Fuel tank sending unit question- best if the float is on the tank bottom or below the fuel at full?

[PDQ]

This is for a NWMP aux tank and a new WH sending unit for the same, and the sending unit float arm can be adjusted as a sliding arm on the pivot point, so if the float is adjusted to be at or nearest to the top of the tank at full, it would then physically rest on the tank bottom at empty, or I can adjust the float arm to be just above the tank floor at empty, but then it will be about 1" below the liquid line when full.

I don't think I want it banging around the bottom of the tank at empty, but also, have to believe that if the float is submerged while at a full tank for any period of time, it will eventually fill with fuel and be useless.

Any thoughts on what the better adjustment setting may be?

Thanks as always.

 

[Wild horse 75]

Below the fuel at full. Hitting the bottom of the tank means you are EMPTY when it reads empty. Always safest to have a bit of reserve when the gauge reads empty.

 

[ba123]

You can always get a different sending unit as well.

The marine style works SO much better. They have them on Amazon, just make sure you match the resistance range for your gauges if stock

Which NWMP tank?

 

[PDQ]

Great point WH75

ba123, it's their 12 gallon metal aux tank

 

[DirtDonk]

I say no matter what you end up doing inside the tank, connect it to your gauge first, and test that the range in question actually reads correctly, or as expected, on the gauge.
That way, you’ll know if you need to make any tweaks, that you might not have been expecting from just the install part.

 

[Steve83]

What's more important to you? Knowing that the tank is exactly full? Or knowing when it's empty?

 

[PDQ]

Thanks all and I do get that how full or empty it reads can be a preference and the sweep should be checked first, but I guess what I really wasn't sure of, was that if th3e tank was full and it were to be adjusted to where the float was actually submerged until such time as the fuel level dropped, would the float eventually fill with fuel and lose it's buoyancy? I would think not, as it must be air tight, but was just curious as I know they are not designed to be actually "underwater".

 

[Wild horse 75]

What type of float is it. Hollow metal ones are less affected by fuel unless they spring a leak. Hollow plastic ones are the same. The “foam“ one all seem to eventually sink from fuel saturation. But that’s something that takes a long time. The resistor usually kicks the bucket before that happens. Obviously the best would be to never have it submerged but the float can’t pass the top of the tank and depending on the tank there may not be air space for the float to be in above the fuel. Do like DD said and just make sure it doesn’t hit the bottom of the tank when it reads empty. That’s about the best you can hope for.

 

[DirtDonk]

I don’t have any at the moment, but there are usually instructions online, from one of the tank manufacturers, showing how they recommend adjusting the float angle and arm length.
Maybe someone has a link to those?

 

[Steve83]

Modern foam floats don't sink, and won't hurt themselves or the tank if they touch bottom, which is where gauge accuracy is most-important.

(click this text)

 

[Broncobowsher]

You can also bend the arm to "tune" it. I did that to my 2010 truck that was giving me a low fuel light at a quarter tank, something that was "in spec" by the manufacturer but not to "my spec".

When you think you have it dialed in, check it with the gauge hooked up. Good chance you will be retuning it.

 

[Steve83]

I only test & tune with the gauge connected electrically. Make sure the needle's movement corresponds to the sender arm's, and that the float is at the bottom of the tank when the float arm is at the sender's lower limit.