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Testing a Gas Gauge

 
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Old 09-15-2016, 07:37 AM
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Testing a Gas Gauge

I've got a '53 F100 with 6-volt positive ground electric. My gas gauge has never worked well (only registered if I had half a tank or fuller). But since rewiring the truck, it doesn't seem to work at all. Is there a way that I can test to see if the problem lies with the gauge or the sender? Also, I recall a post that discussed how to adjust the gauges. I'll go looking for it, but maybe someone out there knows exactly where that post is.
 
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Old 09-15-2016, 08:19 AM
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Couple of things short of testing the gauge:
Did you inspect the float mechanism?
Are your grounds good?
 
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Old 09-15-2016, 07:47 PM
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I hope you didn't end up like the PO of my truck did and send full battery current into the sender. It got the card on the sender so hot it melted the card in half! Just lucky nobody was the recipient of a free trip to the moon.

Basically battery negative to the gauge (through circuit breaker and ignition switch.) From there battery positive (ground) goes through the frame to the sender unit ground wire to the sender body, the nichrome wire wrapped around the sender card and back to the gauge. Grounding the wire that goes from the gauge to the sender should make the gauge go beyond full. If no response make sure ground wire from frame to sending unit is good. Check for continuity from sender to gauge, etc.

The gauge also employs nichrome wire which is wrapped around a bi-metal leaf which bows depending on how hot it gets and causes the needle to respond. The problem lies in the fact that the bi-metal strip doesn't respond in linear fashion yet all the aftermarket sending units are wrapped that way as aftermarket gauges are linear (different technology.) You can bend the float arm, try re-meshing the gears in the gauge, install resistors, etc. but will never witness full span, accurate readings. Two ways to get full span, accurate readings: 1) locate an original sending unit ($$ when you do) or 2) re-wrap the sending unit card with progressive spacing between individual turns around the card. Why any of our list of usual vendors hasn't taken this on is beyond me, basically the same setup was used by Ford and a number of others for quite a few years.
 
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Old 09-16-2016, 07:37 AM
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Originally Posted by CBeav View Post
I hope you didn't end up like the PO of my truck did and send full battery current into the sender. It got the card on the sender so hot it melted the card in half! Just lucky nobody was the recipient of a free trip to the moon.

Basically battery negative to the gauge (through circuit breaker and ignition switch.) From there battery positive (ground) goes through the frame to the sender unit ground wire to the sender body, the nichrome wire wrapped around the sender card and back to the gauge. Grounding the wire that goes from the gauge to the sender should make the gauge go beyond full. If no response make sure ground wire from frame to sending unit is good. Check for continuity from sender to gauge, etc.

The gauge also employs nichrome wire which is wrapped around a bi-metal leaf which bows depending on how hot it gets and causes the needle to respond. The problem lies in the fact that the bi-metal strip doesn't respond in linear fashion yet all the aftermarket sending units are wrapped that way as aftermarket gauges are linear (different technology.) You can bend the float arm, try re-meshing the gears in the gauge, install resistors, etc. but will never witness full span, accurate readings. Two ways to get full span, accurate readings: 1) locate an original sending unit ($$ when you do) or 2) re-wrap the sending unit card with progressive spacing between individual turns around the card. Why any of our list of usual vendors hasn't taken this on is beyond me, basically the same setup was used by Ford and a number of others for quite a few years.
Thanks for the input. I'll be digging in to this in the next day or so. From what you write, I suspect that the reason that it doesn't register at all is related to a faulty ground.
 
 
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