Gas gauge problem

[martin53]

I finally got a stock gas tank for my 53 Coronet but the gas gauge stays at full and flickers. The system is switched to 12v. Do I need a reducer for the gas gauge.

[dpollo]

you need to reduce the voltage to 5.5 to 7  between the ignition switch and the gauge.   You may have cooked the sender already but it is more likely that there is a problem therein.

 

If you have a test lamp... the type with the needle pointed probe, fasten that between the body and the wire which attaches to the sender.  Turn on the ignition and the gauge should register on the low end of its scale  maybe 1/3.

[Andydodge]

My 1940 Dodge with a 318 Poly and 12 volt system running the stock gauges has a voltage drop resistor, same as an ignition resistor on the power side to the fuel gauge and it works reasonably well, ie, when the tanks full it reads full, when it reads low I refill it.........lol............andyd  

[ptwothree]

Don't know why everyone installs resistors when going to 12v.  Resistors change value with heat and cold and as resistance goes up over time in the circuit.

 

What you need is #7806 voltage regulator. Mount one on a heat sink.  One side gets battery 12v, other side is 6v to the gauge.  This device will input a constant 6v to the gauge and will help stabilize a shaky needle.  Only cost $2/3 bucks.  A lot of factory gauges needed a constant 5v supply.  Therefore a #7805 would work there.  Electric temp gauges work well with these regulators. 

[chrysler1941]

9 hours ago, ptwothree said:

Don't know why everyone installs resistors when going to 12v.  Resistors change value with heat and cold and as resistance goes up over time in the circuit.

 

What you need is #7806 voltage regulator. Mount one on a heat sink.  One side gets battery 12v, other side is 6v to the gauge.  This device will input a constant 6v to the gauge and will help stabilize a shaky needle.  Only cost $2/3 bucks.  A lot of factory gauges needed a constant 5v supply.  Therefore a #7805 would work there.  Electric temp gauges work well with these regulators. 

100 %

I too never understood the crude resistor usage.

Edited August 26, 2019 by chrysler1941

[Los_Control]

Let me jump in and ask a question. I am just going by what "Tanks" told me when I ordered my new tank and sending unit.

And this may only apply to single wire sending units?

Or are they wrong?

 

I told them I was staying 6 volt positive ground, and needed a sending unit to work with that for the new tank.

 

They told me, My gauge does not care about the voltage, and the sending unit would work with either 6 or 12 volts.

 

So I gather, we are sending power to the gauge, which does not care if 6 or 12 volts, and the sending unit sends a signal to the other side of the gauge.

 

If this is true, why do we hook a resistor or a voltage reg in the system at all?

I just assume, Tanks inc. is in business selling these products, I assume they know what they are talking about.

[chrysler1941]

6 minutes ago, Los_Control said:

Let me jump in and ask a question. I am just going by what "Tanks" told me when I ordered my new tank and sending unit.

And this may only apply to single wire sending units?

Or are they wrong?

 

I told them I was staying 6 volt positive ground, and needed a sending unit to work with that for the new tank.

 

They told me, My gauge does not care about the voltage, and the sending unit would work with either 6 or 12 volts.

 

So I gather, we are sending power to the gauge, which does not care if 6 or 12 volts, and the sending unit sends a signal to the other side of the gauge.

 

If this is true, why do we hook a resistor or a voltage reg in the system at all?

I just assume, Tanks inc. is in business selling these products, I assume they know what they are talking about.

 

I was commenting on voltage reducing but if you want an answer on voltage, I need to know if you have a one or two wire sender.

[Los_Control]

1 minute ago, chrysler1941 said:

Let me jump in and ask a question. I am just going by what "Tanks" told me when I ordered my new tank and sending unit.

And this may only apply to single wire sending units?

I do have single wire sending unit on my truck, and I know some newer cars have 2 wire sending units ... thus my question.

 

Is it the gage that needs reduced, or is it 2 wire sending units that need reduced?

[chrysler1941]

Just now, Los_Control said:

I do have single wire sending unit on my truck, and I know some newer cars have 2 wire sending units ... thus my question.

 

Is it the gage that needs reduced, or is it 2 wire sending units that need reduced?

It's the gauge. It works on double electromagnets system. Do you want a more detailed explanation? I have it described somewhere

[Los_Control]

1 minute ago, chrysler1941 said:

It's the gauge. It works on double electromagnets system. Do you want a more detailed explanation? I have it described somewhere

No but thanks, I was just wondering if there really was a difference in the gages, I do not have that system ... but wondered if the voltage reducer really was needed.

 

I only questioned because am told a single wire system it is not needed,  I think I now know with a 2 wire system it is needed.

Sorry for interrupting the thread and thank you for your clarification.

[chrysler1941]

13 minutes ago, Los_Control said:

No but thanks, I was just wondering if there really was a difference in the gages, I do not have that system ... but wondered if the voltage reducer really was needed.

