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Old 06-15-2013, 06:11 AM   #1
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Fuel gauge adjustment?

My fuel gauge always indicates less than what is actually in the tank (if the tank is half full, it indicates 1/4). Is there any way to compensate for that discrepency?
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Old 06-15-2013, 06:37 AM   #2
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At some point most can be calibrated...see instruction manual or manufacturer's website.

Usually you don't do much more than keep bending the arm or adjusting it's length till you get it close. Also remember if your tank isn't a perfectly level and a perfect rectangle, the "float" tells you a level and not a quantity.

Though they don't necessarily stay that way and even then many are just plain unreliable.

I tow many people each year that say "but the gauge says I have X/X in the tank"...I tell them that the fuel gauge is the most unreliable part of the boat.

Most experienced boaters I know use a stick, hourly calculation, sight gauges, see through tanks or a flo-scan type system.

I am replacing my fuel tanks right now with poly and I don't even plan on hooking up the senders that come with the tank and eliminating the gauges on my dash.
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Old 06-15-2013, 08:08 AM   #3
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There may also be an adjustment screw on the sender but the op is right about the lack of accuracy. I made a dipstick for the tug since it is a straight shot from the fill to the yank. Measured the height of the tank, marked a length of dowel in quarter tank increments and painted with neat epoxy so it wouldn't soak fuel. On the sailboat we replaces the aluminum tank with poly so we can actually see the level in the tank.
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Old 06-15-2013, 09:39 AM   #4
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Fuel tank measurements are complicated by the fact that unless the vessel is perfectly vertical you are measuring an incorrect depth of fuel. Even with our simple sight tubes, there is significant error when the boat is out of trim, as in when one tank has less fuel than the other.
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Old 06-17-2013, 02:01 PM   #5
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I trust dash fuel gauges – not, Not, NOT!! Believe me – I have reasons... from experience!! LOL

Sight gauge on tank side or separate from tank is pretty accurate. Properly calibrated dip stick is fairly accurate. Unfortunately, our Tolly only has electric dash gauges for her two 100 gal tanks; kink in both fuel-fill lines will not allow dipstick of any kind to reach well into, i.e. no where near tank bottom. No sight gauge on tanks... and, because it’s gasoline I don’t think that’s good idea, just in case somehow a rupture/leak were to happen. EEEKK!!

So... I recently purchased dual gauge FloScan that measure to 32 gal per hr each as well as total gals fuel consumed since fillup. Plan to install this summer and calibrate the “total consumed fuel” dial as fillups occur. From what I understand fuel flow per hour / per engine is accurate from onset as to gals per hr being used. What I don’t yet understand is that if gal per hr is accurate on engines then why would the total gallons used need to be calibrated?? That should work off the gals per hr reading... it would seem!!

Anyway, there are many pages of instructions I’ve to read during installation and first use. I believe the FloScan will simply be another tool for guestimating the issues concerning fuel use and fuel available.

I never let my tanks get below before fillup and I’ve pretty darn accurate log calcs to keep me appraised as to fuel circumstances.

Another two methods (I occassionally use when in doubt) for checking fuel remaining in tanks (both methods, although some effort is required for each, are good fail safes to fairly accuratly know what cha actually gots in dem tanks!):

1. IR Heat Gun - - > After boat has sat for days with no use so temp inside both tanks has stabilized to same in the areas of fuel mass as compared to vacent area of air mass... After engines have been run for about one hour (my tanks are abreast of engines in same compartment... so this works via heat trensfer to tanks) and heat has developed upon the tanks’ walls I open salon floor hatches and at wherever is the level of fuel the IR Gun will show marked temp difference (10 +/-degrees f) of fluid filled area and air filled area, because, the tank’s metal in air mass area heats-up to a higher temp much quicker than metal in the dense fluid mass area. Now, if you run the engines too long then temps in both areas will begin go converge, and, if you run em too short then the air mass area tank metal will not have had time to heat up compared to fluid mass area. Properly actuated I believe I can determine fill level to within an inch.
2. Engine stethoscope (real doctor stethoscope might work even better!) With tanks hot or cold place stethoscope on a level and gently ping against tank wall with a metal object. By moving stethoscope up and down tank wall you will soon assertain what has fluid in back of it and what is filled with air. Properly actuated I believe I can determine fill level to within two inches.

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Old 06-17-2013, 04:06 PM   #6
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I've run my tanks, individually, to "zero" inches without running out of fuel. Suppose one has to "test the limits."

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Old 06-19-2013, 07:08 AM   #7
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A calibrated flo scan is a great solution as it has other uses.
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Old 06-19-2013, 07:33 AM   #8
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A calibrated flo scan is a great solution as it has other uses.
A FloScan system is high on my must-buy list. But they sure don't make it easy.

The big retailers don't carry many choices. The FloScan web site lists a thousand confusing options. The flow sensors are sold separately from the display units, and it's not even clear to me what I need to buy, much less what I want.

