Fuel Tank gage issues

[Major Woods]

Have 2004 GW Marlin 300.
Long trip this weekend, ran the main tank down till the fuel gage stated flashing on the last bar (Warning Empty), switched tanks and kept on going.
When back at the marina, filled the tank up and it only took 115 gallons.

The owners manual says its a 150 gallon tank, is the fuel gage not being even close to accurate a normal situation?
Is there a fix, put in aftermarket sender unit?

Thanks

 

[Hookup1]

My fuel tank gauge is reasonably accurate. When it starts flashing the tank is very low. Gauges are affected by the attitude of the boat. If you are bow high all the fuel runs to the back of the tank and will give you higher readings. When you come off plane and level out (you might even go slightly bow down) and run out of fuel (pickups aft in tank). Gauges are a guide - not the same as your car!

That said you can test your sending unit (ohm meter slide pickup). If sending unit was replaced they may have put the wrong length on in.

Or just replace it with a WEMA style sender (I did both of mine). Make sure your tank is down about a 1/4 tank before pulling the sender. Sender is clocked and will only bolt in one way for screws to line up. Use a new gasket. Permatex fuel-safe gasket prep if the tank is badly corroded around sending unit.

 

[trapper]

Hookup1 do you know what is left in the tank in gallons or litres when the Yamaha gauge starts flashing?

 

[Neeen]

I would be curious too - actually just had this happen, ran the tanks down to one bar flashing (at dock, not moving). yamaha electronic trip gauge shows 178gals used. the fuel tank spec says the tank holds 230gal. This would leave 50gals reserve at flashing one level bar. I filled the tank and it did take 178 gals. and I know it is full. anyone else have matching numbers?

 

[seasick]

Have 2004 GW Marlin 300.
Long trip this weekend, ran the main tank down till the fuel gage stated flashing on the last bar (Warning Empty), switched tanks and kept on going.
When back at the marina, filled the tank up and it only took 115 gallons.

The owners manual says its a 150 gallon tank, is the fuel gage not being even close to accurate a normal situation?
Is there a fix, put in aftermarket sender unit?

Thanks

By the very nature of boats and hull angles, the gauge is not as precise as folks think.
Just by walking around the deck can change the angle of the tank and that will skew the reading. If everything was level and not moving, the flashing bar , when it starts flashing does not mean the tank is empty, it indicates that an eighth or less of the range of the sender.
Depending on the type of sender, KUS style linear or old fashion swing float, that reading can mean a decent range of gas quantities. In addition, the sender itself sits above the tank bottom, so that empty to the sender is not actually an empty tank. Note that the flashing bar can represent an eigth or so or zero ( and there is still gas in the tank below the sender.
The bottom line is that if you rely on the sender information to accurately tell you how much gas you have, you will someday run out of gas
On my boat I can get a more accurate estimate by noting the reading at rest and then when on plane. Since the hull will have a steeper angle on plane, the gas gauge will read a higher level than the actual level.

 

[Hookup1]

Hookup1 do you know what is left in the tank in gallons or litres when the Yamaha gauge starts flashing?

The bottom bar is sold when the sending unit is at 1/8 of a tank and starts flashing below that. Just remember that when you are at the point of the gauge flashing and you are on plane you are in the danger zone. When you come off plane you may (I have) stalled the engine out.

It's possible you have a bad or incorrectly sized sending unit. You should plan to pull your sending unit and use a wooden yard stick, wood ruler or paint stirrer to check the tank depth and compare to your sending unit. If it's not the correct length that could explain what you saw. It's also possible you have a bad sending unit. My gauges do not have any switch settings and only reports what it reads.

Specs say 150 and 156 gallon fuel tanks. When you pop the pie plate cover over the sending unit there should be a certification sticker there from the tank manufacturer to give you gallons.

 

[Sardinia306Canyon]

On my BW 23 Outrage i could estimate remaining fuel rather correct if i went alone aboard, sat on the leaning post and checked then. Always alone and resting!

If your engines and electronics allow that, use "Remaining Fuel" and not the fuel senders in the tank.
On all the boats i had that remaining fuel was correct with a difference of 1-2 Gallons of up to 300 gallons.
Just get used after refueling to at the amount of gasoline you filled and/or fill to full and set tanks to full.
I can do that either on my CL+ gauge or on my Garmin MFD's
Chris

 

[tech_dog]

You probably have a bad sender, or maybe the wrong sender for the tank. I had inconsistent readings for a long time, and finally replaced my sender. Upon pulling it out I realized someone had replaced it with a unit 1" shorter than OEM.

Going back to the exact match OEM sender got me back to consistent tank readings that matched reality.

T.

 

[TLCObsession]

You probably have a bad sender, or maybe the wrong sender for the tank. I had inconsistent readings for a long time, and finally replaced my sender. Upon pulling it out I realized someone had replaced it with a unit 1" shorter than OEM.

Going back to the exact match OEM sender got me back to consistent tank readings that matched reality.

T.

Could you post what you bought and where?

 

[tech_dog]

Could you post what you bought and where?

