2018 Seneca w/ 2 Fuel Tanks - Question

[EGChester]

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???

[TWP723]

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.

[TWP723]

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.

[Onyrlef]

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.

[Robbbyr]

Originally Posted by EGChester

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/

[TWP723]

Originally Posted by Robbbyr

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!

[EGChester]

Originally Posted by Robbbyr

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.

[Robbbyr]

Originally Posted by EGChester

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.

[EGChester]

Originally Posted by Robbbyr

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?

[Robbbyr]

Originally Posted by EGChester

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.

[SloPoke]

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,

[Robbbyr]

Originally Posted by SloPoke

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!

[SanTanSeneca]

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.

[johnboye]

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.

[Jiggles]

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

[DonkeyFluffer]

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

[EGChester]

Originally Posted by Robbbyr

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.

Hey Rob -
I am finally installling the Scanguage II (the same model shwon in your photo) to my 2018 Seneca. The Seneca has a round 9 pin port under the dash on the left and the Scanguage uses a straight Obdii port. I bought a 6" adapter from one to the other and I can turn my Scanguage on, but I'm not getting any readings. Did you need the same adapter?

[Robbbyr]

Originally Posted by EGChester

Hey Rob -
I am finally installling the Scanguage II (the same model shwon in your photo) to my 2018 Seneca. The Seneca has a round 9 pin port under the dash on the left and the Scanguage uses a straight Obdii port. I bought a 6" adapter from one to the other and I can turn my Scanguage on, but I'm not getting any readings. Did you need the same adapter?

My ScanGauge model is the ScanGauge D (for diesel) and its cord plugged right into my rig's round diagnostic port. No adapter needed.

The ScanGauge II is used on light-duty vehicles that have the traditional OBD port, not the connection Freightliner uses.

[EGChester]

Yo Rob - I now have the right ScanGuage (a D) installed. Thank you. But I don't get how to monitor fuel level. With two deisel tanks, both now on full, how do I know how much fuel is left in each toank or together? If you want to call to walk me through this, I'm in Denver at 303-eight ten - thirty three hundred. Thank you!!

[Robbbyr]

Originally Posted by EGChester

Yo Rob - I now have the right ScanGuage (a D) installed. Thank you. But I don't get how to monitor fuel level. With two diesel tanks, both now on full, how do I know how much fuel is left in each tank or together? If you want to call to walk me through this, I'm in Denver at 303-eight ten - thirty three hundred. Thank you!!

Sorry, I did not see this until now. Working on replacing my garage heater, old one died!

To start, the ScanGauge calculates fuel usage from both tanks, there is no way to separate the two. When full, we have 74 gallons (total) between the two tanks. The Equiflo fuel system works to keep the tanks at the same LEVEL, but by virtue of the fact our passenger side tank is larger at the same LEVEL it still contains a bit more fuel. But we shouldn't generally worry about that, we are more concerned with the total fuel consumed as we go.

Glad you got the new unit in and working. The best advice I can give is to get the instructions, read carefully several times, and do the "Basic Setup Parameters". Pretty straightforward. However I did deviate on fuel tank size. Instead of entering our full 74 gallon figure I have my capacity set at only 70 gallons. I would never run it near that low, but it makes me feel better.

Now to see fuel burned you have to use the "Trips" functionality of the unit. You tell the ScanGauge you are full of fuel, and it will track fuel usage as you drive. I will attach a page from my manual, but consult yours since it may have updated information from mine. You have to try to fill the unit consistently so certain information is consistent between trips. In other words if you tell ScanGauge your tanks are full, but really they are not, your "distance to empty" and "time to empty" will not be correct. It will still show fuel used, but if tanks were not full then that information might not be very useful to see what you actually have left.

It takes numerous times using the "Trip" functions to get proficient, and you don't want to try manipulating it too much while you drive. It can be very distracting! However if your ScanGauge is mounted somewhere your copilot can operate it that might be helpful. I have mine above my head, so I set up mine before departing. But I can easily jump to a trip (safely) and glance up at the numbers now that I am more familiar with it.

One additional point about fuel used. It only calculates what the chassis engine burns. It DOES NOT take into account any generator usage. You have to manually estimate what you may have used and deduct that amount from your "remaining fuel" in your head. A properly running 8,000 watt Onan will burn about 0.5 gallon/hour at 50% load, a touch over 1.0 gallon/hour full load. Not a big deal if you are cruising down the highway running it between fuel stops, but if you are counting on ScanGauge to be accurate on your remaining fuel after boondocking for a week running the generator a lot it will not be. I hope that generator caveat make sense.

It took me a bit of practice to get comfortable, I'm sure you will too after you gain some experience.