Gas tank sending unit/gauge question

Discussion in 'General Discussion' started by 55Trucker, Sep 15, 2022.

  1. 55Trucker

    55Trucker New Member

    17
    Aug 15, 2022
    Otisfield, ME
    1998 SeaRay 175 Bowrider with Mercruiser 3.0 and Aplha1 Gen 2 outdrive
    Mercruiser 3.0 and Aplha1 Gen 2 outdrive
    Hi everyone, we recently bought a 1998 SeaRay 175 Bowrider, with a Mercruiser 3.0L motor and 20 gallon fuel tank.

    Yesterday we got stuck on the pond. The fuel gauge read 1/2, but the tank ran dry.

    My questions are:

    1) is the problem more likely to be the sending unit or the gauge?
    2) The parts document for this boat shows part #912667 for the gauge, and part #782664 for the sending unit. Unfortunately, I can't find either of these part numbers online. Do you have any suggestions for how I can fix this issue?

    Thank you.
     
  2. dwna1a

    dwna1a Well-Known Member PLATINUM Sponsor

    Apr 23, 2012
    James River
    88 Weekender 300 "Seahorse"
    Twins 350
    Sounds to me it’s the sending unit in the tank. How big is the tank? Have you refilled the tank since it stopped on you?
     
  3. 55Trucker

    55Trucker New Member

    17
    Aug 15, 2022
    Otisfield, ME
    1998 SeaRay 175 Bowrider with Mercruiser 3.0 and Aplha1 Gen 2 outdrive
    Mercruiser 3.0 and Aplha1 Gen 2 outdrive
    It is a 20 gallon tank. When I originally filled it after buying the boat the gauge showed as full. We used it a bunch of times, and the gauge registered a notch above 1/2, but then we ran out of gas because I thought it was accurate. I threw in 4 gallons today to get it started again and it showed as almost full.
     
  4. swaterhouse

    swaterhouse Well-Known Member GOLD Sponsor

    Jan 7, 2015
    Mattapoisett, MA
    2008 58 DB
    MAN CRM 900
    techmitch likes this.
  5. KrazyKarl

    KrazyKarl Member

    43
    Jun 26, 2022
    1999 190CC Sea Ray
    4.3L Alpha (190 PHP) MCM stern drive
    I had the same problem but mine stuck in the full position & never moved after 3 outings. When I pulled the pickup from the tank In had about 2 gallons in it. Lucky I have a 42 gal tank. I cleaned the sending unit with alcohol & 0000 steel wool & made sure it was working with a VOM meter on the ohm setting. It worked through the entire swing of the sending unit.
     
  6. Hoplite808

    Hoplite808 Well-Known Member

    345
    Jan 11, 2022
    Honolulu, HI
    1996 Sea Ray 270 Sundancer
    Mercruiser 7.4 LX MPI EFI (Gen. V)
    @55Trucker, find the sender on the top of the tank. There should be two wires. One is a ground, a constant negative connection to the battery, the other runs directly to the back of the gauge. The sender uses resistance on the ground connection to make the gauge read how full the tank is. The positive lead on the back of the gauge should go through the ignition circuit and provide a constant 12v+ to the other connection on the back of the gauge when the key is on.

    To test the wiring disconnect the two wires on the sender then connect them together temporarily. Turn on the key and the gauge should read full if the wiring is fine.

    To replace the sender either take the old one out and temporarily close the hole with some duct tape or something that will prevent fumes from building up in the boat and crud from getting into the tank and then take the old one to the nearest boat parts store and match it with the ones they have on the shelf or,

    Replace and upgrade the old one to a reed type sender. Like sold here:

    https://www.westmarine.com/moeller-reed-switch-sending-units-P006_180_003_537.html

    To get the right size measure the depth of the tank from the old sender mount hole. If the tank is 14” deep get the 13” sender. Basically just get the one that’s the closest smaller size than the depth of the tank. The reed type senders last almost forever too as all the electronics are sealed inside and don’t come in contact with fuel or other things that cause rust or other damage over time. Then reconnect the wires and you should be good to go for a long time to come.
     
