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'41 fuel gauge


valk
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Greetings Boys, hope all are staying out of harm's way. 

Thought I'd look into my faulty fuel gauge and wondered if anyone knew of a clever way to determine if the problem is in the gauge or the sending unit before I take the tank down.  And, no, I don't have the neat tool referenced in the manual that does just that. The needle moves from below empty when the ignition is off to just above empty when the ignition is on but is stuck there regardless of the amount of gas in the tank. The manual also suggests the problem is the sending unit when the gauge is stuck on full. As mine is stuck on empty, I guess this doesn't apply. 

Thanks for any help,

Peter

'41 Roadmaster 

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My gauge does the same thing and it's on my list of things to repair sooner rather than later. I think our mutual friend Neil tackled his not too long ago and used a fresh sending unit to cure his problem.

 

Here's a great article by '41 Buick expert Bill Anderson that gives some pretty helpful quick diagnostics for vintage fuel gauges (which all work pretty much the same way):

 

https://www.oldcarsweekly.com/restoration/fueled-frustration-fixing-faulty-fuel-gauges

 

Gauge Reads Empty At All Times

If the fuel gauge reads empty at all times, the probable causes are:

• The wire between the sender and gauge is shorted to ground.

• The sending unit is shorted internally.

• The float has a hole and no longer floats.

To determine what is causing the problem:

• Remove the wire from the contact stud on the sender. If the gauge now reads full, the sender is faulty.

• Disconnect the wire from sender terminal at the dash gauge. If the gauge now reads full, the wire between the sender and gauge is shorted to ground.

 

 

Edited by Matt Harwood (see edit history)
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Thanks Matt, great info and I’ll let you know how it works out.

Pains me to hear of your business troubles. I know lots of folks are having  similar experiences, not that that helps at all. Hang in there man.

peter 

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Matt has a good memory.  My gauge had the opposite problem -- it was stuck on full.  So the diagnostic procedure was different.   Grounding the wire from the gauge to the sending unit resulted in the gauge going to empty.  This showed that the problem was with the sending unit, and the replacement sender I got from Bob's cured the problem.

 

For Peter's problem (as Bill Anderson explains), the diagnosis requires disconnecting the wire from the gauge to the sender.  I can tell you that removing the wire at the gauge end is a royal PITA.  There is very little room to work under the dash as far as getting access to the back of the gauges.  I had my panel out when I put in a new wiring harness, but without removing the panel I can tell you it will be very difficult.

 

At the sender end, however, you get a break.  Normally, you would have to go ahead and drop the tank in order to get access to the sender to disconnect the wire from the gauge unit.  But there is a bayonet-style connector in this line that you should be able to get access to in the trunk without too much difficulty.  At least on the sedan, the wire from the sender enters the trunk through a hole in the trunk floor on the driver's side.  The connector should be about a foot farther along the wire, which is tucked up under the trunk liner where it gets bundled with the tail light wires.  I assume the coupe is the same.  Disengage the bayonet connector, and you should get your answer whether the problem is in the gauge or not.

 

Neil

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This is great stuff. I suspect the wire is  grounded somewhere between the gauge and sending unit so I’ll disconnect it at the tank. Per Anderson, if it still reads empty that at least points to a bogus wire if I’m reading it right and I won’t have to pull the tank
 

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I'm hoping for your sake that it goes to full when you disconnect the wire.  That will mean dropping the tank and replacing the sending unit, but I actually think that will be less work than finding where the wire is grounding or, even worse, having to replace the gauge.   And it would give you a chance to see what the inside of the tank looks like and have it sandblasted and coated if need be.  Good luck and keep us posted.

