Fuel sending unit and fuel gauge issue.....
 

Reads between 1/4 - 1/2 full but WRONG because I only had 5 gallons of fuel remaining in the 60 gallon tank ( it filled 55 gallons at pump )

I suppose i need to bend the float arm up a bit, but how much ?
Any ideas ?

1996 Wellcraft V21 specs indicate 60 gallon tank, not the 70 gallons some suggest.
So assuming the spec of 60 is correct, when I have less than 10% fuel remaining, gauge should read less than 1/4 tank .

gas guages on boats are not very dependable. u could take your old one out, run it up and down and see if the needle reacts accordingly. i didn't have a gauge for 20 years. figure your mpg and set your trip odometer on your gps. with the old merc, i got 2 mpg, so i had a 120 mile range. the new motor has a smart guage that computes fuel useage and subtracts from the size of your tank and gives your fuel remaining as a %. i still set my gps and keep track of mpg.

Ok, thanks

I would simply remove all the fuel, remove the sending unit, clean and inspect the bottom of the tank, replace the sending unit with a new one (making sure the float bottoms out correctly), with the tank level (manipulate the winch stand till so) start making notes at "E" and start adding fuel in 5 gallon increments and noting the locations on the gauge.

I've had two people complain to me about their boat getting good gas hours when they fill it up but then once they reach 1/2 tank the motor just eats up the remaining fuel quickly.

The belly tanks are not usually the same dimension/volume per inch of height therefore you would not expect the gauge to read correctly as to the actual fuel volume.

It has probably already been invented, so I won't ask for credit on it. A fuel gauge that can be calibrated at the 1/4, 1/2 and 3/4 marks.
Even MJ could calibrate it!
Picking on the 60 gallon fuel size just add fuel in 15 gallon increments and set the mark accordingly.
Or even one with a removable/replaceable face plate already calibrated for the differing tanks shape.

I just replaced mine. There was a calculation on the package. Also had the benefit of holding the new next to the old unit to compare. Old unit still worked perfectly but the design of top round piece (where the screws go) was terrible and allowed fuel to leak around the screw threads.

Mine was a Moeller.

Haven't run a fuel gauge in several years. A mechanical in tank gauge is on my to do list though, no wires, KISS.

60 gal tank but you will never get 60 into it before the vent spits. And that varies depending on how the boat is sitting. If you're in the water, it really varies...
also, don't bend it, you need to move the arm pivot point up or down and or adjust the length of the arm.
Bending will just make it wrong the other way.

If you read 1/4 when you are near empty, your pivot point is too low,or the arm is too long, or you need to turn the unit so the float arm orients along the centerline of the tank.
(i.e. its hitting the side of the tank)

tsubaki got it right, the v in the belly tank makes it impossible to be accurate thru the full range of the gauge. Watching it as you fill from empty is the ticket...
Of course, once you launch the boat it changes and varies by load.
They can make a calibrated one but $$$$$

I can put about 5 gal in mine after it pegs on full...just not worth messing with it.

I am like spare, 20 years never had a working gauge, never ran out of fuel! just figure out what you use per trip and you should be good, I always fill up at the end of the day so i am always going out on a full tank!

Skunk, I pumped my 60 gal tank last year due to suspected trash in tank. When I filled I got over 64 gallons in it. Probably not 64 "useable" gallons, but 64 nonetheless.

Blue under - I found the same top round piece design so what was different with the new unit you installed ?
Since the tank is plastic, I figured drilling additional holes for added screws wouldn't be able to tighten enough without stripping the plastic top of tank.
Interested in how you corrected this.

I tried to find a pic of one with the same poor design but I couldn't. Here is how it should be - round plate should be flat all the way around where the rim of the screw heads meet the plate. The old one has notches on the outter edge around the screws making it impossible to seal around screws.

On the new unit I bought the screws have some sort of teflon coating around the rim allowing it to seal around the bolts. I still can't get s few of them real tight but the instructions say they don't have to be very tight. Only tight enough to compress the seal around the screws. I have 1 that is stripped out pretty good, and 1 or 2 more moderately stripped out. Seems ok now but the real test will be upon next fill up.

Stock Interweb photo:
https://encrypted-tbn2.gstatic.com/i...ko-8HPwX7IKIbw

Two options... One is larger screws and the other is to rotate the sending unit slightly and make new holes.

Don't just leave it with stripped screws as that is likely to start leaking at any time without warning.

Hi Blue, does your tank have brass or metal threaded inserts for the sending unit screws? My plastic Moeller tank has brass inserts for the screws. I had the same issue last year. Once I cleaned out the corrosion using a small pick and WD40, I found the inserts and carefully ran a bottoming (nearly flat bottom) tap thru to chase the threads and clean them. If you need to, you could tap for slightly larger screws. With the new rubber gasket and clean surfaces mine worked out well, no more leaks , no more smell. Good luck, TJ

Screw holes on tank have metal threads in current position, so rotating would be worse - screws would go into the plastic tank, not the metal threads.

Now with special fuel resistant apoxy applied too, it may be fixed. Will see when I get home.

Still don't like it - should be absolutely secure. It screws down tight - the 5 screws all tight, not stripped, but somehow when pressured at full with fuel, it was weaping out around the rubber gasket.

Didn't realize it was plastic... Was thinking aluminum

How about lock tight on the screws, and using a cork gasket??

You sure it is weeping around the gasket? That is what I thought but it was actually coming from the screw threads

Seems fixed now - used the fuel resistant goop and re tightened.
Filled to over flow and it's dry at the sending unit.
Ran a new ground wire, so gauge working too.......got to keep it all good since it's a rare and extremely valuable V21 series :)

Yeah but how fast will it go?!?!

I want to pull my sending unit to inspect the aluminum tank. I assume I should replace the gasket. I searched ebasic power and didn't find anything. What material should I use to make one and what sealant to goop it (or the old one) in?

Way over 100 mph as in the last scene in " Thelma & Louise " .........

Thanks Smoke

welcome

way to go
 

have one in my v 20 and love it . also have a north star fuel meter just for fun

My Garmin supposedly does something like that too, need to research it and hook one of those up as well.