I have a 2017 Sundancer 400, and...

[lady_Patricia]

I have a 2017 Sundancer 400, and I am puzzled.

In the spring, I left the diesel tanks full, the electronic gauge indicated 98% each side, which is normal when I have full tanks. Whenever I fill up, I have my wife watch the gauge as I fill the starboard side, and to let me know when it reaches 98%, I stop pumping there, and move to the port side. Usually, it takes about the same amount of fuel in both tanks.

Since we got back down to Florida in Sep. we have made a few trips and put about 12 hours on each engine, and because it has been so hot, we have also put about 12 hours on the generator. Because the generator pulls from the starboard tank (according to the manual), I would have expected the starboard tank to be lower than the port. But when I headed out this morning, the gauges indicated that I had about 67% in both tanks. I was scratching my head about this, when it because more puzzling. I started to fill the starboard tank and my wife was calling out the percentage fill, but she also said the port tank was going up. My thought was that she was getting a false reading on the port tank due to weight distribution, but the starboard side took 65 gallons when it read 98%, and the port side read about 85%. I switched over it fill the port side and it took 10 gallons then overflowed.

Clearly, fuel is somehow transferring from one side to the other, and I don't understand how this can happen. I did not buy the fuel transfer pump, and I am pretty sure that this was not happening last year. Anyone know what is going on?

[Naut_Home]

I have a 2016 400 Fly, basically the same boat. The first time I filled up I moved from one tank to the other thinking that they were independent. They are not, fuel self balances and I now fill whichever side I am tied up to on the fuel dock.

[lady_Patricia]

One would wonder why they sell a fuel transfer pump if the tanks self level??????

[Naut_Home]

I find that engaging the transfer pump makes the balancing occur a bit quicker, but at the end of the day, it’s not really necessary

[BWLW]

I have an older (2005) sundancer and it came from the factory with fuel lines hooked up incorrectly. Diesel engines run fuel continuously with unused fuel returning to the tank. On mine the return fuel for both engines went to the same tank. So one engine appeared to use little fuel and the other a lot. Might check this - let searay do this.

[GenSpi]

Check your fuel transfer levers. It appears that your generator is pulling from the starboard tank and returning fuel to the port tank. The fuel being pulled from the Starboard tank should return to the starboard tank. This is a common situation if the levers are not set correctly.

[lady_Patricia]

There are no fuel levers on the 2016/17 Sundancer 400.

[GenSpi]

I have a 08 48 SD. Didn’t know that. Too bad as it would have been a simple fix!

[Captain_Rusty_H]

Your new 400 Sundancer does have a cross over pipe which allows fuel to travel from one tank to the other. For more details and a few engineering drawings to show the details, please contact me at Sea Ray Boats in Fl....have trouble finding me, I will find you!..Rusty Higgins

[lady_Patricia]

I would love to have more understanding of how the tanks work. My phone number is 941 639 3577

[lady_Patricia]

Captain Rusty Higgins. While I wait for your call, I have two questions. Why is this fuel crossover not mentioned in the manual? Why offer a fuel transfer pump, if the fuel crosses over all on its own?

[Captdkw]

The connection between the tanks is made at the top of the tanks. So they do NOT self level nesesatating a fuel transfer pump.

[lady_Patricia]

Captdkw: Thing is, they do self level. In fact I only have to fill one side, and the other tank fills up. My theory is that the transfer connection became full of fuel and is now acting as a siphon. I think if I empty the tanks down to below the crossover pick up level, the self leveling will stop.

[Captdkw]

Each separate tank is filled via a 1-1/2” hose, port and Stbd. There is a 1-1/2” crossover at the TOP of the tank that allows you to fill the other tank once the tank you are filling is full. So yes they are self leveling WHILE FILLING. In use there are separate fuel pick ups for each motor. Your gen set burns very little fuel compared to the big diesels so its fuel use is hardly noticeable. The only way they could be self leveling IN USE is if there was a connecting hose at the bottom of the tank. But they don’t do that because of ABYC standards and rules. (Imagine a fuel leak in that hose at the bottom of the tanks draining both fuel tanks into the bilge!) Because the tanks ARE NOT joined at the bottom you need a fuel transfer pump to level the fuel if say for instance you ran one motor and not the other or you ran the gen set for days and it lowered one side creating a hull list. The transfer pump is an unlikely as a huge siphon source as the fuel must get past several impeller vanes to move from one tank to the other.

