View Full Version : Still more frustrated 51 commander Fuel gauge and sender

04-30-2018, 07:02 PM
OK, so I Replaced the Fuel gauge with a working unit. It was from a 52 but works fine. When I ground the sender it pegs all the way full. I purchased a new Moeller 33-240 Ohm sender and the sender checks out correctly. Combine the new sender to the gauge and it reads half full when the sender is at full. It does move between these settings. Is this a 33-240 gauge or is it like a 0-90 ohms? Is there a way to test the gauge to see the ohms it is supposed to have?

41 Frank
04-30-2018, 07:39 PM
Is your car 6 volt or has it been changed over to 12 volts? Did you purchase a sender to match the voltage of the car?

04-30-2018, 07:48 PM
It is 6volt gauge, The car is converted to 12v but has a reducer to 6volts and works. The sender was one that was recommended on the forum. I have read that the senders only read resistance. Several sites indicate that the volts do not effect the sender. It is a universal Moeller sender. I am only going on what I read and was told.

04-30-2018, 08:24 PM
The angle and length of your Sender Float "Rod" has to match the OEM Original one to read correct, it may require some bending or shortening. I am Sure that this "Moeller" ???????? Sender (why not Stewart Warner?) is not configured for a Stude. Tank depth, unless you adjusted it correctly.

Anyway, this 33 to 240 Sender IS for a 12 Volt and you were told in your "Other" String, that it DOES Matter.

Your Dash gauge is 6 Volt, so you can't bi-pass the 6-12 Converter and go with 12 Volts to match the Sender.
What you need to do also, is find out what exact Voltage that Resister is putting out, 4 or 8 probably will not work.

04-30-2018, 08:35 PM
OK, yes some said that it matters and I have read in other places that it does not matter. The recommendation of the Moeller sending unit was from this forum. I am not testing it in the tank. I have it outside the tank hooked up with a sending wire and grounded. The arm would not need to be adjusted since I can move it all the way up or down. The ohm meter confirms the correct ohms. Why does it matter? How are the senders different? Tanks inc sells senders that are universal that work either 6 or 12 volt. Is not resistance resistance? I do take much of the advise here but there are conflicting views. I assume the the gauge is OK since it does peg out when sending wire is grounded.

04-30-2018, 08:44 PM
Stewart Warner 385C-F R Swing 6-12 Fuel Level Sending Unit 240/33 Ohm (https://www.google.com/aclk?sa=l&ai=DChcSEwjyrP6BsePaAhUBXoYKHSZ3BN8YABANGgJ2dQ&sig=AOD64_2IObYTVVEG7SngFxQ8VKqoG8R3wg&ctype=5&q=&ved=0ahUKEwim_fiBsePaAhVvhOAKHYyGARYQwzwIFQ&adurl=)

Is this the unit you mentioned?

04-30-2018, 09:02 PM
Just to make sure I understand. Are you saying I can run 12volts through the gauge without frying it? The resistor/ voltage reducer is sending out 5.96 volts. I will find a 6volt sender before frying the gauge.

04-30-2018, 10:24 PM
In your particular car's case, both the gauge and the sender have to be 6 volt units, so they match each other resistance-wise. In addition, the gauge must have the voltage dropping circuit on it.

You CANNOT apply 12 volts to the six volt gauge/sender without the voltage reducer. It will burn it up.

You CANNOT mix a 6 volt gauge with a 12 volt sender, or a 12 volt gauge with a 6 volt sender. The readings will be wildly inaccurate, or they might not work at all, or they might burn up.

The polarity (positive/negative ground) of the voltage is not important, but the actual voltage (6 or 12) is. The 5.96 volts out of the reducer should do the job if it holds relatively steady at that voltage. It won't hurt anything, but the gauge may seem to wander/drift. It would be nice to see if that voltage changes when revving the engine.

If you want to keep the stock gauge in the dash, you MUST use the proper 6 volt sender in the tank and you MUST use a voltage reducer on the gauge.

If you eventually need the same knowledge about the temperature gauge/sender, the same MUSTS and CANNOTS apply.

04-30-2018, 10:45 PM
Stewart Warner 385C-F R Swing 6-12 Fuel Level Sending Unit 240/33 Ohm (https://www.google.com/aclk?sa=l&ai=DChcSEwjyrP6BsePaAhUBXoYKHSZ3BN8YABANGgJ2dQ&sig=AOD64_2IObYTVVEG7SngFxQ8VKqoG8R3wg&ctype=5&q=&ved=0ahUKEwim_fiBsePaAhVvhOAKHYyGARYQwzwIFQ&adurl=)

Is this the unit you mentioned?

I think the "6-12" notation on this part description is the adjustable length of the swing arm, not the working voltage. That "6-12" designation might be causing some confusion.

