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Grounding Fuel Tank Sending Unit '55 Olds S88

Grounding Fuel Tank Sending Unit '55 Olds S88

Old June 7th, 2017, 04:54 AM
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Question Grounding Fuel Tank Sending Unit '55 Olds S88

Im going to be getting a 55 Olds Super 88 in a week or two and have been told the gas guage doesnt work because the owner had replaced the fuel tank sending unit, but forgot to run a ground wire from the sending unit to the chassis.

Any advice on the easiest way to do this? I dont have a lift in my garage so this sounds like it may be a real pain, or near impossible.
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Old June 7th, 2017, 06:19 AM
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If the previous owner didn't install a ground wire then you will have to drop the tank and install one on the fuel sending unit. Use a wire brush and clean the frame thoroughly where you attach the ground. Once you reinstall the fuel tank attach the ground to the frame and you should be golden.

Before doing any of this check under the car to see if there might be a ground wire that is just disconnected. Maybe the current owner is mistaken.
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Old June 7th, 2017, 07:02 AM
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Thanks Olds64. Just a couple dumb questions here - I assume I need to drain the gas (apparently the 55 has a drain plug), and disconnect the fuel lines, unless you know a shortcut or know that there is enough slack/length in the fuel lines and sending unit wiring to just unstrap the tank and lower it to the ground?

I dont have a lift, so it would come down only a couple feet.

Thanks!
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Old June 7th, 2017, 07:15 AM
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Sorry, I just gave a quick overview.

1) Lift the rear end of the car with a floor jack and secure it with safety stands under the frame.
2) Drain as much fuel as you can out of the tank with either a hand pump or the drain plug.
3) Disconnect the fuel lines at the tank.
4) Put a floor jack under the tank so it is supported when you remove the straps.
5) Loosen the straps holding the tank in the car.
6) Lower the tank with the floor jack.
7) Remove the 12V wire from the fuel sending unit.
8) Remove the fuel tank from beneath the car.
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Old June 7th, 2017, 08:11 AM
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The original ground is attached to the fuel line with a clamp ( not the best idea Old's has had) but many of us drill and tap a small hole on the frame close by and attach it there.

If you are lucky and the ground wire is there but not attached I would do the drill and tap method as the clamp method has a tendency to corrode and give poor or no readings. Also if a repair to the gas line is needed (spliced with a rubber hose as a connector) it won't upset the ground.

Good advise from Olds64 on the removal. If you can run most of the gas out of the car before you undo that gas plug you will be better off, it can be a mess trying to get a pan big enough and low enough to catch all the gas left in the tank... Tedd.
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Old June 7th, 2017, 09:02 PM
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If that drain plug has never been removed, it may be REALLY tight. Pumping out the fuel before loosening the straps may be best. It may also be best because remember if you do get the plug loose you will have to get it tight again so it doesn't leak.
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Old June 7th, 2017, 09:29 PM
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If you just want to test it you could take a test lead with an alligator clip on each end and hook one end to the tank and the other to the frame and see if the gauge works them. The sending unit has to grounded to the tank with the screws that attach it.
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Old June 8th, 2017, 09:36 AM
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Originally Posted by redoldsman View Post
If you just want to test it you could take a test lead with an alligator clip on each end and hook one end to the tank and the other to the frame and see if the gauge works them. The sending unit has to grounded to the tank with the screws that attach it.
If that works, could I just leave it that way for awhile or is there a spark/explosion hazard?
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Old June 8th, 2017, 10:48 AM
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Originally Posted by setzman View Post
If that works, could I just leave it that way for awhile or is there a spark/explosion hazard?
You could leave it that way without worrying about an explosion or fire; however, the alligator clip would probably fall off the moment you drove down the road.
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Old June 8th, 2017, 11:01 AM
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Originally Posted by Olds64 View Post
You could leave it that way without worrying about an explosion or fire; however, the alligator clip would probably fall off the moment you drove down the road.
Thank you - one more dumb question....is there a recommended guage wire for this ground? I figure I would just use 16 guage since the book shows that the lead wire is a 16 guage size.
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Old June 8th, 2017, 11:17 AM
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16 gauge wire would be fine. More important than the gauge of the wire (as long as you don't use 22 or 00 gauge) is the quality of the terminal ends. Do you know how to solder? If not, get help from a friend who can. You want to ensure you use heat shrink on each of the terminal ends.
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Old September 13th, 2017, 10:27 PM
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Why do s it seem that most people don't come back with the outcome or type of fix it took?
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Old January 29th, 2018, 05:21 PM
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Job done

