Fuel Level Sensor Replacement

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Staff member
Supporting Member
Feb 18, 2006
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Danversport, MA
Finally, my fuel tank sensor replacement project is complete. I was about two months behind schedule thanks to the whacky monsoon weather up here in the Northeast. I couldn't burn the remaining MTBE fuel in my tank fast enough, because the weather put our summer so far behind.

I had three objectives in this project: 1.) Replace my fuel sensor unit 2.) Convert from stock Yamaha fuel filter to Racor clear bowl type 3.) Survive a conversion from MTBE to Ethanol-blended fuel. My fuel sending unit was \"sticking\" at 3/4 full for weeks, then falling abruptly to 1/4 full or less.

I have a 2000 25MVSC with a 126 gallon tank and run a single 225.

I ordered a new stainless steel fuel sending unit for $40 from WEMA USA,(Sensing Quality, Gauging Success! | Home) thanks to recommendations from Danielb. The folks at WEMA USA were very helpful, and the unit arrived in less than a week. Thanks again Daniel for the information. Here is the post with the vendor info


The top of the old sending unit was really cruddy looking. Lots of mildew due to deck leakage from the old Tempress deck plates was evident. I have since cleaned things up and replaced the O-Rings and re-seated the flanges of all Temnpress deckplates. The biggest problem I had during the entire process was removing the old machine screws that held in the old sensor. The screw heads were so badly distorted that it was tough to tell if they were Phillips or Torx. Three were recognizably Phillips and two looked like they had been stripped (rounded out) by a power tool during installation. It was necessary to use micro-visegrips and lots of WD40 to remove two of the stubborn stripped screws. I was concerned with snapping a head off and having to drill and extract a screw. Patience and perseverance worked. All screws were replaced during the re-install.


When I finally got the old sensor out I found that there was more fuel in the tank than I had thought. The tank sensor stops about an inch above the tank bottom, which is also where the fuel pickup tube stops. The tank is about 12.5 inches in depth. This means that there is roughly ten gallons of fuel per inch of tank depth (assuming uniform tank walls and floor). I had two \"bars\" on my Yamaha fuel guage and 4.5 inches of fuel left in the tank. About 45 gallons. So I ran a couple of after-work twilight cruises to burn fuel down to a manageable 30 gallons.

The good news was that the tank bottom (see photo below) was whistle clean. No sludge, no water, no crap, no nuttin. Just shiny clean aluminum. I used a small dental mirror to insert into the tank and inspect as much of the bottom as possible. I had a chance to re-inspect the bottom over several days running (to burn excess fuel) so if there were a lense of water or sludge, I should have seen some evidence of it.


Based on what I have learned here on Classic Parker, I wanted to get as much of the MTBE fuel out of the tank before I switched over to Ethanol fuel. I used this hand pump (fuel-rated version of a bilge pump) that I found at Boater's World to pump out as much of the remaining fuel as possible, about 20 gallons. I wound up leaving about ten gallons in the tank.


Once the tank was as empty as I could possible get it, I switched over the sensor wires and installed the new fuel sensor. Here is a side-by-sde comparison of the old aluminum sensor and the new stainless one (left).


I removed the new baby-blue Yamaha fuel filter using an child's beach sand pail as secondary containment to catch drips.


The new Racor spin-on was a quick, clean replacement. Replace with Ethanol-based fuel, prime the new filter, and go. Things look good so far.


Lessons learned:

1.) Classic Parker is chock full of great advise and tips, like DanielB's replacement fuel sensor tip, and Dale's Racor filter info.

2.) Keeping your deckplates water-tight involves -two- sealing surfaces, the O-ring, and the flange-to-deck seal. The latter is most critical and often overlooked. Water does not have to overcome gravity to penetrate that one.

3.) If there are 5 critical sealing machine screws in an assembly that absolutely -must- be removed, at least one will be toast. :roll:


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Excellent project documentation! :D
This is an item that I need to put on my list of 'things to-do'.
Since I have a full canvas cover on the boat when not in use, I haven't re-sealed the deck plates. Guess I should do that one of these days soon while the WX is so hot, and the fishing is crappy. Gotta get ready for the fall striper run, and a CBBT trip. :D :D :D
Reseating them with new "caulk-of-your-choice" is such a simple thing I am kicking myself that I didn't do it sooner. It makes a huge quality-of-life difference to your gas tank. All last year I was blaming the O-rings for moisture on the tank top until I bought a new set of O-rings and replaced them completely, and still had water hitting the gas tank top. :cry:

When you unscrew the flanges from the deck and look underneath you will instantly know if you've had a problem, as there will be dirt-tracks where water has seeped through.

If you think about the physics involved, with water having to overcome gravity to flow up over the top of the deck flange and sit on top of the O-ring to leak, it makes sense. The path of least resistance is between the deckflange and the deck.