05-01-2018, 12:09 AM
/Cut/ OK, I am not testing it in the tank. I have it outside the tank hooked up with a sending wire and grounded. The arm would not need to be adjusted since I can move it all the way up or down./Cut/

Jim; most all "Universal" Sending units do have adjustable Float Arms to adjust to the Tank Depth, unless the "drop" of the Float stops about a 1/4" to 3/8" before ridding on the Tank bottom, it will not read FULL, 1/2, 3/4 and Empty correctly, that is why the length and shape of the Rod or "Arm" is so critical.

You can't just move it all the way UP and DOWN out of the Tank and call it good, because when you install it, it's range of motion will be different.


Thanks Roy for explaining again exactly what I said back in Post #4 about NOT running 12 volts to a 6 Volt Gauge. :rolleyes:

I think maybe now, Jim will get it straight and return that Wrong Sender, IF they will take an Electrical item back.

05-01-2018, 12:13 AM
Reading the product description I don't see any mention of voltage. Given that, I would assume it is 12V.

05-01-2018, 07:44 AM
I just went through the ordeal of getting the fuel gauge reading on our 54 Commander. Everything RadioRoy said is spot on. Here are a few other things I discovered along the way on my car. It may not apply to yours, but it worth a try. The 6V negative supply wire must be connected to the "ign" (lower terminal) on the gauge. The sending unit wire connects to the upper unmarked terminal. On my 54 the gauge case grounds itself through its mounting screws to the dash. You have to have a good ground to the gauge case. My gauge works as a voltage divider and would not work without a good case ground. The resistance range is 90ohms at empty and 0 ohms full. I bought a P/N: 525548 from Stephen Allens. The same P/N is listed as a replacement for all 47-55 cars. I checked and the sender resistance matches (pretty close) to the ohm values stated. The 33 to 240 ohm unit you have is for a 12V system and will not work with your 6V gauge. When you get you new 6V sender and test it out of the tank make sure you connect a good ground to the sender mounting flange before you test otherwise it will not work.

05-01-2018, 08:30 AM
So this is where I get confused. I have seen the 0-90ohms mentioned before. So which is it for this gauge it is number 526738?

05-01-2018, 09:16 AM
Your gauge is a different part number from mine. However, SI and Stephen Allens list the same sender (P/N: 525548) as a reproduction replacement for your car and mine. That sender is 0 to 90 ohms.

05-01-2018, 11:36 AM
If it's a six volt gauge, you need the 0 - 90 ohm sender. The 33 - 240 ohm sender is for 12 volt gauges only. If you can find the fuel gauge out of the cluster from a Lark, I think you may find it will physically fit in the '51 cluster, in which case you could use the 12-volt sending unit, and dispense with the voltage reducer. I seem to remember doing this once, maybe on a '54 Champion. You can swap the dial plate from the old gauge housing to the new, and carefully clip the "black light" pointer off the old gauge and cement it over the red one on the new gauge.

05-01-2018, 12:43 PM
OK, so to confirm. If I keep the 6 volt gauge with the voltage reducer I need a 6 volt 0-90ohm sender? Correct?

05-01-2018, 02:25 PM
Yes, with a 6V gauge and voltage reducer you need a 0-90 ohm sender. 90=empty, 0=full.

05-01-2018, 03:39 PM
I have been looking for the 6 volt sender. Many pop up but do not say 6 volt. I believe they are not. The SI one is $85 and I was trying to go a bit simpler than that. Has anyone purchased an aftermarket sender that works with the 6 volt?

05-01-2018, 04:44 PM
It's 90 ohms empty, and zero full. And the "zero" position really should be a bit more than zero ohms, because if you ground the sending unit wire, a properly-functioning dash gauge will peg out beyond "full" and may suffer internal damage, and you don't want that to happen. If the sending unit actually does read zero ohms at "full", I would suggest that you a ten ohm, one watt fixed resistor in series with the sending unit.

These Stewart Warner gauges are "thermo" gauges that work by using the heat evolved by resistance wire, really a tiny heating element, to cause a bimetal strip to bend, thereby deflecting the pointer. The sending unit provides the path to ground for that little heating element, so the total current through the element is controlled by the resistance of the sending unit. There is another small heating element on another bimetal strip inside the gauge, and it opposes the action of the main element. The purpose of that is to make the gauge relatively immune to changes in system voltaqe over the range expected from the car's electrical system, say roughly 5.5 to 7.5 volts in the case of a six volt car. Put 12 volts on that gauge, and the magic smoke comes out. Put a 33 - 240 ohm sending unit on a six volt gauge, and it might manage to read from empty to a quarter tank, assuming six volts to the gauge. Put a 33 - 240 ohm sending unit on a six volt gauge, and feed it 12 volts, there's a good chance both the gauge and the sending unit emit the magic smoke. And put a 0 - 90 ohm sending unit on a 12 volt dash unit, and feed it 12 volts, it will likely read from 3/4 to pegged out beyond full.

Sending units and gauges are matched to each other, and have to be kept that way. If one of the pair needs to be replaced, the replacement has to be identical to the original part.