1985 M 39 DC gas tank selector

Things that are of general interest.
kimbo
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Location: Michigan

1985 M 39 DC gas tank selector

Postby kimbo » Mon Jul 29, 2019 4:34 pm

Hello All,

Still learning the system of my M39DC. When fueling up I always have equal amounts of gas into both tanks. I noticed that the port tank is reading 3/4 full and the starboard tank is 1/16 full or less yesterday. The tank under the bed looks like one big tank but with two opening for gas on deck I would assume two tanks below. I can tell the boat has a slight list to port I am assuming from the port gas tank. There are three gas valves in the engine compartment with all three inline and open. So, question is to my fellow Big M's, what am I missing? Does the port tank free flow to the starboard? Could the fuel pickup in the port tank be faulty or some other item that I am missing? Thanks in advance. Photo of gas valve is hopefully attached.

Kim
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Harryb
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Re: 1985 M 39 DC gas tank selector

Postby Harryb » Mon Jul 29, 2019 4:57 pm

From the picture it shows you have selected to fuel any engine from any tank.I run mine with the middle valve closed so as to run fuel from port tank to port engine and starboard to starboard only
1987 32 f/b sedan with twin 318's Docked on florida's nature coast

jralbert
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Re: 1985 M 39 DC gas tank selector

Postby jralbert » Mon Jul 29, 2019 9:18 pm

I was going to say the same thing.

Another factor at play here might be that the engines are burning fuel at different rates - that would account for fuel gauge differences.

Also, list may be due to water tank - is it on the port side? At 8lbs / gal times x gals, that could be weighty enough to cause a little list.
-joel-
former owner 1988 '32 FB Sedan
Chesapeake Bay
twin 318 / 240 hp
Potomac MD

kimbo
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Joined: Mon Oct 09, 2017 12:44 pm
Location: Michigan

Re: 1985 M 39 DC gas tank selector

Postby kimbo » Tue Jul 30, 2019 6:31 am

My fear is that the pickup on the port tank is not working and if I ignore this fat dumb and happy, I might run out of gas. I also thought there might be some other valving or tank selector that I was unaware of at the helm. Guess my next trouble shooting project will be to close the starboard valve, start her up and see what happens.

Thanks for your replies,

Kim

SunbeamIV
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Re: 1985 M 39 DC gas tank selector

Postby SunbeamIV » Tue Jul 30, 2019 8:36 am

On my 32, I noticed that the generator can only take suction on the starboard tank. That would also explain the tanks not going down evenly.
Scott, 32' 1989 sedan flybridge
Located: Edgewater Yacht Club
Lake Erie

Fastjeff
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Re: 1985 M 39 DC gas tank selector

Postby Fastjeff » Tue Jul 30, 2019 10:12 am

In RVs, the intake pipe for the generator is higher in the tank so the generator ruins out of gas long before the truck does.

Could that be related to this issue?

Jeff
"We live at the bottom of an ocean of air, not at the top." General Marvage Slatington

Harryb
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Re: 1985 M 39 DC gas tank selector

Postby Harryb » Tue Jul 30, 2019 3:34 pm

More than likely different resistance in the port and starboard supply lines resulted in the one side being favored. Now you have to find out why. There"s been lots of posts on here about cleaning the tanks and anti-siphon valves and servicing the water separators.
1987 32 f/b sedan with twin 318's Docked on florida's nature coast