I bought this for my 1996 Tournament 192 with a 60 gallon poly tank: KUS 151330 SSS - 9 inch Single Station Sender Fuel Sender: https://www.ebay.com/itm/225810322550

On my boat it's pretty consistent with 6-7 gallons per LCD segment on the Yamaha gauge, and the last segment starts flashing at 5-6 gallons remaining. I have the original Yamaha 2 stroke, and your results may vary if you've repowered or moved weight.

 

[DennisG01]

Could you post what you bought and where?

The reed style is generally longer lasting and a bit more reliable - but the lever style is perfectly fine, too. If you have a local marine store, just take yours in and you'll likely walk out with a new one that day. They're really a dime-a-dozen kind of part and available everywhere. What someone else uses on their boat MAY not be the right size for yours. Measure the tank depth if you need to.

 

[everwhom]

I had a sender go bad on my 330 Express, and I contacted Grady to get the right size. The original was a 1/2" longer than what was easily available, so I replaced with a slightly shorter sender. I think it's bad if the sender it too long because it may damage the tank!

Replacing was easy - I purchased directly from KUS and also replaced the gasket.

 

[Fishtales]

The tanks are 150 and 156 gals on early 2000 models like yours. They did get a tad smaller in later years. It's likely the sending unit or as stated accuracy. I'd watch it and see if it is consistent. If so, either live with it or correct the issue.

 

[SkunkBoat]

In the olden times there were float/arm sending units. they were terrible. I will not discuss them...

Most fuel senders in recent decades are 8 segment reed switch/hall effect sensors. They have a rod with 8 equally spaced sensors. They tell you the level of fuel based on the highest one that is under the surface of the fuel. So, if the fuel is between sensors, it tells you the lower one. It can't tell you anything below the bottom sensor. It can't tell you how much fuel is above the highest sensor when you fill the tank.


In the picture, the example tank is divided in 4 equal heights (use your imagination because I didn't get the lines exact...) The top 3 hold equal volume of fuel but the bottom 1/4 holds less. Also the bottom 1/8 holds less than the 2nd 1/8th up.




So...fuel gauges display fuel "level" or "height" in the tank and there is dead space at the top and bottom. Also, the tank volume is not linear to height.
Fuel gauges have nothing to do with Gallons.

So NOBODY has a fuel gauge that works perfectly. Although a flat bottom tank would be more accurate.
Different models may have different V shapes and so different inaccuracies.
My point is...don't expect much. Learn what your gauges look like at different volumes(gallons) of fuel.

Also, the tilt of the tank effects the "level" of the fuel at the rear of the tank where the sender is located. The tilt of the tank also effects how much you can "fill" the tank

I have two tanks. When I fill them I can burn almost 20 gallons from the main tank before the gauge even moves from FULL.
At "half" I am actually 10 or 15 gallons less than a true 1/2 tank.
The gauge readings on my two tanks (130 and 120) could not be more different. They are v bottom but one is tall (deep) and the other is long and shallow.

If you want to accurately know how many gallons of fuel you have, you must use your fuel burn calculations in your MFD.
If you have modern fuel injected motors your motor's computer very accurately measure fuel burn.
Your MFD uses this to "count down" fuel and to also give you calculated range.
When refueling you must Reset your Trip and tell it how much fuel you have added. If you forget to do that, you can use your Fuel Gauge as a fallback.

 

[Sardinia306Canyon]

Your MFD uses this to "count down" fuel and to also give you calculated range.

Also the newer Yamaha tft panel engine displays do that and it can be reset on the display itself.
The only problem i found is that for whatever reason and even if fuel capacity is correctly set to 1180 Liter the Yamaha gauge show not more than 980 liter so the Yahaha gauge is 200 liter off, but my Garmin 8412 show the correct value.

I use either the values from the Yamaha gauges i have and had, but mostly the Garmin Fuel screen and both are spot on.
The calculated range is - same as in a car - not very reliable and should carefully be used as as it calculate range from actual fuel flow, so it varies with changing rpm changes / boat speed.
Chris

 

[TLCObsession]

As an FYI - I pulled my sender to measure to order a replacement. The outer aluminum tube and float were no longer attached. I think I can snare or grab the tube, but the float and whatever kept it on the tube are not visible. They probably won't do any damage, but i would prefer to get them out of my tank. Not sure if the float magnets are strong enough to grap on to something like a pickup magnet.

Boat is a 2002 208 Adventure with an 82 gallon plastic tank.

 

[Beyond A Wake]

Dont assume anything is magnetic in the tank (or on the boat) . They tend to be aluminum or stainless but not iron.
Only if you have a proper inspection hole can you see maybe with a scope or so and using pinchers fish something out. Of course a partially fidled tank is hard to penetrate with light for seeing small parts.
If you have a "plastic" tank you may be able to paint lines at different heights giving a better understanding of fuel level even Gallons in tank.
There are several threads on fuel gauges/tanks so just look around and enjoy the reading..
H

 

[seasick]

I think the OP was referring to the float and specifically a WEMA style sender with donut float on shaft. In that case a magnet would probably grab onto it .The funny thing is that the float should 'Float' so it should be on the surface somewhere whereas the tube would likely be laying on the bottom. . Of course if the OP is referring to an old style swing arm float, none of what I said applies