Journey with Confidence RV GPS App RV Trip Planner RV LIFE Campground Reviews RV Maintenance Take a Speed Test Free 7 Day Trial ×
Jayco RV Owners Forum
 


Reply
 
Thread Tools Search this Thread Display Modes
 
Old 09-23-2022, 07:53 AM   #1
Junior Member
 
Join Date: Apr 2019
Location: Golden
Posts: 8
Question 2018 Seneca w/ 2 Fuel Tanks - Question

I need help understanding how the two fuel tanks work, dispense fuel, and report the fuel levels on the instrument panel fuel gage. It's driving me CRAZY!

For starters, this is a horrible design that was fixed when the late model 2018's were released. But that does me little good.

I don't know if all the fuel comes out of one tank before the other is used, or if the fuel comes out of the tanks at the same time. My fuel gage will report empty when I know I've got at least 20 or 30 gallons remaining, but I'm not sure which side has fuel and which is low. Then I have to guess at how many miles I have left before I run out.

Has anyone figured this out???
EGChester is offline   Reply With Quote
Old 09-23-2022, 08:12 AM   #2
Senior Member
 
TWP723's Avatar
 
Join Date: Mar 2015
Location: Abingdon
Posts: 5,967
Fuel is pulled from one tank until empty and a FPDM (fuel pump driver module) which is controlled by the PCM and located on the frame, switches the system to the other tank. Each tank has it's own pump and sender for the gauge. At least, that's how it leaves the factory. Now, if yours is still set up this way..I don't know.
__________________
2013 Jayco Eagle 328 RLTS
2021 Keystone Montana 3121RL
2013 F350 6.7L 4x4 CCLB
W/Air Lift air bags (front & rear)
Equal-I-Zerô WDH & B&W Companion
TWP723 is offline   Reply With Quote
Old 09-23-2022, 08:16 AM   #3
Senior Member
 
TWP723's Avatar
 
Join Date: Mar 2015
Location: Abingdon
Posts: 5,967
Years ago, they didn't have driver modules. Instead, they used a switching valve on the frame that would switch tanks over. But it was done manually with a tank switch on the dash.
__________________
2013 Jayco Eagle 328 RLTS
2021 Keystone Montana 3121RL
2013 F350 6.7L 4x4 CCLB
W/Air Lift air bags (front & rear)
Equal-I-Zerô WDH & B&W Companion
TWP723 is offline   Reply With Quote
Old 09-23-2022, 09:16 AM   #4
Lost in the Woods
 
Join Date: Apr 2022
Location: Plano
Posts: 543
Things have come a long way from my '59 VW Van, didn't have a fuel gauge, when it started sputtering you pulled a cable under the drivers seat which released a one gallon reserve into the fuel tank. You then had another 40 miles or so to borrow a dollar from a friend so you could drive around another week.
Onyrlef is offline   Reply With Quote
Old 09-23-2022, 12:14 PM   #5
Senior Member
 
Robbbyr's Avatar
 
Join Date: Dec 2014
Location: Akron
Posts: 3,029
Quote:
Originally Posted by EGChester View Post
I need help understanding how the two fuel tanks work, dispense fuel, and report the fuel levels on the instrument panel fuel gage. It's driving me CRAZY!

For starters, this is a horrible design that was fixed when the late model 2018's were released. But that does me little good.

I don't know if all the fuel comes out of one tank before the other is used, or if the fuel comes out of the tanks at the same time. My fuel gage will report empty when I know I've got at least 20 or 30 gallons remaining, but I'm not sure which side has fuel and which is low. Then I have to guess at how many miles I have left before I run out.

Has anyone figured this out???
There are no in-tank fuel pumps on a Freightliner Seneca. The chassis uses an Equiflo system, common on big rigs to equalize the tanks since crossover lines were discontinued years ago. The fuel level sending unit is in the driver's side tank. Only one sending unit. The generator pickup and return lines are also in the driver's side tank. The fuel senders are known to be horribly innacurate. Some folks even had new ones installed with no improvement.

The old-style crossover line was effective, but subject to damage from road debris. One road alligator attack could dump a hundred gallons or more of diesel fuel into the environment in minutes.

Here is a Seneca owner's simple explanation of Equiflo, there also are very complicated ones if you go digging. The only problem I ever heard a Seneca having was uneven fuel levels side to side, the owner found that insects had blocked one of the fuel tank's vent tube. The vents come off the top of the tanks and then come down the sides of the tanks towards the center of the rig. Easy to spot if you crawl under there.

While the tanks do self-level, it cannot happen fast enough to let you fuel from just one side. If you do fill only one side, after a bit of driving they will equalize, unless bugs have blocked your vent lines!

