Fuel Sending Unit Question for '65

[kdml]

I am replacing the fuel sending unit in my '65.  Although, my previous sending unit was new it only worked properly intermittently.  I bench tested the new sending unit and it worked perfectly (0 ohms empty, 90 ohms full).  

 

I am slowly adding fuel to the tank, one gallon at a time, and checking the fuel gauge and sending unit reading to ensure all is working properly.  I am up to 4 gallons and the fuel gauge hasn't moved and the sending unit is still reading 0 ohms.  I looked into the tank and can see that the float lever has not even moved off the lower stop.  

 

Am I supposed to be bending the float lever to get the gauge to read right or does the tank hold 4 gallons before the gauge begins to register?  I have included a picture of the old sending unit which is identical to the new sending unit.  The float sits above the fuel sock which makes sense to me.  If I need to bend the float lever I will need to bend it around the fuel sock as it sits right over the fuel sock.  I have also included a picture inside the tank and a closeup showing the float level sitting on the lower stop after 4 gallons were added to the tank.  Any thoughts on what I need to adjust to get a reading?

 

Thanks

Doug

  

 

[rocketraider]

I think by that time GM fuel gage design had changed so that when the fuel gage read E there were still 3-5 gallons in the tank. If no reading by the time there are 6-7 gallons in it you may need to regroup.

[Bloo]

On any of these GM gauges that use 0 for empty alignment is critical. There is no way to "adjust" the gauge electrically.

 

Floats shouldn't bang the top or the bottom, but the sock should be as low as possible. Don't forget you wont be able to suck 100% of gas from the tank, so some of that excess fuel capacity is just lost, and there's nothing you can do about it. You can use a hand powered transfer pump to check. Don't use anything electric. Put enough gas in to bring the sender up a tiny bit, as read with an ohmmeter. Suck fuel out through the pickup (wiggling the tank so that you are sure the sender is responding) until the sender is back down to the "0 ohms" or very close that it measures when on the stop. Now change the container you are pumping into, and pump fuel out until you suck air and can't get any more fuel. The fuel in this second container is the true size of your reserve. The shop manual may tell you. Sometimes they did. Rocketraider's numbers sound right to me.

 

 

[kdml]

Thanks.  3-5 gallons before the gauge reads.  That's about 1/4 tank of gas.

 

Did a little more testing today.  I bent the float lever to make it parallel with the pickup to get the gauge to read sooner (see first picture).  Looks like I start getting a reading now between 3-4 gallons.  However, when I flip the tank over and check the resistance I only get 73ohms.  I looked inside the tank and noticed the float hits the top of the tank (see second picture) before I get a full 90ohms.  I even got close and can see the float lever doesn't sit on the top stop before the float hits the top of the tank (see circle in third picture).  

 

I am starting to wonder whether I have a correct gas tank.  It fits well and looks like an original tank, but have no idea what has happened over the years.  Is there a way to determine an original tank?  Is there a part number somewhere?  Or do I just need to continue to modify the sender to work?

 

Thanks

[Bloo]

I think you will have to keep screwing with it until it behaves. Sock as low as possible, float does not hit the bottom or the top, can swing 0-90 (or a wee bit more) between stops, still some "reserve" gas between the point where the sender hits 0 ohms and the point where you can no longer suck gas through the pickup.

 

Anything left in the bottom is just lost capacity. I wonder If GM rated the tank in the actual volume, or in the volume the customer would see between having the tank completely full and running out of gas? Someone probably knows, but I must admit I have never paid much attention to that.

 

I personally marvel at the fact GM stuck with this design as long as they did. In another thread, someone who actually worked at AC told me the sending units were set up at AC (on a jig I think) and that it was not a problem in production, at all. I believe him, he was there. Nevertheless, I still think decades later with reproduction parts, used parts, shelfworn parts, parts that have been sent through the mail, etc., you had better check everything or you are going to be taking the tank out a whole bunch of times. My own experience bears that out. The design of the system leaves no room for error.

 

I highly recommend adding a ground wire to the sending unit. It helps prevent problems down the road.

 

 

Edited January 23, 2022 by Bloo (see edit history)

[XframeFX]

Seems most concerns are addressed. Agree with what's said especially a ground wire.

