Fuel Sender Resistance

[marko]

Here is a little question for you all....in relation to a TR3A

 

Does anyone know the 'resistance' of the fuel gauge sender unit at both empty & full (in Ohms) if it needs to be re-calibrated...

 

Your help is most appreciated....

 

Thanks Mark

Edited May 4, 2010 by marko

[david ferry]

Mark,

 

I don't know the answer to your question, although I do have a number of later senders.

 

There are two different sidescreen fuel gauges that have different senders, although they look the same. Somewhere I have notes on which sender goes with which gauge. They are not interchangeable. Interestingly (or otherwise) there is only one repro sidescreen sender gauge which seemingly doesn't work properly with either gauge!

 

It is possible to adjust the max and min settings on the gauge although if you decide to do this, be careful as it's easy to break the gauge when trying to do this. I've never tried.

 

What I would do is send the sender, and gauge that it is to be used with, to a gauge restorer who should be able to make sure that the gauge reads accurately at each end of its deflection. Accuracy anywhere in between is somewhat difficult to achieve and is of course far less important than an accurate empty (or somewhere close) reading.

 

If needs be, I can find some senders to meter out and let you know the resistance at max and min. You'll need to let me have the part number of your sender to make sure mine are the same as yours.

 

David

[marko]

Thanks David - appreciate your help

 

I have sent the original gauge off to JDO Instruments for a refurb / re-calibrate and he has asked specifically for the 'resistance' of the sender @ both empty & full, according to his notes it should be approx 70/80 ohms @ full & 0/5 ohms @ empty but best not to assume anything, so therfore was looking for clarification from someone that has already done this.

 

I have ordered a new sender from Moss (part no 203610)

[david ferry]

Mark,

 

Unless the original sender is not working, the new one from Moss will not help you. The new one will not work properly with the gauge.

 

The ones I have are all original.

 

If you let me have the part number of your sender, I'll check mine to see if I can help you.

 

David

[marko]

Gentlemen

 

Just to update you the sender unit I have from Moss - it is 3 ohms at empty and 95 ohms on full.

 

The fuel gauge will be calibrated accordingly.

 

David thanks for your offer of assistance - very helpful as usual

 

Cheers Mark

[jbenajes]

The web site www.mgaguru.com (about MGAs, incidentally) has an excellent series of articles on the fuel gage (with internal mechanism and circuit shared apparently by MGAs and TR3s).

 

If we are to trust these guys, the sender resistance is linear with the tank level: Full is 68 ohm and empty zero ohm, and of course half is 34 ohm.

 

Jesus

 

 

[John Soffe]

The web site www.mgaguru.com (about MGAs, incidentally) has an excellent series of articles on the fuel gage (with internal mechanism and circuit shared apparently by MGAs and TR3s).

 

If we are to trust these guys, the sender resistance is linear with the tank level: Full is 68 ohm and empty zero ohm, and of course half is 34 ohm.

 

Jesus

 

 

Hi, I have just removed my sender - to cure a small leak - and mine is original and has the following No. FT3331/02. Made by Smiths Motor Accessories and also has, at right angles to the above number MM2. I get 3ohms at empty and 78ohms at full.

 

John

[marko]

Thanks John...

[Paul Down]

Mark,

 

I have a spare 3A sender type: FT3331/06

 

it measures 1.5 Ohms min , 80 Ohms max

 

These guages are not precision instruments so I would have thought figures within a reasonable tolerance should be OK.

Edited May 5, 2010 by Paul Down

[marko]

Thanks Paul

 

I'll let you know how I get on with the Moss one I ordered once the Fuel Gauge comes back from the Instrument repairer / calibrator...

[mike fleet]

Thanks Paul

 

I'll let you know how I get on with the Moss one I ordered once the Fuel Gauge comes back from the Instrument repairer / calibrator...

 

Check the length of the Moss sender .I tried 3 senders from moss manners and anotherthey are all from the same manufacture and are about75mm shorter than the original,so empty reading when half full

Mike Fleet

[tthomson]

The web site www.mgaguru.com (about MGAs, incidentally) has an excellent series of articles on the fuel gage (with internal mechanism and circuit shared apparently by MGAs and TR3s).

 

If we are to trust these guys, the sender resistance is linear with the tank level: Full is 68 ohm and empty zero ohm, and of course half is 34 ohm.

 

Jesus

 

 

 

 

Hi Jesus,

 

The sender might have a linear resistance, but the gauge does not provide a linear reading. Moving iron or hot wire meters are inherently non-linear.

 

TT

[Guest ntc]

Do any of you gents still have an original for sale? the moss ones do not work right

[Guest ntc]

So can you fit a voltage stabiliser ? Tony

[david ferry]

Neil,

 

No.

 

The gauges work in a totally different way to later gauges that do need a voltage stabiliser to give correct readings.

 

David

[Guest ntc]

Neil,

 

No.

 

The gauges work in a totally different way to later gauges that do need a voltage stabiliser to give correct readings.

 

David

 

 

Pooh just crasping at straws ,

 

Thanks David

[Icarus60]

The resistance of mine is zero empty and zero full! Whilst isolating the non reading on the gauge i found that the float of the sender unit was very convieniently positioned directly under the filler cap such that I could hook the sender with a piece of stiff wire and pull it up to the full position. Fixing the fuel sender is now on my to do list. This hook method might be useful for calibration.

[Mychael]

I was not aware of the different senders and only found out too late. My car had a working fuel gauge but not correct for a 3A, I think it was a gauge from a 4 or something else.

I located an original gauge and had it proffessionaly overhauled but it will not work with the existing sender.

 

Next time I will give both the sender and the guage to the instrument guys to service and match and calibrate.

[tthomson]

I know its, a little late to add another entry here, but the sender units are very simple and could be repaired using some suitable resistance wire, a bit of soldering and a good clean. In most cases, the slider starts to get grubby and makes bad contact with the resistance wire. This increases the apparent resistance making the sender give erroneous readings. Fisr step is always to clean them especially the slider contact.

 

 

 

TT

[Philippe_TR3a]

From my own experience, a bad grounding of the tank itself was the cause of the bad functioning of my gauge.

[Guest ntc]

Update it took 3 from Moss to get one that had an acceptable range 10 out of 10 to them they kept sending one,the gauge was sent to JDO and works spot on

Edited November 6, 2010 by ntc