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TR2/3/3A TR3 Fuel Gauge Again.....Adjusting?

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karls59tr

Obi Wan
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Well I found out why my fuel gauge never registered.....the float was full of gas Doh! when the tank is full now the gauge shows more than half full but still not accurate. What is the correct method of adjusting the gauge and the float to give an accurate reading?
 
Is there a way to test the float while it is out before installing .
 
There is a way to test while the gauge is out. Will probably take someone like Randall to explain it...but had help with mine while the float was out. I did change the float while the tank was in the fixed position later...no fun...but can be done. Gil NoCal
 
There is a good article on calibrating the type of fuel gauge used on TR3 at
https://www.mgaguru.com/mgtech/electric/fg_10.htm

The resistance values given are not quite right for a TR, so measure your sender first and adjust accordingly.

For a hollow metal float like the TR3 used, one way to test is to dunk it in a pan of hot water and watch for bubbles. If there is a leak, air will come out as the water warms the air (and hence increases pressure inside). To double-check, after removing the float and waiting for it to cool, shake it. If you can feel liquid inside, it's bad.

But I'm not sure offhand what kind of float your TR6 & TR7 would have, Don. Also, your gauges work differently, so Barney's article is not applicable.
 
TR3driver said:
...But I'm not sure offhand what kind of float your TR6 & TR7 would have, Don. Also, your gauges work differently, so Barney's article is not applicable.
Click to expand...

Just wondering for the 6. If I install the float back in.
Will try the hot water trick
 
karls59tr said:
Well I found out why my fuel gauge never registered.....the float was full of gas Doh! when the tank is full now the gauge shows more than half full but still not accurate. What is the correct method of adjusting the gauge and the float to give an accurate reading?
Click to expand...

Did you repair the float, or did you buy a new sending unit?? I bought a new fuel sending unit from Moss, and couldn't get the gauge to register properly.

This link explains it all...
 
Aloha Karl,

Here is a link on how to calibrate a fuel gauge.

https://mgaguru.com/mgtech/electric/fg_06.htm

If you don't want to build the the box you can use a combination of resistors to simulate the input from the sending unit. That is discussed in FG102e later on in the link. I built the calibration box a few years ago for about $20 with bits from Radio Shack.

As Randall pointed out the TR fuel sending unit has a different resistance than the MG unit. It is about 90 ohms, so you need to use 22 and 47 ohm resistors. One 33 ohms resistor is 1/4 on the gauge, two 22 ohm resistors in series or one 47 ohm resistor for 1/2, three 22 ohm resistors in series or a 47 ohm and a 22 ohm resistor in series for 3/4 and two 47 ohm or four 22 ohm resistors in series for full.
 
<span style="font-size: 10pt"><span style="color: #003300">The ideal adjustment would be to have your gauge be accurate at full and empty. The range on the Smiths FT 3331/02 is 89-91 ohms full and 3-6 ohms empty. That being said, even if your float is OK (or fixed, or replaced) there are other problems with the 50+ year old Smiths unit. Corrosion on internal parts which can't be accessed to clean up is the biggest culprit.. The best way to go is the unit sold by NOS. They come with an implied warranty and are within a few ohms of being a match to the Smiths unit.
I've been repairing and calibrating the Jaeger FG 2530/20 fuel gauge (TR2-3B) for quite some time. Rather than fool with various resistors I just use a 2-200 ohm potentiometer. The actual calibration is accomplished by moving the 2 internal coils in the gauge to match the resistance output of the sending unit at a given point. In order to move the coils, it is necessary to loosen the two 7/32" nuts on the back of the gauge so the coils can be slid either closer or further from the pointer (needle) Again the fact that the gauge is 50+ years old, getting those coils to move can be a problem. The two coils are connected by a single wire about the size of a human hair. If you break that connection, your gauge is down for a repair job, and it's REAL easy to break.
Frank </span>[color:#003300]</span>
 
Just jumping into the fray here.
On my 6 sending unit when I hook up the meter I don't get a fluid rising and fall of the OHMS. lots of dead spots and then it will read.
Is this normal?
 
DNK said:
Just jumping into the fray here.
On my 6 sending unit when I hook up the meter I don't get a fluid rising and fall of the OHMS. lots of dead spots and then it will read.
Is this normal?
Click to expand...
Pretty normal I'd say, for a worn-out sender.

But you should replace it if you want your fuel gauge to actually work.

:troll:
 
Gee I wish I saw this thread yesterday... Ran out of gas this morning with a 1/4 tank registering on the gauge. Thank goodness Glen was in front of me in his TR3. He sipped home and returned with some petrol. I should have known that I need fuel even thou the gauge was off. I will try adjusting the gauge sometime next week, or just put fuel in when I know that it is getting low....
 
Or carry an old fashioned wooden yardstick behind the seats.
 
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