Here's the explanation: https://rvunderground.com/jayco-sene...oes-this-work/
__________________
Rob R.
Akron, OH
2014 Seneca 37TS
Toads: 2019 Ford Edge ST or 2013 Ford Focus ST
Robbbyr is offline   Reply With Quote
Old 09-23-2022, 12:24 PM   #6
Senior Member
 
TWP723's Avatar
 
Join Date: Mar 2015
Location: Abingdon
Posts: 5,967
Quote:
Originally Posted by Robbbyr View Post
There are no in-tank fuel pumps on a Freightliner Seneca. The chassis uses an Equiflo system, common on big rigs to equalize the tanks since crossover lines were discontinued years ago. The fuel level sending unit is in the driver's side tank. Only one sending unit. The generator pickup and return lines are also in the driver's side tank. The fuel senders are known to be horribly innacurate. Some folks even had new ones installed with no improvement.

The old-style crossover line was effective, but subject to damage from road debris. One road alligator attack could dump a hundred gallons or more of diesel fuel into the environment in minutes.

Here is a Seneca owner's simple explanation of Equiflo, there also are very complicated ones if you go digging. The only problem I ever heard a Seneca having was uneven fuel levels side to side, the owner found that insects had blocked one of the fuel tank's vent tube. The vents come off the top of the tanks and then come down the sides of the tanks towards the center of the rig. Easy to spot if you crawl under there.

While the tanks do self-level, it cannot happen fast enough to let you fuel from just one side. If you do fill only one side, after a bit of driving they will equalize, unless bugs have blocked your vent lines!

Here's the explanation: https://rvunderground.com/jayco-sene...oes-this-work/
Answers my question if its still factory. Good to know. TY Robbbyr!
__________________
2013 Jayco Eagle 328 RLTS
2021 Keystone Montana 3121RL
2013 F350 6.7L 4x4 CCLB
W/Air Lift air bags (front & rear)
Equal-I-Zerô WDH & B&W Companion
TWP723 is offline   Reply With Quote
Old 09-25-2022, 09:56 PM   #7
Junior Member
 
Join Date: Apr 2019
Location: Golden
Posts: 8
Thanks, Rob!

Quote:
Originally Posted by Robbbyr View Post
There are no in-tank fuel pumps on a Freightliner Seneca. The chassis uses an Equiflo system, common on big rigs to equalize the tanks since crossover lines were discontinued years ago. The fuel level sending unit is in the driver's side tank. Only one sending unit. The generator pickup and return lines are also in the driver's side tank. The fuel senders are known to be horribly innacurate. Some folks even had new ones installed with no improvement.

The old-style crossover line was effective, but subject to damage from road debris. One road alligator attack could dump a hundred gallons or more of diesel fuel into the environment in minutes.

Here is a Seneca owner's simple explanation of Equiflo, there also are very complicated ones if you go digging. The only problem I ever heard a Seneca having was uneven fuel levels side to side, the owner found that insects had blocked one of the fuel tank's vent tube. The vents come off the top of the tanks and then come down the sides of the tanks towards the center of the rig. Easy to spot if you crawl under there.

While the tanks do self-level, it cannot happen fast enough to let you fuel from just one side. If you do fill only one side, after a bit of driving they will equalize, unless bugs have blocked your vent lines!

Here's the explanation: https://rvunderground.com/jayco-sene...oes-this-work/
I get it, now, Thank you. It's still going to require that we constantly guess and try to estimate how much fuel is in our tanks.
EGChester is offline   Reply With Quote
Old 09-26-2022, 06:20 AM   #8
Senior Member
 
Robbbyr's Avatar
 
Join Date: Dec 2014
Location: Akron
Posts: 3,029
Quote:
Originally Posted by EGChester View Post
I get it, now, Thank you. It's still going to require that we constantly guess and try to estimate how much fuel is in our tanks.
I have a ScanGauge in my Seneca, when I fill up I can reset it and it will keep track of fuel used by the engine. However it cannot include any fuel used by the generator while driving, but that usage is minimal. Perhaps a gallon per hour.
Attached Thumbnails
20170301_141046.jpg  
__________________
Rob R.
Akron, OH
2014 Seneca 37TS
Toads: 2019 Ford Edge ST or 2013 Ford Focus ST
Robbbyr is offline   Reply With Quote
Old 10-05-2022, 03:10 PM   #9
Junior Member
 
