fuel level sender Penta, 1989 vintage.

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petrolhead63

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I have a fuel level sender broken on one tank. I wonder if anybody has looked at one?
I have drilled the brass rivets and taken the float/stick out of a tube and found the float stuck and a long thin wire detached from one of the two top terminals.
I can't understand how the float alters the resistance with this wire to alter the reading.
I think the wire runs down to the bottom of the slider and back to the other terminal and if this is the case is may be repairable.
The float has two little guides the wire would seem to run through.
I could dismantle the one out the other tan but risk having two broken ones!
Previous senders seen involve a typical variable resistance coil with a float altering the windings in the circuit.
 
petrolhead63 said:
I have a fuel level sender broken on one tank. I wonder if anybody has looked at one?
I have drilled the brass rivets and taken the float/stick out of a tube and found the float stuck and a long thin wire detached from one of the two top terminals.
I can't understand how the float alters the resistance with this wire to alter the reading.
I think the wire runs down to the bottom of the slider and back to the other terminal and if this is the case is may be repairable.
The float has two little guides the wire would seem to run through.
I could dismantle the one out the other tan but risk having two broken ones!
Previous senders seen involve a typical variable resistance coil with a float altering the windings in the circuit.
Click to expand...

Made by VDO
 
The contacts on the float short out the resistance wire so when float is high the wire is mostly shorted out and the gauge will read high. When the float is low very little is shorted out so resistance is high and gauge reads low.
Perhaps it can cleaned and reassembled. I think ASAP supplies may sell them.
 
Last edited:
Montemar said:
The contacts on the float short out the resistance wire so when float is high the wire is mostly shorted out and the gauge will read high. When the float is low very little is shorted out so resistance is high and gauge reads low.
Perhaps it can cleaned and reassembled. I think ASAP supplies may sell them.
Click to expand...

thanks, I came to that conclusion but at the moment the float with the little guides for wires all looks plastic to me....so cant see how it shorts out. I will try a meter on it. If the float does short it out and is ok, I am sure it will clean and reassemble, the resistance wire can be attached to the terminal again.
 
From what you are stating you could have the magnetic type (and it could be VDO or VD as they are often called for obvious reasons) and the plastic float contains a small circular magnet inside the plastic float. Inside the tube are a series of micro reed switches connected to micro resistors and the earth wire feeds earth from the bottom.

If the fuel is low then the float is low and it opens a switch with very high or very low resistance (dependant upon type) and this resistance is measured by the gauge and alters the needle accordingly, aif the fuel level is higher then the resistance is higher or lower (again, depending upon type) and the gauge reflects this.
 
Hi, no I am sure it is the resistance wire shorted by the float.....I just can't quite work out how. Because the wire has come off one of the top terminals it is unthreaded and just loose.....it could be repaired though if I can sort out the way it works.
It seems it runs like a U shape looped over the bottom fitting on the slide rod.
Then the float has a plastic fitting the wire can hook onto each side so it will slide up and down touching each side of the wire loop.
Had the fitting on the float been metal I can see how that creates the variable resistance....but its plastic as far as I can see.
It is looking likely I will be taking the Starboard one out to drill that one apart and compare. If I cant repair the broken one I shall have to replace two anyway in all expectation to ensure the gauges behave together even if not entirely accurate as they never are!
 
Montemar said:
https://www.asap-supplies.com/vetus-universal-tank-level-sensor-sensor480
Click to expand...

yes, if replaced thats the sort of thing in modern format! but the resistance I think is different to old stuff.

I have now worked mine out, the metal tabs are hidden in the float and were found after thorough clean. I have soldered the resistance wire back on, reassembled it and tensioned the wire by setting the bottom part on the rod using nuts (like a bike spoke it is!)

I have a variable reading on the terminals ranging from about 3 ohms at full to about 35 ohms at empty. Modern ones I think run to 180 ohms but I think this could just be different but not sure!
 
Montemar said:
I believe that different resistances are/were available but your gauges and sensor are probably matched so if you can repair it you may well have the best outcome.
Click to expand...

yes, now it seems two main ones being Euro and american spec. However the 35 ohm empty is quite a low resistance. The USA spec has that full going to 240 empty, the Euro is 180 ohm empty.

That all said the length of wire I have cant be wrong to empty should be about right!

I think if it is not fixed it will end up being two new senders and two new gauges.

Thanks for your interest.
 
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