Ohms Specs for Gas Gauge Senders

[Jim_Gruber]

Anyone got he resistance Specs for the 3 different type of Fuel Tank Senders Handy. I copied and saved that spec only to not be able to find it when I need it.

I'm sure my issue was a less than great ground to the tank when I dropped it a few weeks ago. Just double checking to make sure.

 

[lesingepsycho]

I don't know about the 3 types but on my 1973 Midget it's:

Fuel Sender Specs
OEM 240ohm=empty 30ohm=full

JACK

 

[Jim_Gruber]

well my 68 is the reverse of that

Reading 20 full and about 350 full

Time to make a new gasket. Hylomar is just too messy.

 

[Jim_Gruber]

OK got everything back together but still issues with gas gauge only reading 1/4 tank with a full load of fuel. I corrected what I thought was a ground issue as connection to tank was showing 5 ohms before I took everything apart. After reconnecting and cleaning everything resistance dropped to 0 Ohms.

Sender is showing 20 Ohms at empty and 350 full. Who has the correct specs for a '68 Spridget? Possibly I've got a bad sender unit.

When I had it apart before the sender got accidentally kicked when I knocked over my parts cup, but don't think any damage was done. Arm seems to more freely, but maybe still an issue there with moving completely freely when in the tank.

 

[dklawson]

Write or PM "regularman" (a.k.a. Kim Webb) on this board. He's the Spridget gauge-guy.

I'm only familiar with two ranges on BMC cars, something between 0-10 Ohms for empty to something between 70-90 full. That's for cars without the voltage stabilizer. The later cars with the voltage stabilizer had the nominal range mentioned above by Jack. You can't mix the gauge and sender types.

Kim Webb should be able to tell you what your car should have and what's going on. However, by 1968 I would expect the sending unit to match what Jack posted above.

 

[JPSmit]

Jim, mine does too - read 1/4 at empty. Someone here (and it may even have been you) said that it is because the arm is resting on the bottom of the tank and that the sender arm needs to be bent (like a toilet float I suppose) to get it to read right. Will be for me a rainy day or winter project

 

[Bob Claffie]

Not exactly appropriate to this discussion but on my vintage Vet I replaced the sender and had low readings, ie: read 5/8 when actually full! Instead of fooling around with ohm's I pulled the sender out and manually moved the arm through it's range, with everything wired up, with good results. Bending the arm (a couple times) seems to have brought it to a reasonable accuracy. Bob

 

[regularman]

The older 12v gauge had two kinds both did the 0-70 ohm range but at some point they changed what 0 ohms and 70 ohms represented on the gauge. Most likely to make it more fail safe so that if the fuel sender shorted out to ground it would read empty instead of a full tank like the old one. As for what gauge in what year british car, who knows, because these things have been mixed and matched so much.
The newer ones. 10 volt gauges. 20-30 ohms to 270-350 ohms. I'm thinking it was 20-30 for full and the 270-350 range for empty. Hmmmn, quick check. Take a siphon hose and drain all the gas out of the tank into a couple cans and see if the reading changes. Something sounds backwards. Have you removed the sender? Thing is that when the sender is pushed full against the top, sometimes there can be play in the arm at that causes it to lift the wiper off the wire wound resistor and it will read empty until you use just a thimble full of fuel and get that sender to drop a little. Still sounds like you might have a calibration issue. Mine used to show 1/8 tank when it was bone dry. I set all the ones I have done(including mine) to have 1 gallon left when its on E. You really need to calibrate the gauge and the sender together, there is to much variation in both to go by any resistance and be right.

 

[regularman]

You could rig up a 10 volt source with flashlight batteries and then hook it up like I did with this one (older 12 style) https://smg.photobucket.com/albums/v28/regularman/?action=view&current=100_1698.flv]

 

[Jim_Gruber]

Kim,

Gauge was working fine until I pulled the tank to validate that it wasn't all full of crud and the cause of my fuel pump that I replaced last year to stop working. I did need to replace a fuel pump again this year. Inside of tank is shiny and bright. Arm and float could have got jostled when I removed or reinstalled 2 x's or it could have been damaged when I kicked over accidentally the plastic cup holding the sender and screws. I put my VOM on the sender and it shows normal changes in resistance. There appears to be a factory bend in the float arm at the correct distance. All I can figure is there is some sort of resistance in there that keeps the float arm from moving to full that is not detectable to the human hand/arm. It seems to move freely.

Time to do some driving and see if it frees up and drain some gas out the fun way and reorder a new sending unit.

 

[regularman]

I the ohms from the sender look good Jim, then its got to be in the gauge. You might need to pull that one out of the dash and rig some resistors to it to see what is going on.

 

[Jim_Gruber]

Getting to the gas gauge is a total PITA. I've never been able to find a local MOWOG who can get to the thumbscrews. I've tried before believe me to get it out and clean the face of the gauge. It there was an issue with the Voltage Regulator could this be part of the problem? Not noticing any charging or performance issues otherwise. All was working fine until I pulled the sender from the tank. I think I'm going to spend $40 or so for a new sender rather than pull dash apart to remove the gas gauge.

 

[Jim_Gruber]

I pulled the Gas Tank on Bugsy yesterday to install a new Float/Sender. Latest unit from MOSS is totally different from the traditional all metal can we are familiar with. Mostly plastic, this one has been redesigned and looks like it works for multiple cars. Major difference being the length of the float arm, much shorter than the older design sender. Got everything reinstalled, gas tank gauge now goes to full again. All is well.

As I was buttoning things up I tested old sender. Seems to have full range of motion, Ohms reading are correct. I realized I may have reinstalled the old gauge when I dropped the tank so that the arm was pointed towards the pickup tube rather than away from the pickup tube. Could be that float was hanging up on the lube and could not go to full reading. May not have been an issue with sender after all, just an issue with the way the Dumb Present Owner reinstalled the float originally. My DUH!!!! Moment for the week.

Oh well, $40 for a new float / sender spent. After 3 times dropping the tank, I wasn't going to risk not having a working fuel gauge once again.

 

[dklawson]

And now it appears you have a spare sending unit for "next time". At least it wasn't too terribly expensive and you have a working gauge again.