I ran a ground wire from the sending unit to the frame and that seems to have done the trick well, but with the tank completely empty, the guage reads 1/8 tank. Is there a calibratiion I can do?
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Old January 29th, 2018, 09:01 PM
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Originally Posted by setzman View Post
I ran a ground wire from the sending unit to the frame and that seems to have done the trick well, but with the tank completely empty, the guage reads 1/8 tank. Is there a calibratiion I can do?
If everything is working properly, you should be able to cure it by bending the float arm and/or the "stop" on the sender. With the tank in its normal position it should show "E"; with it inverted, it should show "F".

Another problem with these cars is that they will "run out" of fuel with about 3 gallons remaining in the tank. This is due to the tip of the fuel pickup being above the bottom of the tank. See attached figure. To cure it the tip of the pickup must be extended. I extended mine by using a "sock" from my 70s Ford pickup truck. Those strainers have a tube extension built into the strainer which effectively lowers the tip.
Attached Images
File Type: jpg
DSCN2901.JPG (2.36 MB, 2 views)

Last edited by Ozzie; January 29th, 2018 at 09:05 PM.
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Old January 30th, 2018, 04:22 AM
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Great advice

Thanks Ozzie. You are exactly right. My car was idling in my garage last week and it ran out of gas, and I was surprised when I drained the tank that there was like 3 gallons still in it. I thought it would run on that much gas, so I started worrying that the car stopped running for some other reason.

Thanks for the advice on the sender. Honestly, I dont know if I want to pull that tank down again being as busy as I am, so I may just call 1/4 tank as Empty going forward until something forces me to do it
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Old January 30th, 2018, 06:20 AM
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Originally Posted by Ozzie View Post
This is due to the tip of the fuel pickup being above the bottom of the tank. See attached figure. To cure it the tip of the pickup must be extended. I extended mine by using a "sock" from my 70s Ford pickup truck. Those strainers have a tube extension built into the strainer which effectively lowers the tip.
That's a handy diagram. Has the fuel sock from the Ford truck worked well for you? I ask because Ford trucks are notroious for loosing the sock off the end of the fuel sending unit. My 86 f250 will run out of fuel with 4 gallons still in the tank.
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Old January 30th, 2018, 06:41 AM
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Originally Posted by setzman View Post
Thanks Ozzie. You are exactly right. My car was idling in my garage last week and it ran out of gas, and I was surprised when I drained the tank that there was like 3 gallons still in it. I thought it would run on that much gas, so I started worrying that the car stopped running for some other reason.

