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Old 09-14-2020, 03:23 PM   #1
Made to last
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Default Gas tank sender unit.

I am baffled over how the gas tank sender unit works on my 33 Tudor. It has a supply line and a very small copper line that runs to the gauge on the dash. I do not understand the principle of how it works. There are two cups one at half full and one at full. Any help would be great.
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Old 09-14-2020, 03:54 PM   #2
petehoovie
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Default Re: Gas tank sender unit.

Does this look like the gauge you have?>






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Old 09-14-2020, 03:59 PM   #3
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Default Re: Gas tank sender unit.

No. I will post a picture when I figure out how to do it. The sender I am wondering about is mounted on top of the gas tank and the bottom goes into the gas tank. There are no floats just two cups at different levels.
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Old 09-14-2020, 04:41 PM   #4
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Default Re: Gas tank sender unit.

"The sender I am wondering about is mounted on top of the gas tank and the bottom goes into the gas tank. There are no floats just two cups at different levels."


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Old 09-14-2020, 07:28 PM   #5
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Default Re: Gas tank sender unit.

They work essentially off of air pressure (very slight at that). In fact you can test a 32-35 fuel gauge by tapping the inlet connection very fast with your thumb, and then apply pressure.
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Old 09-14-2020, 07:58 PM   #6
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Default Re: Gas tank sender unit.

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" you can test a 32-35 fuel gauge by tapping the inlet connection very fast with your thumb, and then apply pressure."

Can you elaborate on this test,please ???
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Old 09-14-2020, 09:02 PM   #7
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Default Re: Gas tank sender unit.

Quote:
Originally Posted by ford35lh View Post
" you can test a 32-35 fuel gauge by tapping the inlet connection very fast with your thumb, and then apply pressure."

Can you elaborate on this test,please ???
Hard to describe without a video, but if you tap quickly with your finger on the inlet of the fuel gauge itself and then press your finger immediately hard into the opening you will see the fluid rise. This slight increase of pressure using your finger will allow the gauge to operated presuming the gauge works..

See this thread https://fordbarn.com/forum/showthread.php?t=92481
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Old 09-14-2020, 09:30 PM   #8
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Default Re: Gas tank sender unit.

They are know as hydrostatic gauges and were used on all Fords from '32 through the '35 models. The more fuel in the tank, the more air pressure in the air and therefore a higher level of red fluid in the gauge on the instrument panel. Those little cups on the tank sending unit help maintain the pressure to avoid gauge fluctuations when cornering or going up or down hills on less than a full tank of fuel. The air line tubing on the back of the gauge on the instrument panel is very small in diameter and if it is blocked, the gauge ceases to function. If there is an air leak at the fittings on the tank unit or the gauge or in the air line itself, obviously the gauge won't function as designed.
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Old 09-14-2020, 10:01 PM   #9
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Default Re: Gas tank sender unit.

Thank's to all who have responded. Yes that picture is what I have. I will clear the small copper line to the gauge. Everything else works good. Question: Does the tank filler cap need to be a tight seal to make this sender work?
Regards
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Old 09-14-2020, 10:07 PM   #10
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Default Re: Gas tank sender unit.

Quote:
Originally Posted by Made to last View Post
Thank's to all who have responded. Yes that picture is what I have. I will clear the small copper line to the gauge. Everything else works good. Question: Does the tank filler cap need to be a tight seal to make this sender work?
Regards
No

However any leak anywhere in the system from sender to gauge will make it not work. A small pinhole in the solder on my sender stopped mine working. Once correctly set up I find mine to be surprisingly accurate .
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Old 09-14-2020, 10:33 PM   #11
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Default Re: Gas tank sender unit.

Hi Made to last, Notorious for being finicky these units are.

I'm not a '33 guy (and 35fordtn and DavidG MOST CERTAINLY are) but only the really dedicated owners that I know wrestle this beast successfully.

(Shush, but I converted my driver/beater '35 to a '36 sender and dash gauge and now I don't keep that 2 gallon can so close by.)
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Old 09-15-2020, 06:25 AM   #12
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Default Re: Gas tank sender unit.

Look the sender over VERY closely even with a magnifying glass to make sure there are no cracks in ANY solder joint especially where the tubes go through the mounting plate and where they enter the brass fittings for the fuel line and the small air pressure line.
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