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Fuel gauge

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snrkld

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Hi,I am new to posting here at the forum, so I hope this does not sound to dumb.
Does anybody know the ohm range I need on my 72 midget fuel sending unit? I wish to install Auto meter gauges and this is the last gauge I need to purchase. Any help would be very appreciated.

Thanks, SNRKLD
 
Kim Webb (a.k.a. Regularman) is the Spridget gauge guy. He should be able to tell you the range.

What I've noticed is that once the voltage stabilizer was added to the BMC/BL cars the sender resistance seem to have standardized. The NOMINAL values will range from 240 Ohms = Empty to 30 Ohms = Full. If you measure one it will not match the nominal values exactly. However, I think you'll find the range I mentioned is a standard one for AutoMeter and other aftermarket gauge manufacturers.

Again, Kim can confirm if my observations are correc for a '72 Midget.
 
Are you going to pull the tank? If not then I would do this to know exacly what the range is. siphon all the gas from the tank and take an ohm reading and then fill it to the top and take another reading. I have found too often that what they are supposed to read and what they do read is very different, so you might as well check to see what you really have. Assuming you have all origninal stuff E should be about 225 and full about 20 ohms and half around 70 ohms, but I would not count on it being that close. The only way to do it right is to calibrate them both together. Also, I certainly would not count on a new one being more accurate than the old ones. From what I have seen there quality control is lacking. I had to remove windings from the last new sender I calibrated with a gauge to get it in the ball park. I am still looking for an old rotted gas tank I can cut out to get the perfect calibration setup so I can set the depth and calibrate the sender and gauge at one time.
 
Hey Kim, if you don't find a junk gas tank, how about just making a "C" shaped piece of sheet metal with a mounting surface for the sending unit. If you've got a calibrated sending unit as a starting point, you could fit it to the metal frame, then bend (or attach spacers to) the legs of the "C" to set upper and lower limits for the float travel.
 
regularman said:
I am still looking for an old rotted gas tank I can cut out to get the perfect calibration setup so I can set the depth and calibrate the sender and gauge at one time.
Click to expand...

or how about an old pickle or mayo jar from a restaurant. - total volume doesn't matter, just as long as the sender is covered.
 
Thanks guys,I have my tank out and didn't even think of measuring the ohms when full vs. empty, I will measure them tonight if I get the chance and post my results.

Thanks
 
dklawson said:
Hey Kim, if you don't find a junk gas tank, how about just making a "C" shaped piece of sheet metal with a mounting surface for the sending unit. If you've got a calibrated sending unit as a starting point, you could fit it to the metal frame, then bend (or attach spacers to) the legs of the "C" to set upper and lower limits for the float travel.
Click to expand...
It usually doesn't hit that hard limits on the sender, but hits the bottom and top of the tank with the float. I could make something like that but I would need to know the exact depth of the tank from top to bottom and I have been setting all that up in the past and it would just be easier with a real tank just cut off so just the sender area is left.
 
What I was thinking Kim was that if you have a sending unit that you have already calibrated you would use it to set the limits of the test stand you fabricate. Once you set the limits on the stand, you could lock them in place so it would simulate the inside of a real tank and you could use it to set other sending units.
 
dklawson said:
What I was thinking Kim was that if you have a sending unit that you have already calibrated you would use it to set the limits of the test stand you fabricate. Once you set the limits on the stand, you could lock them in place so it would simulate the inside of a real tank and you could use it to set other sending units.
Click to expand...
I could do that and it is sort of what I did in the past. I just had someone measure the depth of their tank at at where the sender goes in and then I used those measurements to simulate the tank bottom and top. I don't think I would trust a sender to be that accurate to set the tank limits for the next sender. Each one is a little different so its better to start out with known physical limits that won't change for the calibration and then the fuel gauges won't be 100%.
 
Ok, I measured the Ohms from my sender. I measured 24 Full and 248 Empty that was by putting it in a vise and moving the float slowly by hand until it contacted the stops. I think the readings may be slightly different with the float in gasoline as that would certainly effect the resistance between the windings and the contact.
 
The float will most probably hit the top and bottom of the tank before it hits the stops on the gauge itself though it should be close. Sounds like your sender is in the ball park. Though just because it reads right as far as travel, that float position might not be exactly right. The stiff metal wire that the float is on can be bent. If its bent up then you might read empty with 1/2 tank left and if bent down(like most are) you read 1/4 to 1/8 tank and run out of gas. I like to measure the drop to the bottom of the tank and then raise the float to a point where I think the tank would have at least a gallon in it and make it read E right there, giving a tiny bit of reserve.
 
I am going to order my fuel gauge, reinstall the sender into the tank and try to calibrate everything with the tank I plan to use.
Wish me luck
 
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