Thanks for the advice on the sender. Honestly, I dont know if I want to pull that tank down again being as busy as I am, so I may just call 1/4 tank as Empty going forward until something forces me to do it
That's O.K. as long as you remember that you can't count on running on much of that last 1/4 of the tank. Some guys have ended up stranded when they thought they had some fuel left.
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Old January 30th, 2018, 06:49 AM
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Originally Posted by Olds64 View Post
That's a handy diagram. Has the fuel sock from the Ford truck worked well for you? I ask because Ford trucks are notroious for loosing the sock off the end of the fuel sending unit. My 86 f250 will run out of fuel with 4 gallons still in the tank.
So far, so good. My pickup is a '76 F-250. That one has a 3/8" line, but some have a 5/16" line. The strainers come in both sizes. When I did the tank refurbishing on the truck I found that the strainer had disintegrated except for the inner extension piece. So after 40+ years it was still draining the tank completely, but not doing any straining.
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Old January 31st, 2018, 12:02 PM
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Originally Posted by Ozzie View Post
That's O.K. as long as you remember that you can't count on running on much of that last 1/4 of the tank. Some guys have ended up stranded when they thought they had some fuel left.
My father taught me to fill up when you get down to 1/2 tank (especially in winter for extra weight over the drive wheels). Id count 1/2 as my empty.
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Old January 31st, 2018, 12:47 PM
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Originally Posted by Fitti Fi View Post
My father taught me to fill up when you get down to 1/2 tank (especially in winter for extra weight over the drive wheels). Id count 1/2 as my empty.
X2 on that.
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Old January 31st, 2018, 02:56 PM
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Originally Posted by Fitti Fi View Post
My father taught me to fill up when you get down to 1/2 tank (especially in winter for extra weight over the drive wheels). I’d count 1/2 as my empty.
Originally Posted by ignachuck View Post
X2 on that.
This advice sounds nice in principle, but in reality, who drives their collector cars on snow and ice-covered winter roads? It seems most people in northern climates put their cars in storage for the winter or at most take them out only on sunny, dry days.

Modern cars are mostly front-drive now, so filling the tank would actually take weight off the drive wheels. Trucks, of course, are a different story.
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Old January 31st, 2018, 03:39 PM
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Originally Posted by jaunty75 View Post
This advice sounds nice in principle, but in reality, who drives their collector cars on snow and ice-covered winter roads? It seems most people in northern climates put their cars in storage for the winter or at most take them out only on sunny, dry days.

Modern cars are mostly front-drive now, so filling the tank would actually take weight off the drive wheels. Trucks, of course, are a different story.
I don't know about that, I had my car for 12 years running on the top half of the tank before I ventured into the bottom half and ran out of gas somewhere in nowhere Montana.I didn't know that it would run out at a 1/8 tank. I'm very much more educated now..... Tedd
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Old January 31st, 2018, 03:46 PM
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Originally Posted by Tedd Thompson View Post
I don't know about that
You don't know about what?

You're confusing two different things here. The two posts I quoted are talking about keeping their tanks full to improve traction in the winter time. You're talking about keeping your tank full because your gas gauge becomes inaccurate when the tank gets close to empty. Those are two different situations, and I argued that keeping your tank full to improve traction is largely irrelevant to most old car people because they don't drive their old cars in winter weather. It's irrelevant to modern car people (but not trucks) because most modern cars are front-drive.
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Old February 1st, 2018, 06:00 AM
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I remember driving my dad's 76 98 20 years ago during the winter with studded snow tires on the back. That was in KCMO so the weather wasn't horrible. We did throw some sandbags in the trunk to give it more traction.

Whenever I drive my 86 f250 I put 4 or 5 gallons in it every day. 1-1.5 gallons in the front take and 3-4.5 gallons in the rear tank. I want to drop the front tank, restore it and fix the fuel sending unit so it's pretty much at 1/2 empty right now. The rear tank I keep full because I use it on the highway between home and work.

Last edited by Olds64; February 1st, 2018 at 06:03 AM. Reason: Ooops...
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Old August 9th, 2018, 07:46 AM
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In the end, I attached a ground wire to the screw on the sender and attached that to the frame. I didnt find that the ground wire did much. The reason it was pegged on F was the lead to the sender wasnt tightened down, so the circuit was basically open.

I was able to adjust the sender with a little screw on it and got it to read almost E. Here are pics at completely empty (tank drained) and exactly 10 gallons of gas in it. Im calling success on this! Thank You!
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File Type: jpg
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Old August 9th, 2018, 09:00 AM
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Glad you fixed your problem.
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Old August 9th, 2018, 09:38 AM
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Originally Posted by setzman View Post
In the end, I attached a ground wire to the screw on the sender and attached that to the frame. I didnt find that the ground wire did much. The reason it was pegged on F was the lead to the sender wasnt tightened down, so the circuit was basically open.
I think the bottom line here is that you had an open circuit. It just wasn't due to a bad ground. Your sending unit apparently grounds through the sending unit housing rather than through a separate wire like the more modern ones. But at least you got it working.


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