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Thanks Neil. I agree that would be the best/easiest outcome. Regrettably, in this instance, my trunk is beautifully carpeted in the wrong material and is glued down on all surfaces (ugh). I may be able to pry the trunk side "cover" on the driver's side off enough to see if I can disconnect the wire from down in there but if not, I'm screwed. I'm talking prematurely but I think I'm headed toward having to drop the tank and replace the whole wire unless I can find an obvious ground somewhere. Question: could I then just cut the existing wire as close to the gauge as possible and splice in the new one as opposed to disconnecting it at the gauge itself? It's cheating but wouldn't bother me. 

buicktrunk2.jpg

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Wow, your trunk looks like a comfortable place to crawl in take a nap! 😄

 

If I were you, I would definitely try to pry up the carpet in the left rear trunk floor and see what you can find.  I can't remember for sure, but I think that if you look underneath, you will be able to see the wire coming from the sending unit where it comes out on top of the tank and goes through a hole in the trunk floor.  That would help you to locate exactly where you need to pry the carpet up.  In fact, I'll go down and take a peek at my car right now.  Nothing else to do these days!  I'll be right back.

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Yes, here are a few pics.  You can see from underneath where the wire comes over the top of the tank and goes through the hole into the trunk.  On my car there are two wires because I ran a dedicated ground to the sending unit when I put in the new one.  On your car, you should see a single wire in the same spot, more or less.  There should be a rubber grommet around that hole, but I didn't bother finding one to put on mine when I put the new wires in.  But this raises a thought in my mind -- it's a long shot, but if the grommet is also missing on your car and the wire got chaffed from rubbing against the bare metal, this might be a place where it's grounding out.

 

gauge_wire.thumb.jpg.8ecc72fba9c872c5eb5a9727e7c00a98.jpg

 

1976696359_gauge_wire(2).thumb.jpg.aca148933c2fb8ab1aa953a307b6d4d3.jpg

Edited by neil morse (see edit history)
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You're very welcome, of course.

 

And to answer your other question, yes, there's no reason why you couldn't "cheat" in the way you suggest if you run a new wire.  It would be much easier to splice a new wire in at the gauge end, and it doesn't need to be super close to the gauge where you do it.  The original wire from the gauge goes to the six-pin connector up near the parking brake handle that joins the front harness to the rear harness.  On the other side of the connector, the wires go up the A-pillar and under the headliner and then back to the trunk.  But you obviously don't need to do that if you end up running a new wire.  Just drill a hole from the trunk and run the wire under the carpet, up into the area behind the kick panel, and then splice it onto the old wire somewhere between the gauge and the six-pin connector.

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The float has a hole and no longer floats.

 

I just removed the sending unit from two 1940 tanks and the float was cork in both of them.  The cork had become very brittle and split upon the slightest touch.  At that, the tank would always read empty.

 

Great list Matt, I've spoke to Bill Anderson a time or two in the past, he does seem to be an excellent resource.

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Looks like kgreen is correct, i have a bogus sending unit.  Either the float is bad or internals. I located the sender-to-gauge wire going through the trunk floor that Keith referenced (mine goes into the trunk at the rear driver side corner near the exhaust) and the previous owner thankfully installed a bullet plug there in unheated shrink wrap.  Disconnected the plug and, sure enough, the gauge went to full. So I have to pull the tank after all but don't have to mess with any wires. Decent trade off to me. The only fly in the ointment is I also have to remove yet another splash pan to lower the tank but it appears easy enough. 

Thanks Boys, I''ll wrap this up and report back when I install a new sending unit. 

buickfuelgaugewire.jpg

buickfuelgauge.jpg

buicktrunkshroud.jpg

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That's great news, but I think you meant to say "Neil" and not "Keith."  (I know that Keith and I have similar avatars, posed in front of a maroon '41 wearing a fedora!)  😄

 

As I said, that was the outcome I was hoping you would have since replacing the sending unit is much easier than dealing with a broken gauge or a grounded wire.  If you look on my thread, you will find my description of dropping the tank -- it turned out to be much easier than I thought it would be.

 

Neil

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Dang Neil, just reviewed your fuel tank experience - thanks for paving the way! So well documented that I feel even I can do this. The plank-and-lift technique alone will save me time and embarresment. 

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Dropped the tank today and sure enough the float was full of gas. I was hoping I could just replace the float but the unit arm did not move as freely as it should so I'll replace the whole unit. I did not remove the tank entirely, just lowered it, because doing so would have been a major PITA as the tank filler pipe fouled my exhaust pipe and I would have had to really work it to get it out. Everything is pretty clean back there anyway so there wasn't a need. Any preference regarding the float: cork vs metal?? I may not have a choice but I thought I'd ask. 

