Fuel Sender

[pjbink]

I'm connecting my underfloor fuel tank back up after getting it repaired. I have trouble remembering how to wire up the fuel sender though. There are two connections - is the centre one positive or negative?

[a boat]

Hi Billfisher, depending on the brand of the sender the centre wire is usually the positive. No big deal if you get it around the wrong way, the gauge will not read right and you will just need to swap the wires going to the gauge. You will not damage the sender or gauge, but as mentioned the centre one is positive.

Cheers,

Huey.

[pjbink]

Hi Billfisher, depending on the brand of the sender the centre wire is usually the positive. No big deal if you get it around the wrong way, the gauge will not read right and you will just need to swap the wires going to the gauge. You will not damage the sender or gauge, but as mentioned the centre one is positive.

Cheers,

Huey.

Thanks huey. I found that out from someone else but you have confirmed it. The bloody thing doesn't work though - but it was only working intermitently before I disconected it. Wether the guage or the sender is the problem makes it a pain trying to fix things so I might just leave it. I have a fair idea of my fuel consumption and always have an extra 25L carry tank on board.

Edited October 18, 2007 by billfisher

[pelican]

Be careful just leaving it. Many of the senders have metal bits in them- yes thay are not all stainless. They deteriorate and can gradually rust. When they stop working it can be a warning sign that they have started to corrode. The centers can corrode out of senders and they can leak fuel. You also don't want wires left under the deck that could be live. To test the sender firstly check the arm / spiral in the tank is moving, the you need a multimeter and just check that it's resistance changes smoothly and constatntly as you move the arm of the sender unit. Sometimes the float on the sender arm if a hollow one can be holed and therefore not float and move the sender arm or spiral. If you think it's your guage you could test it with a new sender to prove that. I have seen sediment in tanks and gum stop senders working properly so it isworth checking your tank out and generally if it isnt the sender unit it is the wiring as boat wiring is rarely done well. With fresh wires just wire directly between sender and guage to diagnose.

6 causes I've come across

Tanks debris, sediment , gum

Sender float dead

Sender jammed

Sender stuffed

Elecrrical connections corroded

Wiring stuffed

guage stuffed

Be caeful as you should always be when around petrol fumes and if you are installing a new sender unit make sure you use the recommended gaskets and sealant if required for the job.

Leaving things not working on boats is a bad thing. Either remove it and make a suitable cover plate and gasket or just fix it. These little failures and maintainance items that occur are not a bad thing an dcan be a warning sign as they make you learn more about your boat. Use it as a chance to check out if there is any debri in tank , check under deck fuel lines , clamps , routing and confirm if there is a spot in the wireing loom where wires have degraded or failed. If it is just a sender get one while the similat ones are still avaliable as the longer you leave it the less chance there is you will find the compatable one cheaply to match your guage and screw holes.

Pel

PS I saw a lot of failures in older sender units with owners who were using ethanol , cheap bad fuel or lots of "fuel treatments" as it seemed to degrade the seals.

Edited October 19, 2007 by pelican

[pjbink]

Thanks for that Pelican. I have disconnected the wiring so its not live anymore. I does seem to be intact though I don't have a multimeter. Its a very old boat so I would doubt that the same model is available. I could probably maange without a fuel guage.

Do you think a piece of plate aluminium would do as a cover? I would have to use a sealant such as Stag of course.

[pelican]

Thanks for that Pelican. I have disconnected the wiring so its not live anymore. I does seem to be intact though I don't have a multimeter. Its a very old boat so I would doubt that the same model is available. I could probably maange without a fuel guage.

Do you think a piece of plate aluminium would do as a cover? I would have to use a sealant such as Stag of course.

We have a guage and we still double check with the trusty length of dowel.

You'd be surprised just how little senders have changed. Just go to manufacturer of guage and you might be in luck.

Use the same material as it is made fron and same grade. Stag would be OK if you can get a very close tolerance fit as it won't fill at all.