It's not a design flaw, it's just a maintenance thing. I like the extremely low profile of the Tempress models that are OEM. I am barefoot in the cockpit 90% of the time, and a higher-profile deckplate would kill me. :shock:

So from now on, every other year, I will re-seat the deck flanges as a regular maintenance item. Quick and easy to do and big return on your investment. :lol:
cbigma":2ymcz6r9 said:
It's not a design flaw, it's just a maintenance thing ...

So from now on, every other year, I will re-seat the deck flanges as a regular maintenance item.
Ya' know, most surveyors recommend rebedding ALL deck hardware every 2-3 seasons, specially those subjext to stress, i.e., cleats. I bet the deck plates go through a lot of expansion and contraction being in view al the time, being thermoplastic, et al ...

I also replace the O-Rings every other season or so (watch them) and keep them greased with OMC/Bomb "Triple guard" waterproof synthetic grease.
That Triple Guard grease is the stickiest most tenacious stuff I've ever used. I keep a squeeze tube aboard at all times -- I too use it on "O" rings and in addition to zerks, I regularly use it on the prop shaft and tilt tube.
That's good to hear Daniel, so far I haven't had the "hang-ups" that I had with the old aluminum one. Thanks again for the info about the WEMA folks. I wish all the boat industry parts people were as genuine and responsive to deal with as those guys. 8)

Absolutely works with the Yamaha display. One of the easiest OEM replacements I've ever done. Everything aligned well, and fit perfectly.

Like DanielB said, the most important thing to tell them is the depth of your tank (which dictates the length of the gauge). They allow an inch of free space below the gauge for tank flex etc.

My tank was 13 inches deep. I'm sure the folks at Parker could give you the dimensions, or WEMA themselves may have a listing of all Parker models.

great post!

this is the kind of nitty gritty that makes this site shine.....i did this
job about three years back....i chose the livorsi model of electronic-
no-moving-parts sender......it is nice because it allows calibration
after installation......i got a custom length to place it about 3-4 inches
off the bottom.....this both gives me a handsome reserve once i hit
"e", but it keeps the sender out of the goop along the bottom......i
tried a mirror too and saw only a half cup of water in one corner.....
the new sender is much more accurate.

i ran the fuel down to where the bottom of the sender was, so that it
registered "e".....still had 10-15 gallons beneath the sensor tip....then i
slowly added gas and noted the 1/4, 1/2, and 3/4 amounts on the gas
pump......it came to 37, 64, and 84 gallons with the "f" being 104......
redoing all the connections showed that the environment down in the
tank confines is brutal.....i sprayed the whole thing with "t-9" thoroughly...
i used a goo for the seal (vs the cork supplied), eg. "permatex"...

the pink and black lead worked fine with the gauge on the dash oem....
this is an excellent upgrade for any/every parker boat.......i would suggest the following upgrades AT THE SAME TIME......add a spare #10g
green wire back to the battery neg post and/or the block...the other is
up front on the fill pipe, and i would redo that one also......test them
when done for continuity using a dmm.......a yearly test of these grounds
can be a regular checkup on the fuel system.......second, if your boat is
ten years or older, REPLACE ALL HOSES!.....the vent, the fill, and the feed
hoses......use only trident or shields brand of top-rated hose, and use
only "awab" (real) ss clamps, please..;...the others are markedly inferior
incl the "ideal", et al......another little project is to run #10g green wire
from the racor to either the batt neg post or the block.....racor doesnt
mention it, but filters need full grounding since they are bolted to glass
for mechanical attachment.......lastly, have a low threshold to both
replace the vent fitting through the topsides and to pull, inspect, and
rebed the fill fitting, including the o-ring on the screwcap......dan
bump as this is a great post Cbigma.

1.How did you wire the new sending unit in. i have Yama gauges, it seems this just went right into the gauge if wires long enough or did you splice into the old wires ?
2. Any concerns with with fuel in tank and changing units, batteries off, good breeze to move fumes any other safety issues outside of normal precautions ?
POGE":2hxa9xdq said:
bump as this is a great post Cbigma.

1.How did you wire the new sending unit in. i have Yama gauges, it seems this just went right into the gauge if wires long enough or did you splice into the old wires ?
2. Any concerns with with fuel in tank and changing units, batteries off, good breeze to move fumes any other safety issues outside of normal precautions ?

1.) This was a plug-and-play replacement of the original unit, so I just butt-spliced the new sending unit into the same harness as the old one. Same color code etc. Shrink wrapped over the butt-splices. The cables supplied with the replacement sender weren't long enough to do anything else.

2.) All the standard precautions working with gas liquid and vapor apply here. I did the work at my slip where there was plenty of wind so ventilation wasn't an issue. I think I was more nervous about snapping a screw off than the explosion potential!

3.) Visually confirming that the tank bottom was "whistle-clean" gave me great peace of mind after hearing the horror stories about the kind of spooge one can accumulate in fuel tanks from years of Dockside fueling.