  7. Nater Potater

    Nater Potater Well-Known Member GOLD Sponsor

    Oct 19, 2020
    Southwest Idaho
    1992 300DA Sundancer
    Twin Merc Alpha I Gen II I/O's with 5.7 V8's
    If the gauge drops to "Empty" with the key off, then it's most likely the sending unit (the more likely culprit). Once you pull the sender out, connect one DMM lead to the mounting flange, and the other to the center electrical contact. With the float up/full, you should see around 30 ohms, whereas down/empty should be around 240 ohms. I suspect you'll find a bad sender unit.
     
    techmitch likes this.
  8. Bill Curtis

    Bill Curtis Well-Known Member

    533
    Mar 24, 2022
    Ahoskie, NC
    '95 220 Overnighter
    454 Mag Bravo3
    Just about everything you need to know about standard gauge systems.
     

    Attached Files:

    Nater Potater likes this.
  9. 55Trucker

    55Trucker New Member

    17
    Aug 15, 2022
    Otisfield, ME
    1998 SeaRay 175 Bowrider with Mercruiser 3.0 and Aplha1 Gen 2 outdrive
    Mercruiser 3.0 and Aplha1 Gen 2 outdrive
    This is all great information. I will run the suggested tests this weekend, and report back. Thank you!
     
    KrazyKarl likes this.
  10. KrazyKarl

    KrazyKarl Member

    43
    Jun 26, 2022
    1999 190CC Sea Ray
    4.3L Alpha (190 PHP) MCM stern drive
    If you feel like doing this yourself this is how I fixed my gas level pickup.
    Disconnect your battery before you start.
    I located the opening for the gas tank level pickup & removed the nut in the middle & the small ground screw on the side. Don't do this with a full tank. Then lower the front of the boat so the gas in the tank will shift forward. Then unscrew the five screws holding the sensor. Be sure not to drop any of them because they need to go back in place, also note the position on the sensor because it will only go back in that way.
    [​IMG]

    After getting the sensor out (you may have to bend the wire a little to get it out of the tank) This is what it looks like in the down or empty position.
    [​IMG]

    To clean the resistor wires I used alcohol & 0000 steel wool to scrub the contacts clean.
    [​IMG]

    While cleaning be sure to clean the under side of this moving contact & make sure it is touching the small metal contacts.
    [​IMG]

    When testing the sensor it needs to check at about 30 ohms on the 10 scale on the low or empty side.
    [​IMG]

    The high or full side should check about 80 ohms on the 10 scale.
    [​IMG]

    When you reassemble the sensor in the tank be sure to put the screws through the rubber gasket first because the holes will only align one way. Then tighten to a just tight condition so don't over tighten them.
    Reinstall the wires the same places they were to start with.
    Be sure to run your blower long enough before turning the key on to check the gauge.
     
    Last edited: Sep 17, 2022
    Nater Potater likes this.
  11. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx 502 mag
    2005 Baja 242 islander 496
    502 mpi Bravo 1
    496 mag B1
    Nicely done
     
    KrazyKarl likes this.
  12. 55Trucker

    55Trucker New Member

    17
    Aug 15, 2022
    Otisfield, ME
    1998 SeaRay 175 Bowrider with Mercruiser 3.0 and Aplha1 Gen 2 outdrive
    Mercruiser 3.0 and Aplha1 Gen 2 outdrive
    Indeed. Very well done. Thank you.
     
    KrazyKarl likes this.
  13. Bill Curtis

    Bill Curtis Well-Known Member

    533
    Mar 24, 2022
    Ahoskie, NC
    '95 220 Overnighter
    454 Mag Bravo3
    Just a quick FYI. Do NOT use silicone sealer on the gasket. Gasoline eats silicone almost immediately. Use a sealer like permatex aviators gasket sealer.
     
    Nater Potater likes this.

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