2018 M2 Chassis fuel tank capacity

[mbpharmd1]

I was just wondering if anyone ever figured out what the useable fuel tank capacity is on the 2018 Seneca with an M2 Chassis and the saddle tanks. I know it says they are a combined 74 gallon volume but I’m sure that the actual useable capacity is a quite a bit less. Thank god I have my scan gauge hooked up because I would not have any idea what I’ve used without it. There have been times where the fuel gauge has been pegged on E for over an hour and the scan gauge will say I’ve only used 40 gallons. I never really push it much further than that but would like to get an idea of what I can really use before I have to start worrying.

[Mark S]

I called Freightliner to ask the same question and they could not answer. Based on nothing but a guess, I am using 60 gallons as my fill up number in scangauge. I figure for about 20% non usable fuel in the 74 gallon tank(s). I also have Extendfills which adds about 5 gallons of capacity so I figure I’m safe using the 60 gallon number. It sure would be nice to know for sure though.

[RVermont]

I think Mark is pretty close to what is useable. I watch the scan gage and milage and when I am around 400 miles and 45 gallons I find some fuel. Most I ever drove is 460 miles and the light was on for quite awhile. But I knew the area and wanted to get to specific station. If in unknown areas I fill around 300 miles. Also if running the generator I stop more frequently.

[Bruceter]

Not sure whether this helps as we just got the Seneca and have not yet purchased a Scan Gauge but do have Extenda Fill extension.
On the way home from dealer fuel gauge showing just a hair over 1/2, I filled to the bottom of the original filler necks and took a total for both tanks of 93liters which translates to 24.6us gallons.
After a short trip this weekend fuel gauge showing 1/3 left in tanks, filled both tanks to same height on filler necks with a total of 130liters translates to 34.4us gallons. Distance traveled 323.5 miles

I also forgot to mention that the fuel usage included 2.5hrs of generator usage

Bruce

[mbpharmd1]

Thanks for all the replies. I typically never go past 40 gallons of usage but wanted to get a better idea. Next thing I’m adding are the extenda fills. Bruceter, the scan gauge is invaluable. I only made one trip without one and wouldn’t limaginen traveling without it now. The fuels gauge on th M2 Chassis is terribly inaccurate and the real time data and scan codes are very useful.

[SloPoke]

I'm going to invest in a couple of Home Depot "yardsticks" and a 4 foot piece of PVC pipe with a couple of threaded caps that the Yardstick can fit into. The PVC tube will hold my new, highly accurate precision calibrated fuel measurement device that will be stuffed down the opening of my "ExtendaFill" extensions and measure exactly how much fuel is really in the tanks - and just maybe... well maybe not... compare that to the always inaccurate fuel gauge.

Don't try to sell me on the Scan Gauge... we have been known to spend 10-12 days in the back-country with our Diesel Generator alone keeping our systems and technology up and charged / running on our batteries ... The Scan gauge won't help me know how much fuel we have any better than the gauge on the dash.

[Mark S]

Originally Posted by SloPoke

I'm going to invest in a couple of Home Depot "yardsticks" and a 4 foot piece of PVC pipe with a couple of threaded caps that the Yardstick can fit into. The PVC tube will hold my new, highly accurate precision calibrated fuel measurement device that will be stuffed down the opening of my "ExtendaFill" extensions and measure exactly how much fuel is really in the tanks - and just maybe... well maybe not... compare that to the always inaccurate fuel gauge.

Don't try to sell me on the Scan Gauge... we have been known to spend 10-12 days in the back-country with our Diesel Generator alone keeping our systems and technology up and charged / running on our batteries ... The Scan gauge won't help me know how much fuel we have any better than the gauge on the dash.

“HAPCFMD” Good idea but I think we need to work on the acronym a bit. It needs to flow better if we are to reach the masses with our marketing campaign. Great job on the R & D. Lol

I still think it would be really helpful to know how many gallons of fuel remain in the tanks when the fuel pick up tubes no longer pick up fuel.

[SloPoke]

Originally Posted by Mark S

I still think it would be really helpful to know how many gallons of fuel remain in the tanks when the fuel pick up tubes no longer pick up fuel.

That is still an unanswered question... We spent eight days on the shoreline of Flaming Gorge and used a LOT of diesel running our genny for two rigs with AC's running. Our camping partners had an extra 100gal of "off road fuel" on their tow vehicle in case we needed some on our way out.

