Dead fuel gauge- where to start looking for repair

[Forester125]

I"m new to being a boat owner and have a dead fuel gauge in the counsel but the fuel tank is full. 1985 Forester 166 with stainless built-in fuel tank, about 15-18 gallons. Would I start with the gauge itself and replace it or should I start with the "device" that's in the tank? Thanks for your help!

 

[Silvertip]

Re: Dead fuel gauge- where to start looking for repair

You don't start by replacing ANYTHING! You troubleshoot, isolate and THEN repair. It is a bunch cheaper than throwing parts the problem. The fuel system diagram has been posted in this forum at least 20 or 30 times so the "Search" function would have turned it up along with troubleshooting tips. But -- being the nice guy I am (others will dispute that) here is one more time.

1) Key on.
2) jumper the "S" terminal on the gauge to the ground terminal on the gauge. Does the gauge peg full? Yes = good gauge. No = loss of +12 volts or ground at the gauge. Fix it then retest.
3) If gauge is ok, disconnect the wire on the "S" terminal at the gauge.
4) Measure the resistance to ground. 33 ohms = full tank, 109 ohms = 1/2 tank and 240 ohms (all approximate). If that measure ok and previous gauge test is ok then the system should work. If the resistance checks are not accurate for however much fuel is in the tank, then repeat this test at the sender. If the measurements are still incorrect, replace the sender. If the measurements are ok and the sender wire is ok then the system should work.

Heres' the diagram.

 

[rjmay]

Re: Dead fuel gauge- where to start looking for repair

Great info and schematic. My newbie question is: how do you define "S" terminal, and How do I know for sure I have the right wire at the gauge? Do I look for the Pink wire?
In my case, [Sea Ray 180 Bowrider] The jump test shows the gauge working. Also the top of the fuel tank CAN collect water and the top plate of the sender [or gasket] is corroded. [10 years old] Can I apply any type of caulk or protectant to ensure no water infiltration into the tank?
I'd rather not change the sender if I find it is working....

 

[NYBo]

Re: Dead fuel gauge- where to start looking for repair

"S" stands for "signal" or "sender". Many boats have a pink wire for the signal wire from the fuel tank, but check the color of the wire attached to the sending unit at the fuel tank. Of course, a previous owner could have replaced or spliced in a wire of any color.

Any idea why water is reaching the top of the fuel tank? That area is usually fairly well-protected from water.

 

[rjmay]

Re: Dead fuel gauge- where to start looking for repair

Thank you. Yes the tank is protected, but heavy splashing or washing could get water to the tank, which is ever so slightly concave, so what ever moisture there is gets to the sender. If the sender passes the test at the gauge, is there a caulk that you would recommend to ensure a water tight fit?
ps: I just learned I am guilty of 'hijacking' this post. Apologies to the original poster. I hope this serves to help the original poster, and anyone else with a problem that leads them to this thread.
Thanks again.
Rich

 

[Silvertip]

Re: Dead fuel gauge- where to start looking for repair

The "S" terminal is stamped or on a label on the back of the gauge (just like shown in the diagram above) Grin!!!!!

 

[rjmay]

Re: Dead fuel gauge- where to start looking for repair

The "S" terminal is stamped or on a label on the back of the gauge (just like shown in the diagram above) Grin!!!!!

Well Duh! I guess if I looked I would have seen it...! Regarding the gauge not registering the fuel level:
If the jump at the sender gets the gauge to peg full, should I not automatically assume the sender is bad? The wiring obviously is good. The gauge is working.... Get a sender? Is this something a novice should be able to do easily enough?

 

[Silvertip]

Re: Dead fuel gauge- where to start looking for repair

No - because the gauge pegs proves ONLY that the gauge itself is good (meaning that it has power, ground and the gauge is functional). It does not mean the sender wire or its connections are ok. You are incorrect to jump to the sender. The wire from the "S" terminal on the gauge runs the length of the boat to the sender. It can be broken or disconnected at either or both ends, or shorted to ground anywhere in between (although that would peg the gauge). If you would do a SEARCH on this forum for "FUEL GAUGE PROBLEM" you would find the troubleshooting info in at least 30 or 75 or so responses and several of those tests were explained in the last few days.

Whether or not a novice can replace a sender or troubleshoot the system depends on the abilities of a novice, If you don't have a test light or multi-meter and know how to use either of them, your choice is to replace the sender and see what happens which is the expensive way to find out that was not the problem. Electrical components are not returnable like lots of other stuff. Only you know your abilities.

 

[mustang5x0]

Re: Dead fuel gauge- where to start looking for repair

Hello your lay out of the typical fuel to gauge and battery is awsome MY BIG issue is that my sending unit has a three wires from it and i have tried the S wire trick and the guage took off to full CAN anyone help me either find a replacement sending unit with three wires,1 wire is pink,2 wire is black 3 wire is purple all factory wiring but every place i have looked or talk to said they have never seen this type of sending unit before they are all 2 wire PLEASE HELP!!!!!!,,,P.S. the sending unit i have had out of the tank and it has no float system it's only a rod had the tank checked and is clear of anything other then fuel in it,,THANK YOU SO MUCH

 

[Silvertip]

Re: Dead fuel gauge- where to start looking for repair

Check the sending unit carefully for a manufacturers name and part or model number. The Google or Yahoo search using that name and number. Chances are the tank has a standard sender opening and bolt patter so a typical float system sender could be used. the sender you have has 12 volts, ground, and sender connections. The ground connection is a wire whereas the two wire senders you are finding may have a ground connection via a spade terminal on the metal part of the mounting flange so it really is a three wire sender. The sender you have is more accurate than the swing arm type so replace it with the same type. Any above all, make sure the one you have is bad. Measure the resistance of the sender (ground to the S wire). It should read somewhere between 33 - 240 ohms depending on the orientation of the entire sender.