View Full Version : fuel tank sending unit.
09-15-2009, 08:57 AM
I am experiencing a problem with my 2005 390MY diesel. The port gauge and smart craft monitor shows a huge difference in the fuel level compared to the starboard tank. I am assuming both of these gauges use the same sending unit. Last night the starboard tank gauge showed 65 gallons while the port tank gauge showed less than 10 gals. remaining. While I thought that both tanks had approx. 65 gals. left, it makes me a little nervous. After running the boat for 20 minutes the port tank registered 47 gals. I have noticed a difference in levels no matter if the tanks are full or not. Again, my guess is the sender unit. Perhaps others have experienced this problem and can reaffirm my assumption before I replace the sending unit.
09-15-2009, 10:52 AM
I have a similiar proble with my fuel guages. I now ignore them, always fill the tanks and keep track of the burn rate per hour and therefore I know how much is left. My tanks have a cross over so I know that they are balanced. Without a cross over it becomes more difficult but it can be done by computing burn rate for each engine. Knowing the burn rate also helps to detect if something is going wrong with the engines, when I started having problems with my turbos, my burn rate went up 4 gallons per hour.
09-15-2009, 07:33 PM
I had the same problem on my 05 340. The mechanic told me to recalibrate my smartcraft and now everything seems to be fine.
09-15-2009, 10:06 PM
Some Merritt Island boats had fuel senders that were over tightened in the tank. That bent the plate that fit on the tank surface and affected the resistance the sender sends to the gauges. The result is really screwy fuel gauge readings. I don't know that this is your problem, but it is worth a look at the sender on top of the tank to see if the round plate with 5 or 6 screws in it is perfectly flat.
09-17-2009, 03:28 PM
Thanks for the responses. I'll check that the sending unit is lying flat. As far as recalibrating the Smart gauge, I looked this morning and both tanks read virtually the same level. When I do experience the problem with the port fuel tank, both the indash analog and the Smart gauge show similar readings. That makes me think both gauges use the same sending unit on the port tank. I do know that it is kind of nerve racking when I operate below half a tank only to see the port tank gauge fall to 3 gal. remaining when my starboard tank registers 3/8 of a tank.
09-20-2009, 08:32 PM
I checked out the sending unit and it looks flat to me. This is the first time this problem has happened and since the boat is 2005 I would think I would have experienced it previously if there was an installation problem. There is only about 3"-4" inches of room above the tank and I would expect a problem removing it. I hope the unit doesn't have a long rod and arm float like an automotive style. No way is there room to remove a unit like that. Does anyone have any experience in removing the sending unit? The sending unit is for a 150 gal rectangular tank. It also has what looks like a 3 or 4 wire weatherproof connector about a foot from the unit.
09-20-2009, 10:24 PM
Sometimes the engineers place an access plate right above the sender, other times they do not. The problem is usually not that there is no access, but that you have to literally tear the cockpit apart to get access to the spot above the tank to saw a hole and to remove a 24"-30" long sender. Installing an access port is a 5 minute job with a hole saw and a $5 part.........if you can get to the spot you need to with a drill.
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