 

I only questioned because am told a single wire system it is not needed,  I think I now know with a 2 wire system it is needed.

Sorry for interrupting the thread and thank you for your clarification.

 

Just want to clarify that your gauge need 6 volts to work properly regardless of one or two wire system. 

It's all about ohms law and resistor of the sender. 

You can use 12 volts but you need a sender with higher Ohm value.

Edited August 26, 2019 by chrysler1941

[Los_Control]

2 minutes ago, chrysler1941 said:

 

Just want to clarify that your gauge need 6 volts to work properly regardless of one or two wire system. 

It's all about ohms law and resistor of the sender.

This is why I am asking .... Tanks inc told me over the phone, that it did not matter.

Maybe the lady confused me, maybe what she really meant was .... The sending unit does not care?

She was pretty animate about not worry about 6 or 12 volt, it just did not matter on these old fuel gauge systems.

I told her over the phone, I may switch to 12 volt in the future.

[Richard Cope]

Since you have already converted to 12 volt, may want to consider what I did.  For my 39 Ply. buying gauges and sending units on e bay was expensive that may or may not work.   I sent a non-working gas gauge to D&M Restoration, Jack indicated that he could attach the face plate to a Ford gauge, that worked on 0 - 90 ohm.  Fortunately I had a 0-90 ohm Isbro sending unit, and when I put a new tank on connected the Ford gauge w/ Ply. face to the new tank and sending unit.  Works great and is one wire.  I believe he said the price differs depending on the gauge.  I went a little more, since had the gauge cluster out sent the other gauges and had the faces reprinted.  D&M did a quality job. 

 

Rich

[Adam H P15 D30]

This is all you need.  Been using one for years and my gas gauge works perfectly. 

https://www.speedwaymotors.com/Speedway-Runtz-12-Volt-to-6-Volt-Voltage-Reducer,2374.html

I've also seen where the gauge doesn't care and where someone spliced in a light bulb.  Most gauges probably don't care

 

Adam

[Andydodge]

Some have wondered why I used a resistor on the fuel gauge.........well considering that all this was done by me in 1973........45 years ago, maybe I can be forgiven considering I was 19 and was going by what the local sparky was advising me.............lol.............and its working o/k still........lol.......maybe the new fangled things wer'nt around then.........lol.........andyd

[ptwothree]

What if your battery voltage is more then 6v.  Would the gauge be accurate?  How about if the resistance value in the sender changed.  Would the gauge be accurate?  The gauge needs to see whatever voltage it is designed to operate on.  My point was, that a regulator provides a rock solid voltage for that it needs to be accurate.  Resistors can and will change value for many reasons and will have an effect on how the gauge functions.  Weather the system came with a regulator, my '64 Rambler had a 5v points type regulator from the factory, to our 6v MOPARS with no regulators at all, both benefit with a constant voltage source.

 

In the case of my AMC, the gas and temp gauges went crazy when the stock regulator was failing.  A 7805 solid state reg put everything right.  Resistors have there place, but not if a working and accurate gauge is important.  BTW....these parts are a couple of bucks, put out little heat and take very little space.

[YukonJack]

4 hours ago, Adam H P15 D30 said:

This is all you need.  Been using one for years and my gas gauge works perfectly. 

https://www.speedwaymotors.com/Speedway-Runtz-12-Volt-to-6-Volt-Voltage-Reducer,2374.html

I've also seen where the gauge doesn't care and where someone spliced in a light bulb.  Most gauges probably don't care

 

Adam

When I converted my 47 Plymouth to 12 volts I used a Runtz Resister. My gas gauge worked for 2 days and quit, the Runtz went bad. I removed it and have been running 12 volts to my gauge for many years now without any problems.

[Adam H P15 D30]

Im sure there’s a bad one every once in a while. 

Edited August 27, 2019 by Adam H P15 D30

[chrysler1941]

18 hours ago, YukonJack said:

When I converted my 47 Plymouth to 12 volts I used a Runtz Resister. My gas gauge worked for 2 days and quit, the Runtz went bad. I removed it and have been running 12 volts to my gauge for many years now without any problems.

 

Again another crude resistor. 1,5 Ohms is almost a short circuit. Drawing 4 Amps and 25 W which means a lot of heat.  

Much smarter with a regulator as suggested above, fixed linear DC For example

 https://www.ebay.com/itm/DC12V-To-6V-DC-Buck-Power-Converter-2A-12W-Step-Down-Voltage-Adapter-GOOD-ur/183897828588?hash=item2ad12a2cec:g:kKgAAOSwfSldORaR

[Adam H P15 D30]

Drove my 49 for 2 hours yesterday, Runtz resistor was not hot but whatever..

You could also grab a 60's-80's Ford IVR.

Edited August 27, 2019 by Adam H P15 D30