Fuel Gauge and Tank Sender

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MaggieTheMoggy
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Fuel Gauge and Tank Sender

Post by MaggieTheMoggy »

Hi Everyone,

I have a 1960 (gold speedo) car with a non-working fuel gauge. Trouble is, I don't know if its the gauge itself or the sender in the tank. Can anyone point me at any info. to help with diagnosis, like what voltages should be where and/or other tips to help me find the issue.

Many thanks - Paul
graham1957
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Re: Fuel Gauge and Tank Sender

Post by graham1957 »

hello paul, with the gold type gauge you need the correct tank sender, so if you have seen your gauge work correctly you have the right one. with the speedo pulled out and looking at the rear of the gauge [right way up of course] the terminal on the right marked B is the 12volt supply , this should be live with ign on, the terminal on the left goes to earth thru the tank sender, also the gauge/speedo needs an earth wire connecting when hanging loose from the dash.now disconnect the battery under bonnet so you dont make matters worse and remove the sender wire from the gauge, measure this wire to earth and with an emtpy ish tank you should get a reading of say 2 to 20 ohms, with a full tank a reading of about 150 ohms, if no reading at all check in the boot for same reading, i have known when chassis cross member replaced some repairers just chop thru all the wires under nether and then bodge em back together so problem could be there.if still not found problem take both wires off gauge and measure the gauge resistance wise, from body of gauge to right B terminal should read about 160 ohms,from left T terminal about 100 ohms and finally accross the two terminals should be about 60 ohms. This gold face system is a moving magnet gauge and does not need a voltage stabilizer. The black face system is totally different and the parts are not interchangerble so this info would be useless for people with later cars, hope this info helps you . oh with it all connected up if you short the tank sender to earth in the boot it should give a empty reading and with it diconnected a full reading, all opposite to the later cars, Graham
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MaggieTheMoggy
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Re: Fuel Gauge and Tank Sender

Post by MaggieTheMoggy »

Hi Graham,

This is absolutely brilliant feedback - exactly what I wanted - thanks so much.

However, the one bit I didn't make clear (entirely my fault) is that I've never actually seen the fuel gauge working (or to be more accurate, it always reads full), so I'm guessing it could still be the gauge OR the sender. Is there any reading I could/should be getting from the sender, so I can pin it down to one or the other?

Thanks again - Paul
jaekl
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Re: Fuel Gauge and Tank Sender

Post by jaekl »

A quick test is to take the wire off the sender. With the ignition off, is the gauge empty? Then ground the wire, does the gauge read full. If all that works, the problem is the sender and the gauge is working properly. If it reads full even with ignition off, then it's the gauge. If grounding the wire has no effect on the gauge and still reads empty (not your case) then do the test right at the gauge, if it works now then it's a wire problem.
graham1957
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Re: Fuel Gauge and Tank Sender

Post by graham1957 »

hi paul,right with ignition on and gauge showing full, earth the tank sender wire in the boot if the gauge comes down it is the tank sender thats stuck or open circuit. if no change pull speedo out and earth its case and then earth the Tterminal this should cause needle to point to empty if not it looks like the gauge is faulty but this can be confirmed by the res reading in my last text, Graham
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graham1957
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Re: Fuel Gauge and Tank Sender

Post by graham1957 »

what jaekl says is correct for the black face speedo/fuel gauge but not for the gold one. The gold face one is a moving iron gauge, the black face one is a hot wire gauge and uses a stabilizer [not voltage stabilizer] as it switches on and off the voltage to the gauge to regulate the temp of the hot wire in the gauge by altering the mark space ratio in relation to the supply volts which is not as steady as you may think, on a moggy it can be between 11 and 15 volts, but dont you worry as yours is the early moving iron gauge, good luck with it, im off now for a walk and to play with my ball, Mackie the border Collie
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MaggieTheMoggy
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Re: Fuel Gauge and Tank Sender

Post by MaggieTheMoggy »

Dear Mackie The Border Collie,

Made the very big mistake of showing your post to my wife, who loved the picture and then started (not for the first time) making noises about always wanting a border collie and it would be good for me to get out walking etc etc... Big mistake.

Anyway, because of your (again) very helpful advice, I at least managed to walk as far as far as the garage and started the suggested tests. Now I thought (and put in an earlier post) that the gauge was always reading full, but when I looked again, it wasn't, it was reading empty, so I took your advice , disconnected the tank sender and earthed the wire back to the gauge. The gauge jumped to full and stayed there. I disconnected the earth wire and it still stayed at full, which puzzled me.

I started the engine (to do something else) and the gauge went back to zero, but not smoothly, in perhaps 3 or 4 'jerks'. I repeated the earthing/de-earthing of the sender wire and it the jerky behavior of the gauge was quite repeatable.

So my diagnosis is this: its the tank sender that is faulty and I need a new one, but also that the gauge magnet(s) are 'sticky' and/or not moving smoothly for some reason. Does that make sense? Any suggestions from anyone as to how I can 'unstick' the gauge and make it move smoothly again after I've replaced the sender?

Many thanks everyone and Mackie/Graham1957 in particular.

Paul
IslipMinor
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Re: Fuel Gauge and Tank Sender

Post by IslipMinor »

Paul,

The 'gold' gauge head in the speedo has a very light spring that returns the needle to 'Empty' when the tank is genuinely empty, or the ignition is turned off or a fault with the wiring /tank sender.

Is the needle catching on the gauge face? It should swing with no resistance and with either the ignition 'off' or no connection to the sender, the magnets play no part in an 'Empty' reading, that is controlled by the spring. The more fuel in the tank, the less electrical resistance in the sender, so more current/magnetic force that opposes the closing force of the spring, and a higher reading on the gauge.
Richard


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