I have two digital tachs on my upper helm that are useless, not sure if it's the units themselves or the wiring. So I like the FloScan option with the tach built in. They would fit right in the same holes. Then again, I like the one with both tachs side-by-side in one gauge. And just looking at the prices on the flow sensors (I need four!) is scary.
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Old 06-19-2013, 02:07 PM   #9
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Anyone with experience with the exterior tank mointors applied to the fuel ank exterior ?
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Old 06-20-2013, 06:38 AM   #10
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"The flow sensors are sold separately from the display units, and it's not even clear to me what I need to buy, much less what I want."

This is because different engines have a different RETURN flow.

The sensor set has to be matched to the specific engine.
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Old 06-20-2013, 08:56 AM   #11
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"The flow sensors are sold separately from the display units, and it's not even clear to me what I need to buy, much less what I want."

This is because different engines have a different RETURN flow.

The sensor set has to be matched to the specific engine.
Hey, Fred - Yous gots me ta thinken!

The gasoline dual gauge FloScan set I picked up at estate sale in sealed factory plastic with unbroken seals on its cardboard box inside the plastic came with gauges and sensors in the box. It had recently been purchased to be installed onto a mid 1970's 34' Uniflite convertible. Those boats usually had 318 Chrysler or 350 GM for gassers. Have you knowledge as to compatibility for FS sensors in comparison of 318s to 350s? I have 1977 350 cid 255 hp Mercruisers. Guess I should call FS engineering with product in hand for serial #'s. Maybe I made a boo boo - LOL... If so, onto CL it goes!
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Old 06-20-2013, 09:27 AM   #12
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Hey, Fred - Yous gots me ta thinken!

The gasoline dual gauge FloScan set I picked up at estate sale in sealed factory plastic with unbroken seals on its cardboard box inside the plastic came with gauges and sensors in the box. It had recently been purchased to be installed onto a mid 1970's 34' Uniflite convertible. Those boats usually had 318 Chrysler or 350 GM for gassers. Have you knowledge as to compatibility for FS sensors in comparison of 318s to 350s? I have 1977 350 cid 255 hp Mercruisers. Guess I should call FS engineering with product in hand for serial #'s. Maybe I made a boo boo - LOL... If so, onto CL it goes!
been awhile since I've installed them buuuutttt....I think......as long as they can handle the fuel flow and hose size..I think they are all the same...you calibrate after a few tankfulls...the sensors are generic as to flow.
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Old 06-23-2013, 01:35 PM   #13
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Foto - Fred stole my thunder - I, too, went through the fuel level adjustment & cal issue - finally threw in the towel and bought a FloScan. Pretty bulletproof and even I could install it and get it correctly set up. Now I know what fuel status is with remarkable accuracy.

CaptTom - agree on the literature / choices - the FloScan guys are great - just call 'em.

Art - particularly since it's a gasser (no return flow issues), I think they'll work fine - but. just call the FloScan people - easy to talk to.
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Old 06-23-2013, 03:50 PM   #14
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>>>The FloScan web site lists a thousand confusing options. The flow sensors are sold separately from the display units, and it's not even clear to me what I need to buy, much less what I want.<<<

Has not been my experience. On the FloScan site, select diesel, American, and it will come up and you select engine manufacturers and then engine model and then the part number for a FloScan system comes up. Package comes with sensors, pulsation dampers, gauges and hardware. The tach display will run off several types of pickups including the signal from the alternator.

I just bought a dual diesel system from marinedeal.com. Price was better than direct from FloScan.

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Old 06-23-2013, 07:35 PM   #15
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Art - correction due, hadn't had enough coffee when I posted - I assumed that your engines were carb'd and not fuel injected. If not carb'd then fuel return is an issue. If carb'd sensors should be good, but I'd still talk to FS.
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Old 06-23-2013, 09:51 PM   #16
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Art - correction due, hadn't had enough coffee when I posted - I assumed that your engines were carb'd and not fuel injected. If not carb'd then fuel return is an issue. If carb'd sensors should be good, but I'd still talk to FS.
TY - No prob... "Coffee COffee, COFFEE - Cause I Feel SOOO FINE!!

My cool ol' gassers are carbed...I'll speak w/ FS HQ engineers afore installing (maybe even as installation occurs - lol). It might be that some time passes till install happens. I've projects under way... boats, houses, property, a classic car and truck... not to mention runnen businesses and playen w/ family and friends. I keep every day full... Luven It All!
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Old 06-24-2013, 04:27 PM   #17
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My fuel gage is extremely accurate. I have one in the starboard tank and I can predict within 10 % how much I can take on board in BOTH tanks.
My Mainship was the same way. Exteremely accurate.
Maybe I am lucky, or maybe I have figured out how ro read the gages.
Who knows?
I'll take luck.
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