MS 390 - Fuel sending unit(s)

[Lshulan]

My upper and lower fuel gages are not working very well, both stop showing anything below about 3/4 full. My mechanic was looking at the fuel sending units and said that both tanks had sensors and that there must be a switch to select which tank. I explained that the only switch I knew about was to toggle between upper and lower helms. He insisted that there was wiring from both tanks and therefore must be a switch. Anyone with a 350/390 know anything about this. Related issue, he said that the fuel gages could be either European controls or American and that the new senders had to match up. I would suspect American of course but does anyone known anything about this? I have a thermal sensor to ping the sides of the tanks and of course can keep track via engine hours but it would be nice to have reliable gages.

 

[tiz]

My upper and lower fuel gages are not working very well, both stop showing anything below about 3/4 full. My mechanic was looking at the fuel sending units and said that both tanks had sensors and that there must be a switch to select which tank. I explained that the only switch I knew about was to toggle between upper and lower helms. He insisted that there was wiring from both tanks and therefore must be a switch. Anyone with a 350/390 know anything about this. Related issue, he said that the fuel gages could be either European controls or American and that the new senders had to match up. I would suspect American of course but does anyone known anything about this? I have a thermal sensor to ping the sides of the tanks and of course can keep track via engine hours but it would be nice to have reliable gages.

We have a 2000 390. I know of no switch to select port/stbd tank for gauging. Just the upper/lower as you mentioned.

 

[J.T kearney]

Lshulan, my 98 350 has a port or starboard tank switch because there's only one gauge at the helm stations. There's also and upper and lower switch at both stations. Currently non operational but on my to do list. Will be using a heat temp gun for now.

 

[ranger58sb]

My upper and lower fuel gages are not working very well, both stop showing anything below about 3/4 full. My mechanic was looking at the fuel sending units and said that both tanks had sensors and that there must be a switch to select which tank. I explained that the only switch I knew about was to toggle between upper and lower helms. He insisted that there was wiring from both tanks and therefore must be a switch. Anyone with a 350/390 know anything about this. Related issue, he said that the fuel gages could be either European controls or American and that the new senders had to match up. I would suspect American of course but does anyone known anything about this? I have a thermal sensor to ping the sides of the tanks and of course can keep track via engine hours but it would be nice to have reliable gages.

There are display/sensor combos meant for single and dual helm installations. I think different resistance curves. In the literature, I've not ever seen a mandatory switch mentioned for the latter. OTOH, if you have the former, maybe a switch would have been used for that. Doesn't sound like your issue, anyway...

Do you have a separate display for each tank and each station? If so, I'd guess that argues for no switch required. OTOH, if you only have one display at each station... that suggests you'd need a way to select which you'd want to view. Unless both tanks are conceptually strapped together into one big tank?

Might help to track down your display and sensor part numbers. Also might be you have an swing-arm style fuel level sender, which is a pretty goofy looking contraption... and the float arm sometimes eventually decides to do it's own thing. These are easily replaced by a straight tube/float version such as what KUS (was WEMA) offers. Latter work like champ, easy fix.

I've often seen mention of U.S versus European resistance versions. Ours is said to typically be 33-240 Ohms, with 33 being "full' and 240 being "empty." Euro is typically said to be 10-180 Ohms, and I think maybe 180 is "full" and 10 is "empty" (not sure about that last, can't quite see how that would work.) You could test one of your displays to sort that out.

-Chris

 

[Cold Duck]

Looks like there are different configurations maybe upgrade? My 97 350 has single guage in upper station only with a single toggle switch to select Port or Stbd to the single guage. Nothing at the lower station, no guage, no switch. One sender went bad, replaced with a generic sender at West Marine. Worki

 

[Shrew]

My 99 350 has two switches at the upper helm. One selects the upper or lower helm. The other selects the Port or Starboard tank. At the lower helm, there is a single switch for port or stbd tanks.

Why they chose to put the helm selector at the UPPER, I will never know.

 

[J.T kearney]

Looks like there are different configurations maybe upgrade? My 97 350 has single guage in upper station only with a single toggle switch to select Port or Stbd to the single guage. Nothing at the lower station, no guage, no switch. One sender went bad, replaced with a generic sender at West Marine. Worki

C Duck, how much room did you have above the tank to install the sending unit ? I've got about 2 to 3 inches below the port side steps directly above the sending unit
Cheers J.T.