2010 R29 main tank auto siphoning into auxiliary tank

[Mattatoar]

Long story, short version: I discovered diesel has been leaving the main/forward tank and filling the rear/auxiliary/Wallas heater tank (that’s not working). My assumption is when the bow goes up the fuel flows by gravity back to the auxiliary. The Johnson fuel pump does not have a back flow prevention valve or what not. It does pump from auxiliary to main.

So…. install a simple valve in the fuel line or a backflow valve? Install a new pump that has a backflow prevention system (if exists)?

 

[fishheadbarandgrill]

Keep your selector switch in the off or generator position when not transfering fuel. That should stop any siphoning back to the aux fuel tank.

 

[Mattatoar]

Are you referring to this switch? I was informed it is disabled and no longer a switch between shore power / generator / whatever.
My fuel pump that feeds from the auxiliary tank is on a rocker switch right next to the pump under the starboard hinged step area. I’ve used it. You have to hold it to pump. I had the tank 50% emptied into the main and then it was full again after a trip out.
I still don’t have a grasp of what switches are inert, repurposed, or as expected. Clearly some modifications have been done since 2010. This whole boat is different from any boat I’ve ever owned before.