Ohm range for fuel guage.
- Thread starter 41PICUP
- Start date
Flat Ernie
Senior Member
There are ways to make the aftermarket sending units work. Search "gauge" on here and you'll find dozens of hits.
41Ford1 posted: 82ohms empty & 10ohms full - don't recall if he has a 12V conversion or not.
41Ford1 posted: 82ohms empty & 10ohms full - don't recall if he has a 12V conversion or not.
41ford1
Well-known member
I am running the gauge with a Runtz 6 volt regulator on a 12 volt system.
rotorwrench
Well-known member
The little heating coil in the gauge has an Ohm value but t I'm not cetain what it is. I always test the King Seeley units with known good parts. As far as I know, all the KS indicators & senders used in the 6-volt era work with the same values.
47COE
Senior Member
As others have stated, the original King Seely sender doesn't act as a variable resistor. Current senders on the market are variable resistors, and the original gas gauge will respond to them as well.
I did some experiments with the gas gauge in my truck, and with a new replacement (resistance style) sender from Bob Drake. The results are summarized in this table.
The first column is the gauge reading: 0 is empty, 100 is full.
The second column says what resistance is needed to make the stock gauge read the value in the first column.
The third column is the resistance of the Bob Drake sender for the fuel level in the first column.
For example, a resistance of 59 ohms will make the gauge read 1/4 full. A 1/4 full tank results in the Bob Drake sender having a resistance of 36.7 ohms.
As many of us have found, the modern resistor senders tend to show full for a long time and then drop like a stone to empty. The chart shows why.
An improvement would be to add an 8.2 or 10 ohm resistor in series with the gas sender lead. With that change a full tank will show a little less than full but it will be more accurate between half and empty.
I did some experiments with the gas gauge in my truck, and with a new replacement (resistance style) sender from Bob Drake. The results are summarized in this table.
The first column is the gauge reading: 0 is empty, 100 is full.
The second column says what resistance is needed to make the stock gauge read the value in the first column.
The third column is the resistance of the Bob Drake sender for the fuel level in the first column.
For example, a resistance of 59 ohms will make the gauge read 1/4 full. A 1/4 full tank results in the Bob Drake sender having a resistance of 36.7 ohms.
As many of us have found, the modern resistor senders tend to show full for a long time and then drop like a stone to empty. The chart shows why.
An improvement would be to add an 8.2 or 10 ohm resistor in series with the gas sender lead. With that change a full tank will show a little less than full but it will be more accurate between half and empty.
41panelmark
Well-known member
As others have stated, the original King Seely sender doesn't act as a variable resistor. Current senders on the market are variable resistors, and the original gas gauge will respond to them as well.
I did some experiments with the gas gauge in my truck, and with a new replacement (resistance style) sender from Bob Drake. The results are summarized in this table.
The first column is the gauge reading: 0 is empty, 100 is full.
The second column says what resistance is needed to make the stock gauge read the value in the first column.
The third column is the resistance of the Bob Drake sender for the fuel level in the first column.
For example, a resistance of 59 ohms will make the gauge read 1/4 full. A 1/4 full tank results in the Bob Drake sender having a resistance of 36.7 ohms.
As many of us have found, the modern resistor senders tend to show full for a long time and then drop like a stone to empty. The chart shows why.
An improvement would be to add an 8.2 or 10 ohm resistor in series with the gas sender lead. With that change a full tank will show a little less than full but it will be more accurate between half and empty.
So I tried something and it worked although I don't know for sure why. My original sending unit only would show up to 1/4 and then drop. I bent the tab on one side of the unit allowing the arm to move further in that position. When I moved the arm up into the new position the gauge would go up to full. I bent the arm to adjust for up and down and the gauge seems to reflect that now. Any thoughts on why?
Flat Ernie
Senior Member
The length of the arm is crucial in the aftermarket senders. I would like to see a gauge fabricated with a shorter swing. You can play with bending the sending unit arm quite a bit to get one end of your gauge very accurate, but will typically leave you a bit off at the other end.
This is yet another reason I like to use true electronic voltage regulators instead of dropping resistors or choppers in the 12V conversions. By eliminating the variable voltage put out by the generator/alternator (12.5-15V dropped to 6.2-8.5V), you can control the rest a lot better. And, you fuel level doesn't change when you're cruising down the road and come to a stop when your RPMs drop below the cut-out level.
True electronic CVR like the L7806 are ridiculously inexpensive (~$0.10) and it baffles me why anyone wouldn't use them.
This is yet another reason I like to use true electronic voltage regulators instead of dropping resistors or choppers in the 12V conversions. By eliminating the variable voltage put out by the generator/alternator (12.5-15V dropped to 6.2-8.5V), you can control the rest a lot better. And, you fuel level doesn't change when you're cruising down the road and come to a stop when your RPMs drop below the cut-out level.
True electronic CVR like the L7806 are ridiculously inexpensive (~$0.10) and it baffles me why anyone wouldn't use them.