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Old 09-25-2017, 12:07 PM   #1
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Seneca - Uneven Fuel Fill-ups

So I know the total fuel capacity is 74 gallons between the 34 gal left (driver side) tank and 40 gal right tank (I believe that's correct) on the M2's. I understand also that both tanks are passively or actively interconnected to presumably maintain even fuel levels. I have noticed that my right tank takes almost twice as much fuel as the left tank when refueling. Is there preferential flow from the right to the left tank, or something else going on?
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Old 09-25-2017, 02:36 PM   #2
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They wont consume at the same rates, they will equalize to the same level as in height in the tanks. They will try to keep the same level as it drains, and since their is more gas in the right tank, it will consume more gas on that one than on the left one. Should only be by a few gallons or so...not by half though. However note that it only equalizes when the engine is running. To expand on this, the generator only pulls from the right tank (at least mine does). If you boon dock for a while, your right tank will be much lower than the left. If you leave your boon dock and go right to a gas station, you may not have left enough time for the system to re-equalize and now you are having to add much more to the right than to the left tank.
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Old 09-25-2017, 04:22 PM   #3
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I found a drawing online that shows the fuel tanks. These are actually bigger tanks but you can see the configuration. Basically there are two lines in each tank. One is the pickup line and the other is the return from the engine. These are nylon lines that run to tees over the transmission. They are then tied into the corresponding line from the other tank. The pick up appears to be 5/8 and the return 1/2 in. Because the hose is at the same level siphoning will occur and the tanks level given enough time. The return line simply returns the fuel and is split at the tee.

Check your fuel tank vents as if one is blocked this will either cause a lack of siphoning and or increased pressure on that side and you will get lower return and actually that tank could get even lower as the pressure will increase usage from that side. On my unit the generator pulls off the drivers side.


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Old 09-25-2017, 04:24 PM   #4
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You can google m216_470186 to look at the drawing. Based on crawling under the unit this is very close to what I saw.


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Old 09-28-2017, 06:40 AM   #5
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Well, as I stated on another post, I learn new stuff every day. I do know the tanks equalize through a small tube on the top, not the bottoms of the tanks. I thought engine was supplied from the driver's side, but makes sense to be supplied from the passenger side, since it is bigger. Did not know about the generator running off the driver's side.
New Info and my goal of learning something new every day continues.

One thing that always concerns me is the generator stopping if fuel drops below a 1/4 of a tank. if that happens does it just stop? Or does it require a bleeding to restart because it ran out of fuel? Have never experienced this and really don't want to. I've bled many diesel engines and really not one of my favorite things.
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Old 09-28-2017, 11:03 PM   #6
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I am still quite unsure where our Generator pickup is - when they say that the fuel for the gen will shut off at 1/4 tank. I am not sure now... Here are some rudimentary observations.

We dry camped for 11 days at the shore of Flaming Gorge Res. Us and another couple in their 5er. We brought extra water with us on the trailer and had 100 gallons of extra diesel in the bed of our friends TV. We had the entire cove to ourselves, not another camp within a quarter mile from us. Our Gen was running from "making coffee time" to Campfire time - yes for 11 full days in a row. Daytime high was 103 and the low was in the 60's.

When we broke camp - the Seneca was still level and the fuel gauge said just above 1/4 - before we headed out for our first stop for fuel about 15 miles away. The first panic was when we were on our way for fuel... and the fuel gauge went to empty and the warning light came on... then it went off and showed a quarter tank... and back to Empty with the light on again... back and forth - with every hill we climbed and descended.

Did the Generator ever shut down when the fuel gauge showed empty - no. When we fueled up... we took about 63 gallons.

Thoughts: If one of the tanks was that low... would it have drawn air instead of fuel when going up/down steep hills??? Is the Generator pickup really separate from the chassis pickup??? Does the Fuel filter act as a reserve reservoir?

We expected the gen to shut down on out of fuel... but it didn't. Yes we had another 100 gallons of fuel on the other tow vehicle, but wanted to see how the gen fuel systems worked in real world - and were surprised. We learned that the gen really uses less than a half-gallon of diesel / hr running two AC units and extra stuff...
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Old 09-29-2017, 02:24 AM   #7
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Generator pick up and return lines on 2018 m2.

The two systems are separate feeds. The truck is from the sides of the tank while the gen is on top Using 62+ gallons is cutting it very close. Someone posted earlier this year that they drained their tank and refilled and only got in 63-64 gallons. Your experience does make one scratch their head. If it was that low you would have expected to lose prime on either the truck or gen or both if climbing hills.

I had the generator shut off on low fuel during my test drive but since I did not own the unit I don't know how much the dealer put in for fuel. Gauge was bouncing on empty.

Just when you think you have it figured out.....


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Old 09-29-2017, 06:14 AM   #8
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Holy cow Paul. Have you disassembled your entire Seneca? Lol. I love the info and photos that you are providing.
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Old 09-29-2017, 08:00 AM   #9
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Slowpoke, RVermont and everyone else contributing to this thread, THANK YOU! This is by far the most comforting answers I could get. Actual experience is by far the best example of what could be expected. I have experienced the gauge bouncing up and down and as we lean at a site or going up and down hills. I'm amazed that the generator keeps running. I can say, that having worked with small diesels that did not have return fuel lines and had to be bled like crazy and then diesels that did have return fuel lines and were under pressure in the line and, most of the time, self primed. Glad it looks like the generators are self priming and I guess, we need to consider the amount of fuel in the filter, fuel line (which is quite long, and the very bottom of the tanks, as far as not sucking an air bubble and then removing that air bubble at the injector pump.
As I said, quite comforting. Thank you so much for sharing your experience.
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Old 09-29-2017, 09:31 AM   #10
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Not quite the whole unit yet. I do tech service as part of my job and I have to see things to understand how they work. My biggest fear with one of these units is being stuck somewhere and unable to move due to a failure, so the more I know before that occurs allows me to enjoy the ride.

When starting the generator when you push the button it starts the priming pump. That is why sometimes it takes 20-30 seconds to turnover and others it starts in a few seconds. The starter will not turn over until it senses fluid pressure.

Still not sure why slowpoke did not run out of fuel as it sounds like he was pretty empty. I get nervous at a quarter tank as it goes from quarter to zero quickly.




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