Join Date: Apr 2019
Location: Golden
Posts: 8
Quote:
Originally Posted by Robbbyr View Post
I have a ScanGauge in my Seneca, when I fill up I can reset it and it will keep track of fuel used by the engine. However it cannot include any fuel used by the generator while driving, but that usage is minimal. Perhaps a gallon per hour.
That's very helpful, Rob. I just ordered the ScanGauge D on Amazon. I know it keeps track of fuel usage, but it's not really going to tell me how much fuel I have remaining, is it? Seems like I need to set it when I fill up both tanks and then let it do it's thing. I'm also guessing that each of those tanks holds about 37 gallons of fuel, right?
EGChester is offline   Reply With Quote
Old 10-05-2022, 04:43 PM   #10
Senior Member
 
Robbbyr's Avatar
 
Join Date: Dec 2014
Location: Akron
Posts: 3,029
Quote:
Originally Posted by EGChester View Post
That's very helpful, Rob. I just ordered the ScanGauge D on Amazon. I know it keeps track of fuel usage, but it's not really going to tell me how much fuel I have remaining, is it? Seems like I need to set it when I fill up both tanks and then let it do it's thing. I'm also guessing that each of those tanks holds about 37 gallons of fuel, right?
Once you install your ScanGauge you have to use the instructions and do an initial setup to tell it your fuel capacity and your units of measure. Our total capacity is 74 gallons but I set mine on 70 gallons to give me a slight cushion. Not that I would ever run it down to even close to that amount!

Once set up there is a section in the manual where it explains "Trips". Once you fill up (manual discusses this) and you initiate a "Trip" the ScanGauge will keep track of fuel used, distance traveled, and average economy. It can indeed display gallons burned, gallons remaining, distance traveled, and distance to empty. The calculation for distance to empty updates as your "Trip" progresses, if you hit mountains and start burning more fuel the distance remaining will decrease. Likewise if you hit the flatlands and economy increases the distance to empty will be calculated upwards. As stated earlier any generator use will NOT be reflected, but generally that is minimal. It sounds complicated, but after a few trips and fuelings it becomes easier. What is important is that you remember to tell the system when you have fueled, I forgot that a few times!

As far as the tank capacities the passenger tank is rated to hold 40 gallons, the driver side is 34. The driver side tank is smaller due to the DEF tank being located beside it. But the Equiflo system will keep the two tanks balanced as you drive. Not balanced in gallons, but in fuel height (depth). In operation it will draw slightly more fuel from the passenger tank since it is "larger". But the fuel height (depth) will be close to the same side to side if things are working correctly.
Attached Thumbnails
ScanGauge Manual-28.jpg  
__________________
Rob R.
Akron, OH
2014 Seneca 37TS
Toads: 2019 Ford Edge ST or 2013 Ford Focus ST
Robbbyr is offline   Reply With Quote
Old 10-05-2022, 09:26 PM   #11
Senior Member
 
SloPoke's Avatar
 
Join Date: Apr 2016
Location: Kingman AZ and where our Seneca is today.
Posts: 2,917
Today... we had a little more time on our hands on our travels... and after reading these threads about the M2 Dual tank systems... we had an opportunity to do a little testing/measurement/documentation on how fast the crossover system "equiflow" works on our 2015 Seneca.

Along our travels north today, we found our fuel gauge at a little under 2/3, with a long stretch of 2-lane ahead of us with some good climbs to occupy the rest of our travel day... Gas buddy showed a Maverick within the next hour with Diesel 52-cents below every other dealer, but they did not have truck pumps... it meant that we would only fill on one side. We went for it... and did our transfer test.

Maverick Stations are consistently 14-16 foot high canopy's with Diesel on the outside islands, but we pulled up on this one with a posted height of 15'6" and as we do, pulled the passenger side up to the pump. We pulled in with the tank gauge showing just over 1/2... Our Generator was running, powering both AC units running WFO and we kept the Cummins running like always when fueling. The low flow nozzle flowed at full speed until the passenger tank was full (we have the Extendaflow adapters - Gordon is a genius!) and I checked the fuel gauge right at that moment. (just over 3/4)

Our Freightliner gauge -as RobbbbbbbbbbyR has accurately stated, is consistently off... We have taken a dip-stick and have been documenting the gauge level -vs- the tank level of the fuel in the tank. We really had about 11/16 tank on the drivers side and it was rising.

So once the passenger tank was tripping on full, I started to measure how long it would take to allow another gallon of fuel into the passenger tank after it was transferred to the drivers side tank... I would wait two minutes and almost get another gallon in it.. Of course nobody was waiting behind us, and I was cleaning a half-million bugs off the windshield in the down-time... but it seemed to be time well invested to do that testing.

Let me make note... There isn't a truck pump in a couple of hundred miles along this route... we travel it a couple of times a year and are frequently finding that we need to find fuel in these one-pump-towns in places we travel. How we can optimize our fueling time / tank 2 tank transfer / avoid moving to the other side... is our goal.