I dealt with this on my '63 last summer. It took many trial fits. Thinking my repro sender/pickup was meant for a repro tank. (Being 1963, has a 45 ohm sender not 33)

 

I commented on my install here:

https://forums.aaca.org/topic/366695-1963-project/page/5/#comments

"If you plan to replace the Pickup/Sender (it's the old 33 ohm type), install the new sender with the screws NOT tightened down. Then check the function by flipping the tank over with a multi-meter or wire it to the fuel gauge.

I had to do this several times. It seemed that the float arm was too long, meant for a repro tank? My tank was not damaged so not sure why I had to mess with the sender. Doing several bends on the float arm got it to do the full sweep.

The manual says to allow for a couple of gallons of reserve at "E". No-Can-Do, at E, I am on fumes!

Use FI hoses and clamps when re-assembling and a ground wire."

[RivNut]

On my 64, the gauge will about 1/8 full when it's empty. Gota learn the peculiarities for each individual car.  

 

My two daughters shared a little Toyota SR5 in which the fuel gauge was broken.  They never ran out of gas. Every time they got gas they had to 'fill er up;" no nickle and diming it.  Then they had to reset the trip odometer to 0. I told them that they could neve let the trip odometer get to 200 miles or they'd run out of gas.  They never figured out that at 200 miles, they had about 5 gallons or another 120 to 130 miles left in the tank.  Worked like a charm.

[60FlatTop]

Mine reads 1/4 tank at empty. Been like that since I got the car in 1978. I was a problem twice but that was a long time ago.

[telriv]

I got Turbinaters to work exactly as it should by bending the float arm/float to rest on the bottom of the tank.

When new my '64 Riv. would run out of fuel at 1/4 tank, but that also depended on how much weight I had in the trunk.

 

Tom T.

[rocketraider]

I had a Ford pickup years ago that if the gage said 1/4 tank you had best be looking for a gas pump. Also a 60 Chevy with the old style gage that E meant E. Sold that car to a friend and was headed to the local country store one night to shoot pool and found Jeff, his kid brother and the Chevy on the side of the road, out of gas. The skinny grinning boy learned something that day.

 

The best was my mother's 69 Impala. She didn't trust the gage, was completely paranoid about running out of gas and would back it up to the farm tractor gas tank and fill it every couple days.

 

Keep in mind she drove the car 10 miles a day, so with the Impala's 24 gallon tank she should have easily been able to drive a month on a tank of gas.

 

My dad started grumbling about how much of his farm gas she was using and told me to fill the car up and record the mileage, then told her not to put any gas in it till she'd driven a couple weeks.

 

3 weeks later I took the car to fill it up. She had driven 156 miles and it took a shade over 5 gallons to fill it- meaning that Chevy 350 was averaging over 30mpg.

 

I took the car back and my dad said there was no way, that 15 was believable but not 30. Mama set her lip and said "I put some in it because I was afraid it would run out."

 

My dad locked the tractor tank after that🙃.

[kdml]

Thanks all.  Looks like I am not the only one with this issue.  

 

With the adjustment I made to the float lever, the pickup tube should still be covered in gas when the gauge reads empty.  If I have to choose between being accurate about being empty or full, probably safer to be accurate about empty.   

 

I only need about a little more adjustment to get the float to swing completely through it's arc.  I may try to adjust the pickup tube to move it closer to the bottom of the tank.  There's some room to lower it.  Then I can lower the float a little more and still have the pickup tube completely submerged.

 

Thanks 

[kegart]

I would prefer a little reserve when it reads empty.  I had a '65 Riviera  40 years ago and when it read empty you were empty. 

 

Kevin 

Edited January 23, 2022 by kegart (see edit history)

[XframeFX]

I remember back-in-the-day a friend being annoyed that his mid 70s Impala wouldn't go far on a fill-up where the fuel tank was flattened somewhat tearing down gravel roads up in the Yukon.

He had it repaired and we picked it up the next day. He asked the mechanic how he accomplished such a quick turn-around out in the middle of nowhere. He was told a cigarette butt on the end of a long stick directed at one of the openings of the stripped tank out in the middle of the lot - - BOOM! 

[rocketraider]

Expedient expansion!🤓

[steelman]

40 plus years ago when I bought my 55 Chevy hardtop, the gauge always read full. I had filled it up down the street from where I bought it, so knew I had a few days. Hot 350 so I expected 7 mpg, but really didn’t care. Ran several days on full. Then, it started bobbing between F and E, back and forth, back and forth. If it stopped bobbing, you had better be within sight of a gas station, because you were out out and coasting.