Peter

buicksending unit.jpg

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Hi Peter:

 

Great work!  This is the sender I got from Bob's, which will work for your car since I see that you have a rubber hose connection to the fuel line like I do.

 

https://bobsautomobilia.com/fuel-system/gas-tank-sender-1936-56-fs-368/

 

It has a metal float.  The one I replaced (which I assume was the original) had a cork float.  I just went with what Bob had, and it has been working fine.

 

On my car, the filler pipe just dropped down without hitting the exhaust so it was easy to fully remove the tank.  Given your situation, I can understand why you didn't remove it altogether, but it would be nice to get a peek inside and see what kind of shape it's in.  Did you lower it enough so you could get your cell phone camera in position to take a shot through the hole for the sender?  That's what I did (easy with the tank fully removed, of course), and I found a lot of rust on the inside of the tank as you know from the pics I posted on my thread.  I'm just thinking that it might be worth your while to wrestle with that filler pipe if the inside of the tank looks as nasty as mine did.

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Thanks Neil, you were a big help. Your point is well taken - I’ll take a pic or two tomorrow of the inside. I’d done this a couple times before on my 1950 Packard coupe I had 45 years ago! 

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Ok the tank took some wrestling but I managed to get it out. Getting it back in probably won't be as easy.  The good news is that it has been sealed by Renu (pic) and it is clean inside. The curious news is that it is covered in a rubber-like material so painting it would be a challenge - what kind of paint would stick to that?  It also has an extra vent line drilled into the side of the filler tube, but that might be a good thing. Doesn't hurt anything anyway. I'm not about to strip all the rubber goop off the tank so I'll re-install it as is and win the ugly but functional gas tank award. The spots on the top are from it not being totally dry after cleaning (I'm not known for my patience).  Ordered the sending unit - who knows when it will arrive. 

buicktank1.jpg

buicktank3.jpg

buicktank2.jpg

buicktank.jpg

buicktank4.jpg

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Gas Tank Renu is good, don't mess with the coating--it'll void the lifetime guarantee. It's ugly but at least that's one thing you don't have to worry about and it's largely hidden under the car.

 

I wonder if that extra fitting was for some kind of return line? I haven't seen it on cars as late as ours, but early cars fitted with electric fuel pumps often use return lines to keep from overwhelming the primitive carburetor floats designed to run on little more than gravity. The 1930 Marmon we currently have in inventory has both a mechanical pump as well as an electric pump with a return line plumbed into the filler neck of the gas tank. Whenever the electric pump is running, there's a trickle of gas going back into the tank. I suppose it's a way of skipping a regulator. But like I said, our cars don't seem to mind 5-7 PSI from a standard electric pump. 

 

What else could it be?

 

 

Edited by Matt Harwood (see edit history)
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I'm sure your right, the car has both a mechanical and an electric pump. The line I disconnected from the filler neck is routed where I can't really see where it ultimately goes but it is headed toward the electric pump. 

Unrelated to this topic, the car has another "add-on" feature I just noticed.  Tough to see, but the differential has a vent installed -  the vent line (pic) follows the brake line above the diff and ends "open" on the other side. The previous owner apparently knew all the tricks in the trade. 

buickdifferential.jpg

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Regarding the painting, I think they were not painted from the factory.  The "vent" on the filler tube is an added fitting for sure. I did the same on mine for the electric pump return from the fuel injection.

 

  Do your self a favor. When installing the new sender connect a 12G wire to on of the mounting screws and ground to the frame somewhere. Can't have too much ground.

 

 

 

  Ben

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New sending unit came today and is now installed. Fuel gauge works great so case closed. 

I got it from CARS, INC as opposed to Bob's for 2 reasons: 1) the old one I had was from Bob's but developed 2 crippling problems - a cracked float that filled with gas, and the float arm did not move freely up and down but got seriousy stuck. Either issue would render the gauge useless, and 2) Bob's minimum purchase policy and exhorbitant shipping charges just rub me the wrong way. 

The gauges are a bit different - both have good and bad charactoristics that I believe are a wash.  Thanks all for your help.

Peter

buickrear.jpg

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