Fuel gauge not reading accuratly

[pbgeneral]

I need some advice from some of you that may have more knowledge than I do when it comes to fuel sending unit/gauge. I recently removed my 62 gallon fuel tank for draining and cleaning. I replaced the float sending unit with a new one that looked exactly like the one I took out, but discovered this week end that it is not reading correctly.
First let me say I have not filled the tank with fuel, only 60.00 to 80.00 dollars worth at a time and the gauge showed about 1/2 full, which I expected was about right, but then ran out of gas with the gauge showing 1/4 tank left. I know on install I ajusted the float all the way to the end of the arm as per the directions on the package, for the deapth of the tank I have. Now the tank is empty and the gauge is stuck at 1/4. Any ideas?

thanks
pbgeneral

 

[dingbat]

Re: Fuel gauge not reading accuratly

You need to adjust/ calibrate the lever arm type sending units to suit. If you would have bought a reed type sender, drop it in and your on your way and no more fuel gauge needle bouncing all over the place.

 

[kahuna123]

Re: Fuel gauge not reading accuratly

With the arm of the sending unit all the way down to the bottom of the tank you should read empty. If not you may have the wrong sending unit. With the sending wire disconnected does the gauge then read empty. If not then you have a gauge issue.

All that happens is the sending unit gives less resistance to ground as the arm is raised. Giving the gauge a better path to ground and therefore pushing the needle towards full. If it is already not giving enough resistance at "empty" and driving the needle too far to the the right then it is not the right unit. They are marked with the ohm range they provide.

 

[pbgeneral]

Re: Fuel gauge not reading accuratly

Thank you both for this advice. I will do some tests to see. No fun being out of gas on the water miles from shore.

 

[Outsider]

Re: Fuel gauge not reading accuratly

I wouldn't trust any gauge that was anywhere close to 1/4. Since tank capacities are measured by volume (gallons, not dollars), how many gallons did you put in the tank to get the false sense of 1/2 full ...

 

[pbgeneral]

Re: Fuel gauge not reading accuratly

I wouldn't trust any gauge that was anywhere close to 1/4. Since tank capacities are measured by volume (gallons, not dollars), how many gallons did you put in the tank to get the false sense of 1/2 full ...

Well, I put 60.00 @ 3.40 which equals 17.6 gallons, ran about 1 mile and discovered I had some engine issue, so back on the trailer it went. Made some test on the electrical system and found a bad switch box, and the trigger coil failed its ohm test so replaced it also. Then took it out for the second time did not add fuel, ran the boat about 6 miles round trip, no problems. Took it out for a third run and added another 60.00 which would be another 17.6 gallons and ran only about 5 miles round trip. After putting in gas the second time is when I had noticed the 1/2 tank reading on the gage. You say you wouldn't trust a 1/4 reading on any gage, I will not either any more. I understand I made a bad mistake in judgement, but after examination of the gage that came out and the one I put in and they are the same I assumed (we all know what that means) it would read correctly. Leasson learned. I will do as the first two post suggested and remove the gage and check/calibrate the new one. I am very aware that it is measured in volume not dollars, and am also aware that fuel prices change around the country, but I guess when you ask for ADVICE on an issue, you are subject to all types of ADVICE......

 

[jayhanig]

Re: Fuel gauge not reading accuratly

I haven't delved into a fuel tank myself in a while but the last time I changed a fuel tank sending unit, it had two limiter arms that straddled the arm with its float at its pivot point that determined the limits of travel. Those arms were bendable. Then it was a simple matter of adjusting them so you could tap the arm against the top and bottom of the tank. That is preferable to bending the arm because you could adjust both limits, not just empty.

My big question is: with the tank empty, does the float touch the bottom of the tank? If it doesn't, the gauge will obviously continue to indicate fuel that isn't there. You'd need a different sending unit in that case.

 

[NYBo]

Re: Fuel gauge not reading accuratly

The problem could be the fuel pickup tube. It might not be reaching the bottom of the tank.

 

[kahuna123]

Re: Fuel gauge not reading accuratly

Its very simple. The arm moves a variable resistor. The further down the arm is the more resistance the sending wire (gauge) to ground it sees. There are different "ranges" of resistance depending on which gauge you have. The sending unit and gauge have to match. IF and only if the sending unit arm is ALL the way down and it is still allowing to much current flow to ground and making the gauge read too high you have the wrong sending unit. Also all the way up it needs to decrease the resistance to ground enough to make the gauge read full. Some of them are adjustable but if you are starting out with not having enough resistance with the arm all the way down it will never read correctly. Most never stuff is all the same ranges. Some of the older units used different ranges. Also make sure the gauge and the tank-sending unit have good common grounds or you can get really weird things happening.

Don't go down the path of how big the tank is how much you put in. The sending unit doesn't care how big the tank is. All it does is allow less or more resistance to ground depending upon the height of the arm.

 

[NYBo]

Re: Fuel gauge not reading accuratly

I would still want to verify that the tank is actually empty, or nearly so.