As we left to head back home, we fired up and the Dash gauge showed just under 1/4 tank and we had about 35 miles to get to a fuel stop - so we did not take on any fuel in camp and headed out. On our way out, we had the genny running the entire way to get fuel and it never stopped. Our FL gauge is very influenced when going uphill or down-hill. The gauge would fluctuate from almost E (with the warning light) to over 1/8 of a tank just by going up/down 3-4% grades. As I remember, we put about 60 gallons in at the fillup and was suprised that the genny did not run out of fuel (as I am led to believe that it should).

Has anyone actually run their fuel down so low that the genny has cut out?

[Mark S]

So it sounds like my 60 gallons is a good magic number.

[matthewphilippe]

We have a 16 HJ and when i took it in for an oil change at Freightliner asked for the tank sizes. They looked up the VIN number and told me the gauge level is in the driver side tank which is 30 gallons and the passenger tank is 45. I typically drive 300 -350 miles before looking for diesel, and have had to push it once to 425 miles. Only took 68 gallons.

[Crossingover]

Bit off topic, but does the high pressure fuel pump draw from a single common point between the fuel tanks, or does it draw from both tanks separately? And is there a transfer pump between the tanks? The reason I ask is last week I was fueling up and for the first time noticed my previously 'full' driver's side tank had dropped in level while I was filling the passenger side tank. The engine was off the whole time. So obviously there was some passive flow of fuel out of the driver's tank to the passenger tank.

[Mark S]

Originally Posted by matthewphilippe

l, and have had to push it once to 425 miles. Only took 68 gallons.

425 miles / 68 gallons = 6.52 mpg. Holy cow! Is that your normal MPG?

It’s good to know that you can get 68 gallons out of the tanks without running out. I’m surprised.

[Robbbyr]

Originally Posted by Crossingover

Bit off topic, but does the high pressure fuel pump draw from a single common point between the fuel tanks, or does it draw from both tanks separately? And is there a transfer pump between the tanks? The reason I ask is last week I was fueling up and for the first time noticed my previously 'full' driver's side tank had dropped in level while I was filling the passenger side tank. The engine was off the whole time. So obviously there was some passive flow of fuel out of the driver's tank to the passenger tank.

Here is a website from a fellow Seneca owner that has a quick primer on our M2 fuel systems, plus I include documents on the fuel splitter device itself.

Jayco Seneca Freightliner M2 Two Separate Fuel Tanks and Equiflo, How the hell does this work? | RV Underground

[Oma/opa]

[QUOTE=Mark S;759901]425 miles / 68 gallons = 6.52 mpg. Holy cow! Is that your normal MPG?

My thoughts exactly.
I have driven our 17 37TS about 10,000 miles since we purchased it used in July last year and have averaged 9.7 mpg driving in all terrain from flat south Florida to the mountains of Colorado and Utah. The only thing that I see affecting the MPG is wind. Not much variance between flat and mountains. Typical speed is 62mph and 1700rpm.

[matthewphilippe]

My average mileage in our 16 HJ is 9.7 with the transmission reprogramed to performance mode and towing our 03 Subaru dingy. Worst mileage was 6.8 towing my Silverado 4x4 in the mountain passes. Best mile was 11.0 running flat on the desert with our dingy.

[Mark S]

I am towing my Jeep Wrangler Sport (4,600 lbs) most of the time and average MPG is around 9.5 and about 10ish without Jeep. If I was averaging 6.5 mpg I would be checking that everything is working as it should.

But I am happy to know we can use 68 gallons without running out of fuel. I usually get very concerned after about 50 gallon used and not knowing where next truck stop is.

On a side note, my Scan Gauge “fuel used” is almost always within 1 gallon of the actual fuel I add to tanks.

[matthewphilippe]

How do you like the diesel scan gauge?
I had a gas version on our old Southwind with the 8.2 liter GM engine.

[Mark S]

Originally Posted by matthewphilippe

How do you like the diesel scan gauge?
I had a gas version on our old Southwind with the 8.2 liter GM engine.

It was the first thing I bought when I got the Seneca. I wouldn’t be without it.

[Dave and Tina Reyburn]

Hi can someone tell me about the scan gauge? Where do you buy one? Considering a Seneca purchase and it sounds like a must have.

[Dave and Tina Reyburn]

I guess Google and YouTube still work Lol. I must be living under a rock I'd never heard of them.