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Forward Look NON-Technical Discussions -> 1955-1961 Forward Look MoPar General Discussion	Message format

'57ADV

Posted 2015-02-03 1:19 PM (#469304)
Subject: '57 DeSot Adventurer - Faulty Sender or Fuel gauge?

Regular

Posts: 89

Having some problems with my fuel gauge. It reads half full when in fact it's empty - I know this because I ran out of fuel! It reads nearly full with just as few gallons in the tank. I've taken the sender unit out (it is a new tank and a new (repro) sender unit. If I short the sender wire to earth the gauge reads "Full". So I began to suspect the sender unit being incorrectly calibrated. Rigging the sender unit up outside of the tank but connected to the gauge and sure enough when the sender's on it's lower "stop" pin, the gauge reads half full. If I gently raise the float my gauge rises to the "full" mark well before the sender unit float hits its stop pin. (about three quarters of the travel I'd guess). Next I measured the ohm resistance of the sender unit. With the float level at the empty position I get a reading of 73.3 ohms. At the full position it reads 7.8 ohms. I've Googled these results and it seems they should be between 10 and 78 ohms for MOPARS of this year. I spoke to a reliable supplier of repro sender units and he confirmed the same resistance numbers for 50's MOPARS but wasn't sure which was empty and which was full. He did say though that my readings were within 10% so would be considered within tolerance. Anyone got any ideas where to go next? Seems pointless buying another sender, I'm loathed to remove the dash gauge unless I have to, perhaps it's an earthing problem or my vehicle wiring but I'm not sure how to test this? Any help really appreciated! Thanks Mark

57chizler

Posted 2015-02-03 2:08 PM (#469306 - in reply to #469304)
Subject: RE: '57 DeSot Adventurer - Faulty Sender or Fuel gauge?

Expert

Posts: 3778
2000

Location: NorCal

10 ohms is Empty, 73 ohms is Full. A quick test for the gauge is to ground the sender wire and turn on the key, the needle should climb to full...shut off the key as soon as the needle tops out.

ronbo97

Posted 2015-02-03 3:29 PM (#469308 - in reply to #469306)
Subject: RE: '57 DeSot Adventurer - Faulty Sender or Fuel gauge?

Expert

Posts: 4043
2000

Location: Connecticut

Do you have the original sending unit ? If so, you can use that one as a reference.

Ron

'57ADV

Posted 2015-02-04 4:12 AM (#469333 - in reply to #469306)
Subject: RE: '57 DeSot Adventurer - Faulty Sender or Fuel gauge?

Regular

Posts: 89

Hi thanks. that's weird because my sender is reading 72.3 ohms empty and 7.8 ohms full? As I take the float up towards the "full" stop point the gauge needle climbs towards full but reaches full way before the float on the sender reaches it's stop. At the other end as I bring the float down towards it's "empty" stop point my gauge reads half full and will not go below this reading even when the float reaches its maximum downward travel. From your note it seems my gauge and the sender are the wrong way around if 10 ohms is empty?

I tried the test you suggested and the gauge needle climbed to full as soon as the sender wire was grounded.

'57ADV

Posted 2015-02-04 4:16 AM (#469334 - in reply to #469308)
Subject: RE: '57 DeSot Adventurer - Faulty Sender or Fuel gauge?

Regular

Posts: 89

Hi Ron, sadly I don't have the original sender I can just see that both it and the tank are brand new and fitted by the selling dealer. Having tested the resistance of my sender it seems to be within the normal and correct range - although 57Chizler suggested the ohm readings on my sender are reversed? This is weird - I'm usually ok with electrics but this one has me puzzled. I did notice that when the gauge is reading half full and you try to start the car the energy used to turn the starter motor seem to result in the fuel gauge dropping to zero - so I'm now wondering if there is a supply problem to the gauge?

Thanks for your help, cheers Mark

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