Aux Tank Sending Unit - why did they do this?

[NJBronk]

So I’ve been troubleshooting my fuel selector gauge and went to test the ohms at the sending units. Aux tank sending unit reads 75 (empty) even though I know there’s a few gallons of fuel in it.

Question 1 - does this mean the unit itself is bad?

Question 2 - this is the first time I’m looking closely in this area - why did they cut the brace in front of the sending unit like this? Looks like an aftermarket tank (metal tabs holding the sending unit in), is the tank or sending unit the wrong size or something? Or a bad install?

I’m going to try to clean up those edges, but should I be concerned about this?

 

[gnpenning]

First, welcome.

You have been POed. (Previous ownered) I have a hard enough time explaining why I do stuff, I can't explain why others do what they do.

I'm surprised the screws don't leak unless you maybe haven't filled it yet? No kind way for me to say it other than don't trust it and redo everything. Hopefully you can get by on the main tank until you can get it fixed.

 

[billh1289]

So I’ve been troubleshooting my fuel selector gauge and went to test the ohms at the sending units. Aux tank sending unit reads 75 (empty) even though I know there’s a few gallons of fuel in it.

Question 1 - does this mean the unit itself is bad?

Question 2 - this is the first time I’m looking closely in this area - why did they cut the brace in front of the sending unit like this? Looks like an aftermarket tank (metal tabs holding the sending unit in), is the tank or sending unit the wrong size or something? Or a bad install?

I’m going to try to clean up those edges, but should I be concerned about this?

View attachment 896004

1- not necessarily. It’s pretty common that the aftermarket senders don’t read exact. Sometimes you can adjust them at the stops or by tweaking the arm. 73 ohms or so would be empty.
2- I had an aftermarket tank with that style hold down for the sender and it was always an issue. There are better options today. I’m guessing they cut that bracket in an attempt to make the install easier.

 

[NJBronk]

It definitely has fuel in it and isn’t leaking as far as I can tell.

Would fixing it mean a whole new tank?

Feels like I’m about to snowball into a 23 gallon but without leaks I may just leave it and use the main tank primarily.

 

[billh1289]

It definitely has fuel in it and isn’t leaking as far as I can tell.

Would fixing it mean a whole new tank?

Feels like I’m about to snowball into a 23 gallon but without leaks I may just leave it and use the main tank primarily.

If it doesn’t leak then I would run it assuming it’s clean and wouldn’t bother pulling the sender. Just figure out how your gauge reads- is empty 1 gallon or 5 gallons and so on. Personally I like having both tanks.

 

[NJBronk]

If it doesn’t leak then I would run it assuming it’s clean and wouldn’t bother pulling the sender. Just figure out how your gauge reads- is empty 1 gallon or 5 gallons and so on. Personally I like having both tanks.

I had put about 5 gallons in maybe 20 miles ago and it shows completely empty (75ohms and gauge at empty), so there's something up. I'm thinking I'll generally run the main tank and keep the aux as a true reserve with a couple of gallons in it treated with fuel stabilizer/ethanol treatment to get me to a gas station if needed. I don't want to open up Pandora's box right now...

Maybe in the meantime I might run the Aux dry and then put the full 7/8 gallons in just to see if it changes anything with the sending unit / gauge.

Thanks!

 

[billh1289]

I had put about 5 gallons in maybe 20 miles ago and it shows completely empty (75ohms and gauge at empty), so there's something up. I'm thinking I'll generally run the main tank and keep the aux as a true reserve with a couple of gallons in it treated with fuel stabilizer/ethanol treatment to get me to a gas station if needed. I don't want to open up Pandora's box right now...

Maybe in the meantime I might run the Aux dry and then put the full 7/8 gallons in just to see if it changes anything with the sending unit / gauge.

Thanks!

Yeah 5 gallons is more than enough in that tank you would think for it to register something. Float could be gone or have a hole in it I suppose. Did you test the wire from the sender to the gauge already? You can test wire to gauge with a jumper at the connector.

 

[NJBronk]

Yeah 5 gallons is more than enough in that tank you would think for it to register something. Float could be gone or have a hole in it I suppose. Did you test the wire from the sender to the gauge already? You can test wire to gauge with a jumper at the connector.

I didn't test the wire since the sender was giving an empty resistance reading. Not sure how to test with a jumper?

 

[billh1289]

I didn't test the wire since the sender was giving an empty resistance reading. Not sure how to test with a jumper?

