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Old 07-06-2020, 11:14 AM   #1
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MS 400 Fuel Sender

I have a 2003 MS 400 with 2 fuel tanks. I have a switch on the lower helm that switches from lower to upper helm for the Faria gauge. When I bought the boat the gauge showed about 3/4 tank of fuel. I also have a dual Racor fuel filter setup with valves to switch from port to starboard tanks.
I found out that the engine was drawing from the starboard tank when the generator ran out of fuel and I found the crossover was closed. I traced the generator fuel line to the port tank. I opened the crossover and now the tank reading is a little below 1/2 tank so I suspect the gauge is reading from the sender in the starboard tank.
My question is about the tank sending unit. It appears each tank has a sender. I read on another post from another MS owner with a 36 that he had a similar issue while testing the senders. He installed a mechanical float gauge to check the level on the other tank.

Do any other 400 owners have this configuration?

I'm wondering what others have done.

I'd like to install a switch on the dual filter panel so I'm reading fuel levels from the tank I'm drawing from. Any suggestions?
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Old 07-06-2020, 04:45 PM   #2
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I believe that the gauge only reads from one tank, I never bothered to figure out which one as I leave the crossover open. The Racor with valves to select a tank that you have is probably an add-on from a previous owner or a factory custom option as I have not seen a 400 with that set-up. I wouldn't be surprised if both fuel tanks had the senders installed but I think only one of them was wired up to the helm gauge. I would guess it's possible to install a switch to select either gauge but I have not attempted to do so.
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Old 07-06-2020, 07:58 PM   #3
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Quote:
Originally Posted by garmstro55 View Post
I believe that the gauge only reads from one tank, I never bothered to figure out which one as I leave the crossover open. The Racor with valves to select a tank that you have is probably an add-on from a previous owner or a factory custom option as I have not seen a 400 with that set-up. I wouldn't be surprised if both fuel tanks had the senders installed but I think only one of them was wired up to the helm gauge. I would guess it's possible to install a switch to select either gauge but I have not attempted to do so.

Thanks for the response.
I believe the original purchaser had the dual Racor filters added either by Mainship of he had them installed shortly after purchase. Either way, I like the idea of being able to switch filters and I'm sure this can be done while the engine is running. I also suspect the senders are installed in both tanks but only wired to 1 tank, more than likely the starboard tank. I'll post what I finally decide to do once I find out the configuration.
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Old 07-06-2020, 08:23 PM   #4
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Yes, the sender is on the starboard tank. It is impossible to access without cutting an inspection plate in the floor of the cabinet under the sink.


There is a sender on my port tank, but Like Gary, I have not wired it up. I'd like to, I've just had other things get in the way. I've considered wiring a fuel gauge on that tank that is in the ER. It would be easier, and honestly, you don't really need to look at it all that often, once a day is plenty.
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Old 07-06-2020, 09:04 PM   #5
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Suggest you leave crossover valve open...except when fueling. Diesel fuel pump volume is greater than crossover capacity...so close and fill each tank, then reopen. You will also likely find diesel return line only goes to one tank. You pump much more fuel than you burn - automatic fuel polishing.
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Old 07-06-2020, 11:02 PM   #6
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I have posted on this topic several times, and if you search on my user name you will find plenty. To summarize, my 30 Pilot came equipped with two fuel tanks with a bottom-feed crossover line from which a tee to a single Racor fed my single Yanmar 6LPA. The fuel return was to port only, and the Faria cluster fuel gauge was connected to the port tank only, although there was a fuel level sender installed in the other tank as well. Some other 30 Pilot owners have told me their stbd tank was the one hooked up to the fuel gauge; so don't assume all 390/400 boats are the same.

I liked NONE of this.

It was simple to cut a four-inch access (after which nice looking access hole plates were installed) under the bench seating to access the fuel level senders. Both were bad and needed replacement (easily obtained from WEMA/KUS). All that was required to read either tank level on the Faria cluster was to run a single wire to a new selector switch (ON-OFF-ON) at the console, connect both tank level sender wires to its inputs and send its output to the Faria. While I was at it, I put a tee in the fuel tank crossover line where I added a valved sight gauge. Shut off either tank momentarily to read the actual level of the other.

There was a plugged fitting on the top of the stbd tank matching the place on the port tank where the return fuel went to it. A wye valve placed in the return line, a pipe-to-barb adapter to replace the plug in the stbd tank fitting, and a bit of fuel hose resulted in selectable fuel returns, just like it should have been in the first place. Adding a second Racor with valving to allow running either or both completed the fuel supply and return system mods.

