2002 Mainship 390 - fuel tank sensor

[Lshulan]

It seems like my fuel tank sensor is not working properly, it does register full when it is actually full, slowly drops down to 3/4 which is fairly accurate, but then doesn’t move down as fuel is consumed. It was a hair below 3/4 when I filled with 225 gallons which should have shown about 1/4. I monitor hours and have a pretty good idea based on PO detailed fuel burn results of what I have burned but it would be nice to have a working gage. Anyway, has anyone serviced or replaced the sender on the STBD tank on a MS 390? What can I expect? Anything special to know ahead of time?

 

[Shrew]

I wouldn't bother servicing it, I'd just replace it.

 

[Lshulan]

Shrew - thanks but if it’s something simple, why replace? Anyway, my main question would be on the MS390, is the sender easily accessible (where is it? - I’m not on the boat, trying to think thru what to do) and how to remove it?

 

[ralphcramden]

hi. don't you have unit below and upper Station? both display incorrectly? I have a MS40.

 

[Lshulan]

Both upper and lower have same readings, that’s why I’m pretty sure the sending unit is at fault. I’m looking for someone with a MS390 to let me know about changing out or cleaning the sending unit, what’s involved

 

[Shrew]

Shrew - thanks but if it’s something simple, why replace? Anyway, my main question would be on the MS390, is the sender easily accessible (where is it? - I’m not on the boat, trying to think thru what to do) and how to remove it?

It's on the top of the tank. All the ports on my tanks are on the top about mid tank. Go into the engine compartment and mine are on the inboard side of the tank by the bulkhead beneath the sliding door. The sender will be the port with wires instead of a fuel hose.

I've never heard of 'repairing' a sender. They go bad. It's either the float is saturated, parts aren't moving freely, or there is corrosion in the electrical portion.

It's also one of those parts that to remove, fix and reinstall is more work than just remove and replace. They are roughly $50. For $50, I'm going to replace both at the same time and not even look back for 20 more years.

 

[Cold Duck]

West Marine has a generic sender that I used to replace the port sender. Very easy, can't remember the price but under $50 sounds right. Not worth trying to repair unit if it's bad. Only issue I had with port sender is it is under the step and impossible to remove (no head room). But there was a second unused hole capped off so I used that instead. Stbd was easy. They put tanks in before deck and both tanks have sender about the same spot in tank. Noone thought that the port unit might not be accessible once deck installed. Poor engineering on that one.

 

[tiz]

I’d be a bit surprised if you can get the senders out give that the tanks are under the salon floor and deck without a lot of clearance overhead. Agree with others, just plan to replace if you can get them out. Before installing, make sure the new sender works with your gauges.

—Kevin
2001 MS 390 ‘Petrel’

 

[Lshulan]

If there isn’t room to get the sender out, how do you replace them? Anyone with a MS390 have actual experience in getting the sender out? It’s my understanding that there is only a sender on the STBD tank because of the crossover pipe, ostensibly the two tanks should be more or less the same level

 

[tiz]

Would love to know that. Just in case ....

--kevin

2001 390 'Petrel'

 

[Cold Duck]

My boat is a 350, There's enough room (just barely) to get the sender out on Stbd tank. The placement of the Port sender on my boat is such it cannot come out but further forward there is room and I had a spare hole and cover in the tank that I used. So in the port tank I have the new and old senders.

 

[Dougcole]

I have the same issue on my 400, the port side sender is barely accessible and is not hooked up to anything. The Starboard side is completely inaccessible and wired in but is no longer functioning. I am planning on putting in an access plate through the cabin floor under the galley drawers to reach the Starboard side, it won't be visible after it is installed and the drawers are back in. It will make the next change out much easier.



The tank cleaning guy I work with recommended that I go with a different brand of sender, I think it is a Wema (?) which is not compatible with my current gauges. He said the Wema senders are electronic and MUCH more reliable. He recommended mounting new gauges in the ER and not worrying about the gauges at the helm. I like that idea as I have no need to check the fuel constantly at the helm. Checking it during routine daily engine checks is plenty often.



Not sure what to do about the port side. I may just leave the old one in place and just estimate fuel burn based on the Starboard side. Problem is though that the gen-set pulls from the port. Mainship really didn't do their owners any favors by configuring the tanks this way.

 

[Deckape]

No sight tubes on the Mainships ?

 

[Shrew]

It’s my understanding that there is only a sender on the STBD tank because of the crossover pipe, ostensibly the two tanks should be more or less the same level

I have a sender in each tank and a single gauge. I have switches that set the senders to either the upper or lower helm. When at the active helm, I have a switch that changes the gauge to read from port or Stbd. I wouldn't trust the crossover to keep the tanks balanced. Mine can get as much as a 1/3 of a tank in difference.

The generator pulls from only one tank. If there is a little bit of a list, the high side tank will start filing the low side tank.

 

[Cold Duck]

I have a sender in each tank and a single gauge. I have switches that set the senders to either the upper or lower helm. When at the active helm, I have a switch that changes the gauge to read from port or Stbd. I wouldn't trust the crossover to keep the tanks balanced. Mine can get as much as a 1/3 of a tank in difference.

The generator pulls from only one tank. If there is a little bit of a list, the high side tank will start filing the low side tank.

My '97 MS350 is identical to this with similar out of level tank issues. I actually am shutting stbd tank off and running just off port to keep boat level. Cross over doesn't keep boat level. Tanks may be level but as boat lists to port, stbd tank empties to port and never levels out the boat. I think all 350s/390s list to port. Any 350s/390s out there without listing?

 

[Derek]

No sight tubes on the Mainships ?

Of the 2 I have had…Oh I wish they did.

 

[swboater]

I have a 79 Mainship.Same problem with no sight tubes. I use a infrared temp. sensor to find fuel level on mine.Works very well.

 

[Cold Duck]

I have a 79 Mainship.Same problem with no sight tubes. I use a infrared temp. sensor to find fuel level on mine.Works very well.

Like this idea, never thought of it. Have the ir temp sensor aboard already.

 

[Lshulan]

Swboater - that’s a great idea but I’d still like to be able to read a fuel gage without having crawl down into engine compartment. But it would be handy as a backup for sure.

But for anyone with a 350/390 in the 2002 range or thereabouts, is there access to top of the stbd tank to get the sensor out for replacement?

 

[Derek]

I have a 79 Mainship.Same problem with no sight tubes. I use a infrared temp. sensor to find fuel level on mine.Works very well.

Brilliant idea!

 

[gerilla]

I have a 79 Mainship.Same problem with no sight tubes. I use a infrared temp. sensor to find fuel level on mine.Works very well.

Does the IR method work with cold engines or does the engines have to have been running and returning warm unused fuel back to the tank? What kind of temp differential do you see between the two areas? Thanks.