Your ideas are welcome,
__________________
Steve & Stacy with Jasper (shepherd)
2015 Seneca 36FK

Custom 27' flatbed trailer hauling our:
07 Toyota FJC & Yamaha Kodiak 400 ATV

SloPoke is offline   Reply With Quote
Old 10-06-2022, 07:10 AM   #12
Senior Member
 
Robbbyr's Avatar
 
Join Date: Dec 2014
Location: Akron
Posts: 3,029
Quote:
Originally Posted by SloPoke View Post
Let me make note... There isn't a truck pump in a couple of hundred miles along this route... we travel it a couple of times a year and are frequently finding that we need to find fuel in these one-pump-towns in places we travel. How we can optimize our fueling time / tank 2 tank transfer / avoid moving to the other side... is our goal.

Your ideas are welcome,
In the "old" days dual tank diesel trucks had a crossover line connecting the bottom of the two tanks. Ones I had seen were 1" to 1-1/2" rubber hoses. They would allow filling both from one side. The problem was is that they were vulnerable to damage from road debris causing significant fuel spills and disabling the truck. That's why the manufacturers discontinued them and went to the Equiflo system or something comparable. I'm guessing there also may have been some regulatory pressure (EPA/DOT?) involved in the decision by the truck manufacturers.

I suppose the tanks could be modified to add fittings to the bottoms and a crossover added, but then you become vulnerable to the same road hazards. That would be a passive equalization system. And don't forget a fuel spill cleanup is the responsibility of the owner of the rig that created the hazard.

I also suppose an active system could be designed involving a transfer pump and associated valves and lines. Would also likely involve new tank fittings, since I think adding it into the existing Equiflo lines and system might upset the proper drawing and returning of fuel to/from the tanks. You certainly would not want to create a situation where the engine drew fuel from one tank and returned it exclusively to the other causing it to overfill and start dumping out the vent line!
__________________
Rob R.
Akron, OH
2014 Seneca 37TS
Toads: 2019 Ford Edge ST or 2013 Ford Focus ST
Robbbyr is offline   Reply With Quote
Old 10-08-2022, 01:56 PM   #13
Junior Member
 
Join Date: Feb 2020
Location: San Tan Valley
Posts: 10
I also have a 2018 Seneca 37 HJ and have experienced the same issues with the fuel tanks. I recently had the fuel tank sensor replaced under my extended warranty with little improvement. I tracked my mileage and gallons per fill-up. As it was explained to me by the Freightliner tech, fuel is drawn to the engine via fuel pump from both tanks into a single feed line at a rate of a couple of gallons a minute and the un used fuel is returned to both tanks via a single return line that tees into both tanks. So the equalization of fuel levels in the tanks occurs from the fuel returned to both tanks over time. Hence the equalization that Slowpoke saw at the station since the engine was idling while they were there. I will invest in the Scangauge for the future. Even with my fuel gauge reading empty with the warning light on, I still have between 25-30 gallons left. It is frustrating, but the benefits of this rig outweighs the inconvenience.
SanTanSeneca is offline   Reply With Quote
Old 10-09-2022, 07:45 AM   #14
Junior Member
 
Join Date: Jul 2020
Location: Mansfield
Posts: 6
I finally purchased and installed a Bully Dog performance device which not only adds power but provides a great deal of data. One being gallons used So now I pay no particular attention to the gauge but rely on the bully dog monitor for gallons used.
johnboye is offline   Reply With Quote
Old 10-12-2022, 08:06 AM   #15
Junior Member
 
Jiggles's Avatar
 
Join Date: Jan 2017
Location: Southport
Posts: 28
Even though I have a scangauge I track my mileage. When I reach 400 miles start looking for fuel. As they had said the tanks may still have gallons o fuel but for comfort 400 miles works for me
Jiggles is offline   Reply With Quote
Old 10-12-2022, 06:09 PM   #16
Senior Member
 
DonkeyFluffer's Avatar
 
Join Date: Sep 2018
Location: Knoxville
Posts: 252
Yep. I use 400 miles. I have a working scanguage and bluefire and fuel gauge, but choose 400 miles on my S2RV chassis to fill up. Usually earlier, but 400 is my drop dead.

I try to keep it simple
DonkeyFluffer is offline   Reply With Quote
Reply

Tags
dual fuel tanks, fuel gauge, two fuel tanks

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


» Featured Campgrounds

Reviews provided by

Powered by vBadvanced CMPS v3.2.3
Disclaimer:

This website is not affiliated with or endorsed by Jayco, Inc. or any of its affiliates. This is an independent, unofficial site.


All times are GMT -6. The time now is 03:41 PM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2022, vBulletin Solutions, Inc.
Copyright 2002-2016 Social Knowledge, LLC All Rights Reserved.