In order to keep track of the Racors' filter status without having to raise the engine hatch to look at the vacuum gauges on the Racors, I added a tee in the fuel line between them and the engine from which I ran a shut-off valve (normally open) and small semi-rigid hose up to a vacuum gauge at the console. When vacuum rises over 5 inches of Hg, I switch to the other Racor (I normally operate on one), and change the clogging filter at the end of the day.

None of this required anything beyond pretty basic DIY skill, and the result is a highly flexible fuel management system which will give me no surprises and a level boat at all times.
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Old 08-22-2020, 02:25 PM   #7
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My 2004 Mainship 400 has the active fuel sender in the port tank. Not sure if it was originally that way but that the way it is now. The sender was bad. To test it I removed bolts an raised sender as far out of the thank as I could. Maybe 6 or 8 inches. I then bent a coat hanger to push the float down to the bottom of the sender and read the gauge. It read 3/4 full with the float pushed completely to the bottom. I was getting 100 ohms but should have been 240 or OL.
As the sending unit was pulled out partially I just started pulling down on the sender as it rested on the fuel return fitting. The fitting gave extra support. As I pulled down I would then pull out. Repeat until sender came out bent like a banana. See pic 1.
I then bought a Bosch unit part no FST7591 for $25. See pic 2.
The new Bosch unit comes in sections which enable you to install lower section then screw together middle section and finally the last section. Fit like a glove with no cutting holes in floor.
You have to measure your tank top to bottom inside measurement. Mine was 19 inches. Use the chart Bosch gives and you assemble the unit outside the tank. Once this was done I marked the 3 sections with a sharpie. Lossened the screws, slid in tank, aligned sharpie marks and retightened. Came out great.
Hope this helps someone. Click image for larger version

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Old 08-22-2020, 06:00 PM   #8
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The nice thing about the Pilot is the bench seating completely hides the access hole deck plates from view. The miracle was that there was room enough to remove and replace the sensors without bending.
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Old 08-22-2020, 09:06 PM   #9
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Quote:
Originally Posted by rgano View Post
The nice thing about the Pilot is the bench seating completely hides the access hole deck plates from view. The miracle was that there was room enough to remove and replace the sensors without bending.
No such luck on the 400. Access hole would be right in salon floor. There was originally a pull out couch. We tossed that when we bought the boat. Wife likes chairs instead.
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Old 08-23-2020, 11:41 AM   #10
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MS400 Fuel Sender

Quote:
Originally Posted by bill.kimbell View Post
Suggest you leave crossover valve open...except when fueling. Diesel fuel pump volume is greater than crossover capacity...so close and fill each tank, then reopen. You will also likely find diesel return line only goes to one tank. You pump much more fuel than you burn - automatic fuel polishing.

As I mentioned in my original post I have a dual Racor setup and after a closer inspection the filters have a double valve that allows to pull fuel from either tank. There is also a return valve. You select port draw and port return and vice versa.

I did end up leaving the crossover open and plan on changing which tank fuel is pulled from each time I go out.

Interestingly enough that when I purchased the boat the engine was drawing from the starboard tank and that filter bowl was full of dark colored debris. When I changed the filters I opened the drain and had to use a small screwdriver to dislodge the debris to drain the bowl. I don't believe the filter was restricted as there is also a vacuum gauge connected to the filters and it read 0. I agree that the engine returns more fuel than it burns and switching tanks will help keep the fuel clean.
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Old 08-23-2020, 11:43 AM   #11
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Quote:
Originally Posted by Pmcsurf1 View Post
My 2004 Mainship 400 has the active fuel sender in the port tank. Not sure if it was originally that way but that the way it is now. The sender was bad. To test it I removed bolts an raised sender as far out of the thank as I could. Maybe 6 or 8 inches. I then bent a coat hanger to push the float down to the bottom of the sender and read the gauge. It read 3/4 full with the float pushed completely to the bottom. I was getting 100 ohms but should have been 240 or OL.
As the sending unit was pulled out partially I just started pulling down on the sender as it rested on the fuel return fitting. The fitting gave extra support. As I pulled down I would then pull out. Repeat until sender came out bent like a banana. See pic 1.
I then bought a Bosch unit part no FST7591 for $25. See pic 2.
The new Bosch unit comes in sections which enable you to install lower section then screw together middle section and finally the last section. Fit like a glove with no cutting holes in floor.
You have to measure your tank top to bottom inside measurement. Mine was 19 inches. Use the chart Bosch gives and you assemble the unit outside the tank. Once this was done I marked the 3 sections with a sharpie. Lossened the screws, slid in tank, aligned sharpie marks and retightened. Came out great.
Hope this helps someone. Attachment 106906Attachment 106907

Pmcsurf1

Thanks for the great post. If I ever have a sender issue, I'll follow your lead.
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