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41 6volt Inaccurate fuel tank sending unit
#1380904 Thu Oct 15 2020 10:50 PM
Joined: Feb 2011
Posts: 172
W
Shop Shark
I have an aftermarket sender that won't let the gauge go to empty. The lowest ohm reading I can obtain is 3.5 ohms, any ideas how to correct this or will I need to try to find a sender that will read 0 ohms at empty. If so any ideas where to find one? Thanks in advance, Scott

Re: 41 6volt Inaccurate fuel tank sending unit
wanderinwillys #1380917 Thu Oct 15 2020 11:35 PM
Joined: Jan 2003
Posts: 308
H
Shop Shark
I bent the float arm on mine so it is correct on empty and don't worry about the full reading. I know it's full when the pump nozzle shuts off if I fill it up.


Harold Wilson
41 Chevy 3/4 Ton
Re: 41 6volt Inaccurate fuel tank sending unit
wanderinwillys #1380919 Thu Oct 15 2020 11:41 PM
Joined: Sep 2001
Posts: 30,801
ace skiver
thumbs_up


Tim
1954Advance-Design.com [1954advance-design.com]
1954 3106 Carryall Suburban [stovebolt.com] - part of the family for 49 years
1954 3104 5-window pickup w/Hydra-Matic [1954advance-design.com] - part of the family for 15 years
- If you have to stomp on your foot-pedal starter, either you, or your starter, or your engine, has a problem.
- The 216 and early 235 engines are not "splash oilers" - this is a splash oiler. [chevy.oldcarmanualproject.com]
Re: 41 6volt Inaccurate fuel tank sending unit
wanderinwillys #1380949 Fri Oct 16 2020 03:23 AM
Joined: May 2005
Posts: 7,634
B
General Purpose
The gauge has an electrical tolerance. The sender has an electrical tolerance. The gauge has a mechanical tolerance. The sender has a mechanical tolerance. The only way to do a gas gauge and sender is to calibrate them together on the bench as close as possible.

This calibration was done, explained and videoed by DADS50.


Watch out for careful drivers!!!
I'm away on an ego trip. Will be back on Feb 30.
I'm not an Auto Mechanic, but I play one on TV.
I charge $0.02 for every opinion and I take Paypal.
Plan B is always better than plan A, by definition.
You can't teach a new dog old tricks.


Re: 41 6volt Inaccurate fuel tank sending unit
wanderinwillys #1381016 Fri Oct 16 2020 02:58 PM
Joined: Feb 2011
Posts: 172
W
Shop Shark
The float is not the issue the gauge sender needs to read 0 ohms for the gauge to read empty, which is what I am trying to accomplish. I know when it's full but would like empty to be empty not almost showing a 1/4 of a tank. I could not find the tech tip for DADS50 and would like to check it out . Thanks, Scott

Re: 41 6volt Inaccurate fuel tank sending unit
wanderinwillys #1381025 Fri Oct 16 2020 04:33 PM
Joined: Mar 2019
Posts: 64
T
Wrench Fetcher
Accuracy of these fuel level systems is far from perfect, even with properly working original components.

What does your gauge read if you have the fuel sending unit out of the tank and the float in the lowest position? Make sure you ground the sending unit for this test. It does not seem right that 3.5 ohms is giving a 1/4 tank reading in a 0 to 30 ohm system.

What does the gauge read if you ground the wire coming from the gauge to the sending unit? That should represent 0 ohms and will be the lowest that the gauge will read. Try to ground the gauge very close to the gauge terminal for the sending unit connection behind the dash. Then try this test at the end of the wire at the sending unit at the tank. There could be some resistance in the connectors or that wire.

I assume that your gauge reads full if you disconnect the sending unit wire.


Rusty
Re: 41 6volt Inaccurate fuel tank sending unit
wanderinwillys #1381035 Fri Oct 16 2020 06:18 PM
Joined: Feb 2011
Posts: 172
W
Shop Shark
If I ground the wire at the sender the gauge goes all the way to empty, thus eliminating all connections and resistance from the sender. I have checked all the connections on the sender itself and gone directly to the empty side of the rheostat on the sender, the lowest reading I get is 3.5 ohms. The gauge may be a little below 1/4 but well above empty. As stated before the sender is aftermarket supposedly for this application. Obviously not of good quality. Can anyone guide me to the article from DADS50 on bench calibration of the two components?

Last edited by wanderinwillys; Fri Oct 16 2020 06:41 PM.
Re: 41 6volt Inaccurate fuel tank sending unit
wanderinwillys #1381091 Sat Oct 17 2020 12:58 AM
Joined: Mar 2019
Posts: 64
T
Wrench Fetcher
The primary variable left is to determine if the float is at the lowest limit of travel when it is installed in the tank and the resistance at the position.

What resistance does the sending unit read when it it installed in the tank and the tank is empty?

What does the gauge read when you have the sending unit out of the tank and you let the float drop as far as it can go?

I agree with the suggestion to look at the position of the wiper on the coil.


Rusty
Re: 41 6volt Inaccurate fuel tank sending unit
wanderinwillys #1381183 Sat Oct 17 2020 05:32 PM
Joined: Feb 2011
Posts: 172
W
Shop Shark
I tried all that, I went to the lowest portion of the rheostat bypassing the wiper, the rheostat where it makes connection with the wire on the sender reads 3.5 ohms and there is no change thru the riveted connections to the post where the wire connects. I am going to try a different brand and if I can't get a "0" ohm reading at empty I guess I will have to live with it. Anything above 0 ohms results in a reading above empty.. The Vendor I can't say I seem to have lost that invoice, the brand is Bob Drake, #C-9275 (It does not appear to be available on their website any longer).

Re: 41 6volt Inaccurate fuel tank sending unit
wanderinwillys #1381193 Sat Oct 17 2020 07:29 PM
Joined: May 2005
Posts: 7,634
B
General Purpose
The only Bob Drake sender for 1941 pick up is THIS. [bobdrake.com] For a Ford. 10 ohms full, 100 ohm empty. If you can't trace it back to what you bought from them, then you have NO IDEA what you have and what the specs are. You are using 0-30 ohms because you searched and found out what a real Chevy sender does. Stick with places like THIS. [classicparts.com] These are the types of Vendors we use. They sell Chevy Truck Parts only. Buy this one and you will be OK as long as your gauge is a correct 0-30 ohm compatible one. Don't use goofy companies where you can't even find what you bought on their website. Stay away from a company that has a Blue Ford Oval as their logo. They are Ford people.
This [bobdrake.com] is what you get when you search "Chevy sender". Out of stock. No mention of year. No ohmage spec. Different part number.
You will be back on track soon. Keep the faith.


Watch out for careful drivers!!!
I'm away on an ego trip. Will be back on Feb 30.
I'm not an Auto Mechanic, but I play one on TV.
I charge $0.02 for every opinion and I take Paypal.
Plan B is always better than plan A, by definition.
You can't teach a new dog old tricks.


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