[XframeFX]

On 1/24/2022 at 5:54 AM, steelman said:

40 plus years ago when I bought my 55 Chevy hardtop

I wanted a '55 Chevy 2 hardtop since I was twelve. By the time I acquired my driver's license in 1973, they were all rusted-out and gone where I lived in the putty capital of north america!

I didn't want anything high dollar or nice, just something to kick around town in.

I hate to count, but that was 49 years ago!

[1965rivgs]

  The first gen cars were notorious for running out of fuel at 1/8th on the gauge. I experienced this myself several times when purchasing a "new to me" Riv and has been confirmed through many member`s related experiences.

  If I had to choose I would rather err on the full reading as opposed to empty. Probably a good idea not to pick up fuel from the very bottom of the tank too.

Tom Mooney

[Bloo]

2 hours ago, 1965rivgs said:

  The first gen cars were notorious for running out of fuel at 1/8th on the gauge. I experienced this myself several times when purchasing a "new to me" Riv and has been confirmed through many member`s related experiences.

  If I had to choose I would rather err on the full reading as opposed to empty. Probably a good idea not to pick up fuel from the very bottom of the tank too.

Tom Mooney

 

That is a non-negotiable design issue of the fuel gauge. The trouble is they used 0 ohms for the "Empty" point. There is always a little resistance, even when new. A tiny bit of degradation in the wire, sender, or ground means that the needle can never reach "E".

 

 

Edited January 26, 2022 by Bloo (see edit history)

[jframe]

I went thru all this a few years back when I first got mine. Put in a new sender, and it would show 3/4 full when I filled the tank. After me and a tech at work put the car on a lift and removed the tank about five times chasing it, I finally took a chance and bent the arm down using the SWAG method, and must have hit the sweet spot. Now, when it's full, it's almost dead on F, and it seems fairly accurate; half a tank takes around 10-11 gallons to fill up. It was just a lot of trial and error, and luckily the shop had a pump to drain gas tanks.

[telriv]

ALL save yourselves some time & aggravation.  From where the sender mounts to the tank, with the gasket in place, measure down to the bottom of the tank. IF I remember correctly it is 5".  So with the float bottomed out it should be on the very bottom of the tank. Now raise it up 5" & it should be somewhere close to the top of the tank.  

I've had to take some units & actually bend an "S" in the link to make it shorter to get the results I was looking for. Some of the links are longer than others. 

This is the price we have to pay with this reproduction JUNK  that's available to us today which drives us ALL crazy including those of us in the business of repairing vehicles.

Again, just my thoughts on the subject.

 

Tom T.

[crowvet]

Has anyone ever successfully reached through the filler neck and been able to bend the arm down? I can see mine looking in it. I replaced mine a year ago and only read 3/4 when full.

 

[EmTee]

Maybe use something like this to grab, then push...?

 

https://www.amazon.com/X-Long-Flex-Cable-Pick-Up-4-Finger-Retriever/dp/B006ZEOXJY/ref=asc_df_B006ZEOXJY/?tag=hyprod-20&linkCode=df0&hvadid=312003160272&hvpos=&hvnetw=g&hvrand=17449562915071153825&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=1023225&hvtargid=pla-569776745433&psc=1

 

[kdml]

Made more progress this week on adjusting the sending unit. 

 

I made a slight adjustment to the pickup tube so the fuel sock is at the bottom of the tank.  I then adjusted the float lever.  There are actually three places you need to adjust the lever (see picture).  Adjust at bend 1 to make the bend closer to a 90 degree angle.  This pulls the float in tighter to the sending unit when full, so it won't hit the top of the tank too early.  Then adjust bend 2 until the float is in line with the top of the pickup tube.  You don't want the float below the top of pickup tube, as the pickup tube will be sucking air prior to the gauge showing empty.  Finally, make sure the float is actually level in relation to the mounting of the sending unit.  Mine was not level and would not hit the top of the tank flat.  

 

With these adjustments the gauge begins to register with 3 gallons of gas, which is also when the pickup tube becomes completely covered in fuel.  I added one gallon at a time and checked the resistance of the sending unit and gauge level and found the gauge was fairly accurate.  It's about 1 gallon off.  At 6 gallons it reads 1/4 tank; at 11 gallons it reads 1/2 a tank and at 16 gallons it reads 3/4 tank.  By the time I hit 20 gallons, I am at full.

 

Hope this helps people in the future

Doug