Calibrating fuel gauge in antique truck

Thread Starter

Circuits123

Joined Dec 7, 2012
69
Good ideas, but when dealing with 50 year old electronics, simplicity is the best. I ended up going with a resister in parallel with the sender. It's not perfect but very close - it's accurate at Full and when the needle is at Empty there's about a gallon in the tank, which makes a nice safety margin.
 

Lyonspride

Joined Jan 6, 2014
137
Have you made sure you don't have any dodgy "earth" connections?
That would be the most likely cause of issues, it only takes a few ohms to throw a gauge measurement off.
 

ankle

Joined Dec 20, 2018
2
Hi Circuits123
Late to the conversation, but here's hoping??

I have a 59 Rover and am having similar issues, but have no idea how to read a circuit diagram etc. Would you have a picture of the final install
of the resistor in parallel that you could share?? Would be greatly appreciated

Many Thanks
 

Thread Starter

Circuits123

Joined Dec 7, 2012
69
Hi Circuits123I have a 59 Rover and am having similar issues, but have no idea how to read a circuit diagram etc. Would you have a picture of the final install
of the resistor in parallel that you could share??
I'd have to take the dash apart to get a photo. That's on my to-do list but probably not for a while. If I recall correctly, I connected the resister to the two terminals on the back of the fuel gauge. You don't need to do any soldering. If the resister has long enough wires, just wrap them around the terminals and twist the nuts back on firmly. The next time I open the dash up, I plan to put some heat-shrink tubing over the resister. Currently I just wrapped some tape around it to prevent it from short circuiting against some of the rat's nest of wiring in there.

Good luck.
 

ankle

Joined Dec 20, 2018
2
Got it!!!
Thanks so much for looking into such an old thread!!! Almost time to have her back on the road for spring, so I will try this, see how it goes,
and report findings , hopefully with a pic. Do you recall the values on the resistor?? And how did it react? Never full ? or never empty??

Many thanks Again
Ror
 

Thread Starter

Circuits123

Joined Dec 7, 2012
69
I'm afraid I don't recall about the resistor but I looked at some old comments on this thread and a couple people recommended around 300 ohms so I probably tried something like that. After adding the resistor it seems to work normally except that when it reads empty there's still a about a gallon in the tank.
 

cork_ie

Joined Oct 8, 2011
428
I'm trying to calibrate the fuel gauge in my 1970 Land Rover. When there's gas in the tank, it correctly reads full, but the needle goes down to empty too quickly while there's still plenty of gas in the tank. The gauge is made with a bimetallic strip connected to the needle. It takes 10v through the voltage stabilizer. The sender in the fuel tank is a variable resistor with a float. All the parts are new(ish) but from different vendors. When I tested the sender I get about 12 ohms when the float would be at its highest in the tank and 311 at the lowest. But when connected to the gauge, I get these results:

12 ohms = F (the needle can go higher than full but doesn't with this sender) and 9.8 volts at the back of the gauge
50 ohms = 3/4 tank
73 ohms = 1/2 tank
97 ohms = 1/4 tank
135 ohms = E
311 = < E (needle at the bottom) and 0 volts

(I couldn't test the voltage between 3/4 to E because I had to hold the sender in one hand to move the float.)

Does anyone have a suggestion of how to fix this? I suppose what I need to do is extend the range of resistance coming from the sender so it's from 12/Full to 311/Empty rather than 12/Full to 135/Empty. Or maybe do something to the gauge? My electrical knowledge is pretty limited so any basic suggestions would be welcome.
Firstly there were 5 different senders used on the series IIA, and series III landrovers ,depending on whether you had a forward or rear mounted tank and whether it was petrol or diesel and also dependent on the chassis No.You need to check you have the correct one fitted.
Assuming you do have the correct one then it sounds like a poor earth on your sender,which is no surprise with the vehicle in question.
If you have the two terminal sender with two wires Green/Black = Sender to gauge White/Green = Low fuel warning light (may not be fitted) In this case you are relying on the sender body connection to the tank and the tank mounting to chassis to get a good earth. I would advise soldering a wire directly onto the metal of the sender and connecting it to a good earth point on the chassis.
 

Thread Starter

Circuits123

Joined Dec 7, 2012
69
I don't disagree with anything cork_ie says. But I'd just add that even when you think you've purchased the "right" sender, sometimes the aftermarket versions just don't match the originals. Anyway, I finally had time to reopen my dash so I took some pictures. The resistor I used was 220ohms and I attached it between the EMPTY pole of the gas gauge and the ground. For the past year or so it's been attached with alligator clips and masking tape and it worked well but since I was there I cleaned it up, attached the resistors directly to the gauge and used some shrink tubing to protect it from shorts. Hopefully it'll work as well.

Here it is without the tubing the EMPTY end hasn't been attached yet:
IMG_1949.jpg

And after (the alligator clip in the background isn't connected to anything, I just forgot to move it before I took the photo).
IMG_1950.jpg

I also put some electrically conductive paste on each end to be safe.
 
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