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Mk1 Escort Smiths fuel gauge

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hak073
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2014/02/17 21:03:33 (permalink)
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Mk1 Escort Smiths fuel gauge

I've got an old Smiths fuel gauge that I bought off ebay in my mk1. One like this:

 
But its reading all wrong, indicating just under half and I run out of petrol. From what I can find in the interwebs the Smiths one uses 258 ohms empty, 90 half, 14 full. And the Mk1 sender is 73 ohms empty, 25 half, 10 full.
I also saw that you can fiddle with the calibration on the back of the fuel gauge using the little slots on the back.

 
Has anyone ever tried it? I found this site that has a bit more info on it http://www.mgb-stuff.org.uk/fuel.htm
I was thinking that maybe if I empty the tank, hook the gauge up and adjust the empty side so that the needle points to the correct spot, then stick 20L in to see if the needle is halfway, and then another 20L (40L side tank) and adjust the full side so it points to full. Does that sound like it might work?
 
I could go buy a brand new one that would work (like this one, looks like the ohm range is spot on http://www.ebay.com.au/itm/180799966779?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649 ) but that's $100 I could spend elsewhere, and I like the look of the old ones better.


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    Timw
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    Re: Mk1 Escort Smiths fuel gauge 2014/02/19 19:31:53 (permalink)
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    Basically the fuel gauge is a current reading gauge which indicates full scale on full tank - sender low ohms -
    I had one calibrated years ago at an instrument place in Sydney that no longer exists.
     
    As the current flow is reduced by the resistance of the total circuit you have to only supply a small current to the sender as it operates in a dangerous environment. You can calibrate the gauge by adding resistors in series/parallel combinations or by using a variable potentiometer but do not exceed the recommended current flow at the sender end or you will not have a car or anything surrounding it. The gauges usually have a lot of historisis  to allow for  fuel movement in the tank without wild fuel gauge movement. 
     
    BE VERY AWARE OF THE DANGER OF SUPPLYING TO MUCH CURRENT TO THE FUEL SENDER.
     
    Should be a place in Sydney that specialises in this, try a google and yellow page search.
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