Right, but good to know what works and what doesn’t. More of a “while you’re in there” approach. You can pull the rubber connector off and put a jumper between the 2 contacts.

 

[DirtDonk]

For a long time, nobody made an aux specific sender so everyone was selling rear main tax senders to work in their aux tanks. It fit, and it worked to an extent. But it probably was not very accurate.
Not sure if that would make it read empty when it was mostly full, but it would certainly have skewed the reading.

It’s possible yours has been changed since the tank has obviously been changed too.
So that’s at least one more possibility.

 

[thegreatjustino]

I'm surprised the screws don't leak unless you maybe haven't filled it yet? No kind way for me to say it other than don't trust it and redo everything. Hopefully you can get by on the main tank until you can get it fixed

Several aftermarket tank manufacturers use this style of sending unit mounting. The screws are not threaded into the plastic of the tank itself. The tank is engineered with threaded metal inserts for the screws to thread into. This is not a PO hack job, it's the style of aftermarket tank.

 

[gnpenning]

Several aftermarket tank manufacturers use this style of sending unit mounting. The screws are not threaded into the plastic of the tank itself. The tank is engineered with threaded metal inserts for the screws to thread into. This is not a PO hack job, it's the style of aftermarket tank.

Cutting the support is how they are designed to be installed?

The original retaining ring has been a problem so that might be a better option. Are the metal tabs something that comes with the tank and sender?
What seals the threads of the mounting screws?
Does the sender still have a "O" ring?

 

[thegreatjustino]

Cutting the support is how they are designed to be installed?

The original retaining ring has been a problem so that might be a better option. Are the metal tabs something that comes with the tank and sender?
What seals the threads of the mounting screws?
Does the sender still have a "O" ring?

No, cutting the support is not part of the instructions for installation. What you see on the tank for mounting the sender is 100% the aftermarket tank. Nothing fabbed or hacked by the installer or a previous owner. It was simply the design of the aftermarket tank. Why would the mounting screws need to be sealed? The tank is formed with indentations that have threaded metal inserts. Nothing about the mounting bolts, tabs, or threaded inserts touches the fuel.

 

[gnpenning]

No, cutting the support is not part of the instructions for installation.

These two statements contradict each other.

. Nothing fabbed or hacked by the installer or a previous owner.

Gotcha on the screws now. The tabs are what actually holds the sending unit in.

 

[DirtDonk]

I believe that in the second statement you quoted he was referring to the tank itself. Not the cut body pieces.
At least that’s my take on it.

 

[thegreatjustino]

I believe that in the second statement you quoted he was referring to the tank itself. Not the cut body pieces.
At least that’s my take on it.

100% correct

 

[DirtDonk]

I will say this about that though...
Even from the factory the fit was not the best. That's why using the main sending unit as an aux sending unit was problematic.
Sure, it fit the tank. But not only was it not shaped like the original inside, but the pickup tube was at an odd angle. Perhaps this is what the PO had to deal with when it was installed.

Or maybe they just got tired of the tube being so close to the body (as mentioned, even the original was) they cut it shorter to make putting new fuel line on it a little bit easier.

Paul

 

[Speedrdr]

I will say this about that though...
Even from the factory the fit was not the best. That's why using the main sending unit as an aux sending unit was problematic.
Sure, it fit the tank. But not only was it not shaped like the original inside, but the pickup tube was at an odd angle. Perhaps this is what the PO had to deal with when it was installed.

Or maybe they just got tired of the tube being so close to the body (as mentioned, even the original was) they cut it shorter to make putting new fuel line on it a little bit easier.

Paul

So, Paul, IS there a vendor that sells an Aux tank with an updated/proper sending unit? Haven’t looked for one yet, but seeing as how my aux tank has a gaping tear in the top corner, it’s getting replaced. I can’t even describe the sending unit as all that’s not rotted off is the retaining ring. Lol

Randy

 

[thegreatjustino]

So, Paul, IS there a vendor that sells an Aux tank with an updated/proper sending unit? Haven’t looked for one yet, but seeing as how my aux tank has a gaping tear in the top corner, it’s getting replaced. I can’t even describe the sending unit as all that’s not rotted off is the retaining ring. Lol

Randy

https://tomsoffroad.com/parts/66-76-ford-bronco-front-auxiliary-fuel-tank-kit

 

[Speedrdr]

https://tomsoffroad.com/parts/66-76-ford-bronco-front-auxiliary-fuel-tank-kit

Much obliged, @thegreatjustino!

Randy