Fuel gauge off, bad.

[Pontoonfoon]

Ive read a few threads where people say theirs reads empty after using just a few gallons, my problem is not that bad and (In my opinion) different.

I have a 30 Gallon tank, and my gauge reads as follows, the left amount being the actual fuel amount, the right amount being what the gauge indicates.

Full - Full

6/8 - 3/4

3/4 - 1/2

1/2 - 1/5

1/3 - E

1/4 -E needle all the way down.


I pulled everything out of the tank and don't see anything that looks bad.. not that i really know what to look for.... nothing looks OBVIOUSLY bad..

any ideas?

it wouldn't bother me much, since i know what equals what for the most part, but with less than 1/3 I don't.. it just says totally empty.. so I might have 9 gallons.. and i might have 1.. not safe..

 

[EricJRW]

Re: Fuel gauge off, bad.

Has it always been this way or has this problem developed over time?

The reason I ask is the sender must be paired with the correct gauge, as the gauge must be calibrated to the sender (based in the range of resistance values the sender will send for the various levels). If the gauge has always read incorrectly, then this is what I would suspect.

If it's a new problem*, then I don't have any answers.

* PS - Was reading in another thread where the float on a fuel gauge had gone bad. If it lost buoyancy, I would suspect the readings would always be low. I'll see if I can find that thread.

Here it is: http://forums.iboats.com/showthread.php?t=434950&highlight=gauge+float

Well that thread was not as helpful as I recalled, but it might get you on the right track.

 

[Kaplooi]

Re: Fuel gauge off, bad.

What's the vertical dimension of your tank, just out of curiosity? I understand shallow, below deck tanks can be notoriously inaccurate due to the small amount the float moves vs how much fuel is in the tank. In my case I had the opposite situation with a deep tank that always read low. I believe the resistance on the senders tends to increase over time reflecting the false low readings. I ended up removing the sender and just bending the float rod down so it read higher. This only worked because the rod and float were not at the top of the pendulum on the sender's slide sensor thing. You can try the bending the rod adjustment but it looks like your readings begin accurate and get progressively worse, so a new sender is probably in order. Like EricJRW said it needs to match the resistance the gauge is expecting as well as your tank depth or else it could be off worse than your current one. The only way to calibrate that I can think of would be to inline a resistor to do a mass correction or to bend the rod like I mentioned above. The 240ohm senders are fairly common, but that's just a guess

Of course there's always the overly expensive flow meter solution

 

[dingbat]

Re: Fuel gauge off, bad.

Of course there's always the overly expensive flow meter solution

Or buy a inductance type fuel lever sensor and be done with the floats, arms, deep tank, shallow tank stuff alone with the wild fluctuations in your fuel readings.

Those reads are not very linear so I'd pretty much would rule out a misadjusted float. The easiest way would be to put a meter on the output of the fuel sensor and see how a full swing of the float reads. The readings should be very linear from the top to the bottom of the stroke. If your reading are good from top to bottom, then I would suspect your gauge is the problem.


What's up with the 6/8 vs. 3/4?

 

[EricJRW]

Re: Fuel gauge off, bad.

What's up with the 6/8 vs. 3/4?

Good catch!

 

[Pontoonfoon]

Re: Fuel gauge off, bad.

What's up with the 6/8 vs. 3/4?

LOL


beer..

 

[DJ]

Re: Fuel gauge off, bad.

One thing to consider. Boating Mag. did an article on this subject about a year ago. You can Google it.

Try turning, if you have the room, your fuel guage (tank) sender 90*. That will give you a better sense of your real fuel level.

You have to realize that a boat fuel tank is always at some sort of pitch, rarely level.

 

[Silvertip]

Re: Fuel gauge off, bad.

Fuel senders can be adjusted -- fuel gauges cannot. If you look at the sender float arm you will see that the float itself may be movable. That's one adjustment. Bending the float arm can adjust the low end of the scale, the mid part of the scale or the top end of the scale. It cannot be bent to adjust all three. So bending the float arm and adjusting the float can result in a little more linear movement of the fuel gauge but the very nature of its design is not linear. So the logical adjustment is to adjust the gauge so when the tank is empty (or near empty) the gauge reflects that. You know when it is full when you fill the tank. You also need to understand that a fuel gauge is a fuel "level" gauge, not a fuel "quantity" gauge. Consider a cone shaped cup. When the cup is half full, there is much more fuel at the top half than the bottom half. Your fuel tank, although not cone shaped, is usually wide and shallow so it is difficult to achieve real accurate indications. Therefore you want to know when the tank is empty -- full is of lesser importance.

 

[thaphillips]

Re: Fuel gauge off, bad.

Or buy a inductance type fuel lever sensor and be done with the floats, arms, deep tank, shallow tank stuff alone with the wild fluctuations in your fuel readings.

Those reads are not very linear so I'd pretty much would rule out a misadjusted float. The easiest way would be to put a meter on the output of the fuel sensor and see how a full swing of the float reads. The readings should be very linear from the top to the bottom of the stroke. If your reading are good from top to bottom, then I would suspect your gauge is the problem.


What's up with the 6/8 vs. 3/4?

Could you post a link to a inductance type fuel lever sensor?