Fuel gauge reads full all the time.

[Mataji]

This appears to have been a problem for some time as I can see from the boats history that previous owners have had the same problem. Old bills I received with the boat show that the problem has been investigated and the sender has been changed. Still reading full. Any ideas?

 

[earlybird]

Wiring fault between sender and display?
Further thought, IIRC, some gauges rely on a voltage reducer to provide the power supply. If so, it could be faulty.

 

[Dan Tribe]

Wiring fault between sender and display?

That sounds most likely. It happened to mine last weekend. Stuff gets chucked in the cockpit locker and the cable became disconnected. . I must re-route that.

 

[Mataji]

Thought it might be as simple as a wiring fault, a connection earthing or something. It’s well nigh impossible to trace the route of the wiring and very difficult to get to the back of the display. I have tried simply reversing the connections at the sender but still reads full after this.

 

[simonfraser]

Mine reads fuller the higher the resistance is ....
Who dreamt that up
So all you need are some dirty contacts, which is what i had, I suggest you find the contacts on top of the tank and clean / connect those again.

 

[matthewriches]

Depending on the style of sender & gauge combination will depend on likely fault. Assume it is a variable resistance sender with a compatible gauge.... as most pleasure boats are... Euro range is say between 0 - 180 ohms. Depending on manufacturer depends on whether 0 is full or 180 is full, etc, etc....

Can you see a part number on the sender? You can then find the type and then the range assuming a resistance sender. Then check the contents of the tank in relation to the reading given.


I had one of my fuel tank senders fail, it was the float that had become detached so the arm sunk and gave a permanent "empty" reading.

 

[Mike k]

I have just replaced the fuel level sender kit as my reading suddenly went to empty and I knew it was full. I put a search on ebay and couldn't believe my luck when one came up and got it for 99p. Anyway it works perfect now.The way I tested it was to remove it from the tank but keep the wiring in tact and raise and lower the float and watch the gauge

 

[vas]

helped a friend sort out fresh water tank gauge on a P45.
used another cable wired between the sender and gauge, with sender removed.
Made sure the meter was showing what it should, and the gauge moved properly.
Then refitted the gauge, cleaned all contacts carefully, refitted old cable and after a couple of goes it worked.

However, that means you HAVE to remove the gauge and check behind how many Volts it gets and if it does receive the right values from the sender.

cheers

V.

 

[macd]

Mataji: you write that the gauge reads full "all the time". That would include when the engine electrics are switched off, although perhaps that's not what you mean? If it is, suspect the gauge to be knackered.

 

[alan]

VDO European gauges will read full when open circuit (VDO American gauges read empty for open circuit). I made up a small tester consisting of a variable resistor (0 to 200 ohms IIRC) and use this to check whether the gauge is working or not. I have used it on my boats and on friends' boats and so far it it has always been the sender in the tank that is faulty. The worse case I had was that the sender would work when full and down to 3/4, then the slider would stick and continue show 3/4 even when empty!!!!

 

[neil1967]

I have just replaced the sender in my fuel tank - changed from a lever arm type to a circular float moving up and down a rod. Replacement was simple, with even the mounting holes on the sender aligning. If the wiring is not at fault, my bet would always be on the sender - it's in a bit of a harsh environment.

 

[Martin_J]

Depending on the style of sender & gauge combination will depend on likely fault. Assume it is a variable resistance sender with a compatible gauge.... as most pleasure boats are... Euro range is say between 0 - 180 ohms. Depending on manufacturer depends on whether 0 is full or 180 is full, etc, etc....
.

As Matthew says..

With EU Wema gauges, a bad sender connection will show as full whereas with a US Wema gauge it will show empty with a bad sender connection.

RESISTANCE Ω on Wema senders

 

[matthewriches]

As we talk about this, I see my other fuel tank has gone, so I may be replacing that now

I did trial an echo sounder type fuel tank sender last year for a manufacturer but that didn’t give reliable results either. Speaking to a world single handed cruiser, he reckons the most reliable type are the ones you pump up with a little hand pump??