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Old 07-18-2019, 03:28 PM   #1
MD3
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Seneca fueling question

2018 Seneca with the fuel tanks on both sides.....

When filling up at a regular gas station (not a truck stop) and filling one side at a time it.....does it make a difference which side I fill first ?

Last weekend I filled the passenger tank to the brim, moved coach around the pump to fill driver's side and the passenger side was now down considerably. The passenger tank obviously leveled to the driver's tank...

How do I get both tanks full if I can only fill one side at a time ?
Any tricks to topping off both tanks when filling them one at a time ?


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Old 07-18-2019, 04:01 PM   #2
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the drivers side is primary, because it will use its fuel first and the pass side will transfer fuel to drivers side. the drivers side has the fuel pump that supplies fuel to the eng
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Old 07-18-2019, 04:38 PM   #3
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I realize this doesnít answer your question, but unless itís a dire need, I only fill at truck stops, and, Iíd highly recommend the tank fill extensions, worth the money.
- easy access to fill both tanks
- fresh diesel
- join all the driver programs, download the apps, and use mobile fueling when available - huge time saver.
- and, truck stops have everything a Seneca driver would need.

Safe travels.
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Old 07-18-2019, 05:37 PM   #4
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Truck stops are the easiest however I live 60 miles from the closest dual pump station so i have to move the unit to fill both sides.

Get the extensions. They make fueling much easier.

I fill as much fuel as I can on the first side and then move as quick as I can to the other side. Try to run the engine as little as possible as this really moves a lot of fuel. Once the second side is full I let it set for a minute or two. Then top off. Usually can fit another gallon or two as it is leveling out. The tanks are connected via the fuel pickup lines and the return lines from the supply pump. With the engine off the tanks self level at around a gallon or so a minute. With the engine running it is increased significantly.

I have tried to reduce the pressure build up in the opposite tank by removing the cap on that tank. This does seem to increase the self leveling rate as the siphoning effect is not fighting the air pressure in the cap vent. But in the end it really was not worth it.
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Old 07-18-2019, 06:26 PM   #5
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I have the fuel extensions. Good stuff.
Truckstop is ideal but very far away so not worth driving to the truck stop just to fuel up.

Just wondering if anyone knew any easy tricks to get more fuel on board at a single-sided pump. I can save over a $1 a gallon in AZ before coming back into CA and I want to top off as much as possible.


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Old 07-18-2019, 09:18 PM   #6
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I wish that you could get both tanks full but as far as I know only a truck stop with satellite pump can completely fill both tanks & the “ Extend a fill “ is AMAZING Les
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Old 07-19-2019, 05:00 AM   #7
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Question, I don't have a dual tanks on our Greyhawk but doing a little reading i see that the Seneca has a constant supply and return line. the supply comes from the drivers side and the return goes to the passenger side. One would think if you left the truck running while filling the unit would self level would it not?
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Old 07-19-2019, 06:06 AM   #8
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Quote:
Originally Posted by Berjr View Post
Question, I don't have a dual tanks on our Greyhawk but doing a little reading i see that the Seneca has a constant supply and return line. the supply comes from the drivers side and the return goes to the passenger side. One would think if you left the truck running while filling the unit would self level would it not?
The dual tank Senecas have a supply and return line to each fuel tank. The fuel level sender is in the driver side tank and the generator does draw and return only to the driver side tank. The leveling is accomplished the Equiflo system common to many trucks with saddle tanks today since the larger crossover lines connection the bottom of fuel tanks (common in the past) have fallen out of favor due to potential damage and huge fuel spills if damaged. And to correct another misconception - there is not a fuel pump in either tank, the pumps are on the chassis engine and one on the generator for itself.

Another Seneca owner has a website where the Equiflo system is explained here:
Jayco Seneca Freightliner M2 Two Separate Fuel Tanks and Equiflo, How the hell does this work? | RV Underground

I also have attached some technical documents about the system itself and a picture of my fuel suction/return lines coming out of/back into my tanks.
Attached Thumbnails
Fuel line picture.jpg  
Attached Files
File Type: pdf Fuel transfer system.pdf (17.4 KB, 8 views)
File Type: pdf Fuel transfer system 2.pdf (143.1 KB, 5 views)
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Old 07-19-2019, 07:02 AM   #9
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thanks Robbie my miss understanding. My old pickup had 2 tanks and i always filled front tank first then rear tank and never had issues, but the rear tank siphoned to front as that is where the pump was. Diesel truck is different, it appears and from what i gather they have a constant flow of fuel rotation that i am not up to full knowledge on.
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Old 07-19-2019, 08:19 AM   #10
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what are the extensions and where can you get them
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