[lady_Patricia]

Captdkw: When filling, it is not the case that one tank fills, and then the other. They fill simultaneously, if they are both at a quarter before filling, if I bring the starboard up to 50%, the port will come up to 50% at the same time. I don't have a fuel transfer pump, that is why I think that the fuel is siphoning from one tank to the other via the crossover tube. This would also explain why the tanks self level while underway.

[Captdkw]

Ok. Maybe there's a difference between the 400 fuel tank system and our 460 fuel tank system. If you can see the fuel tanks I would look for some connection near the bottom that allows simultaneous filling. I know big yachts do this because the fuel fills (and engine rooms) are midship so you can fill both side from one fill location. So your not dragging hoses around boats or having to turn the boat around to fill the other side. Bottom line is on my boat with two fills at the stern I fill each independently. But as a safety one tank will "overflow" into the other tank before overflowing overboard.

[CPIGUY]

I recently took delivery of a brand new 2017 460DA. I will be filling it up for the first time later this week. I was curious what the conclusion was for how the tanks fill on the 460.

[lady_Patricia]

The engineers at Sea Ray are still scratching their heads. So far, no one has come up with an answer.

[Captdkw]

Congratulations cpiguy on your new boat. I still stand by my comments in this thread. I own a 2017 460 FLY with Cummins and conventional shafts. I’ve put 550 hours on the boat at avg fuel consumption of 44 gals/hour. So I have put thousands a gals ( approximately 24,000 gals) of fuel into this boat. The boat has a total fuel capacity of 375 gals divided between two tanks. The tanks are joined at the top by a 1-1/2” hose that is only about a foot long. Otherwise they are separate tanks. The fuel fills are mounted high on the decks at the transom. (Higher than the tanks). When filling you will fill one side. I usually watch the fuel gauge until 95% full and stop there. Then I fill the other side. If your using hi speed pumps you need to be careful because you will burp out the vent and fill pipe when full. That’s why I stop at 95% full and not 100%. If your not using high speed (<20/gal/min) you can actually fill the other tank from the same fill because of the cross over at the top of the tank. But doing it this way it’s easy to burp from the vent so I don’t suggest it.
Climb down between the engines and look at the tanks and their connections. I also have an electric transfer pump but rarely use it. The tanks draw down pretty evenly even with the gen set drawing from the port tank ( gen set burns very little fuel. Less that 5 gals/hour.) Your owners manual should have a drawing on tank configuration. Good Luck!

[CPIGUY]

Yes, I have the schematic of the tank, and what you say is definitely accurate. I also have the fuel transfer pump, which I don't think will ever get used. I've used 3/4 of my tanks, and they're both showing a balance of 140 gallons. I've run the gen set every time I've run the engines. Interesting that it hasn't had any noticeable impact on the balance between the 2 tanks. This is not the largest boat I've owned, but it is my favorite!

[lady_Patricia]

Problem solved, I traded the 400 in on a brand new 460 with a fuel transfer pump.

[CPIGUY]

Congratulations! I love my 460. First trip real voyage is next weekend. Can’t wait! Where are you located?

[lady_Patricia]

Punta Gorda, Fl. You?

[CPIGUY]

Channel Islands, California. Did you get Zeus drives or shaft? Which entertainment system?

[lady_Patricia]

I went with the V-Drive, not a big fan of Zeus. Too expensive to maintain and repair if you happen to hit something. Just the standard entertainment system, with fore-deck speakers, and the extra TV etc in the forward stateroom.

[CPIGUY]

Use her in the best of health!

[Captdkw]

Congratulations Lady Patricia on you move up to the 460 Sea Ray. Enjoy your boat. Welcome to “460 club”. We are located in North Palm Beach