaccurate on boats. For the past 19 years I have kept a detailed record of my fuel use, 0.5 gph. All I need to know. You can do it too.

Fuel Log

[Nicholson58]

We gave up on all gauges. I filled 5 gallons at a time and calibrated a stick with notches and numbers. It is always right and consumes zero power.

[belizesailor]

Originally Posted by Nicholson58

We gave up on all gauges. I filled 5 gallons at a time and calibrated a stick with notches and numbers. It is always right and consumes zero power.

The Stick is a good option if workable on your boat, but unfortunately for many sailing vessels its not feasible.

[ranger58sb]

Originally Posted by Jolly Roger

Any tank which follows the shape of the hull, as in most sailboats, will not register the actual capacity of the tank, which after all is what we need to know.

FWIW, the CruzPro **-60 is designed to do exactly that, according to them. Said to work with any normal sender (I can say it worked with Stewart-Warner and WEMA senders).

"Teaching it" the tank shape/capacity was the only difficult part for me; not easy to remove 500+ gallons of diesel to start with empty tanks...

So I resorted to math to calibrate. At least in my case, the tank capacities at various resistance levels (sensor float heights) were more easily calculate-able because our tanks don't have any curved sides...

But given a small tank, calibration using their recommended method (starting with an empty tank) should be easy.

-Chris

[Jacana]

Instead of tank gauges install a clear hose on fuel line at bottom of tank and fasten other end above top of tank to get accurate fuel level by sight on clear hose.