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Old 05-31-2020, 06:07 AM   #1
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fuel gauge on M2 - frustrated

I am starting to get very frustrated with the error in the Freightliner's fuel gauge. I know this has been covered a few times but I just want to throw it back out there as in my case it seems very excessive.

We filled up the rig, passenger side first then drivers, just as Freightliner and the internet says is the right protocol. Drove to Sebring and back for a quick post lock down track day, 340 mile. We ran the generator for a night as we had to boon-dock outside the track for the night, 15hrs. Then yesterday we went to a quiet spot near the Everglades, 20 miles. Gauge read empty!

360 miles and 15 hours on genny and the tanks are empty! I knew there was still fuel in the tank but not knowing how much I decided to get a splash before getting to our destination so we could use the genny without worry. The drivers side tank took all of 25 gals, its a 40 gal tank! (I only filled the one side this time as the stations in Miami are 50c a gallon pricier then by the house)

The gauge is showing empty at nearly half a tank!

Are the rest of you all getting this bad a reading and just estimating fuel by mileage?

Thanks

Miguel
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Old 05-31-2020, 07:02 AM   #2
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Originally Posted by racer32 View Post
I am starting to get very frustrated with the error in the Freightliner's fuel gauge. I know this has been covered a few times but I just want to throw it back out there as in my case it seems very excessive.

We filled up the rig, passenger side first then drivers, just as Freightliner and the internet says is the right protocol. Drove to Sebring and back for a quick post lock down track day, 340 mile. We ran the generator for a night as we had to boon-dock outside the track for the night, 15hrs. Then yesterday we went to a quiet spot near the Everglades, 20 miles. Gauge read empty!

360 miles and 15 hours on genny and the tanks are empty! I knew there was still fuel in the tank but not knowing how much I decided to get a splash before getting to our destination so we could use the genny without worry. The drivers side tank took all of 25 gals, its a 40 gal tank! (I only filled the one side this time as the stations in Miami are 50c a gallon pricier then by the house)



The gauge is showing empty at nearly half a tank!

Are the rest of you all getting this bad a reading and just estimating fuel by mileage?

Thanks



Miguel

Yes, same problem here. Dash gauge has never been accurate. When mine reads a quarter tank of fuel, I fuel up with only 40 gallons. With 100 gallon capacity, that means I have 60 gallons remaining when the gauge reads approximately 25 gallons remaining. I installed a Scan Gauge to more accurately read "Fuel to Empty" on the gauge and ignore the dash gauge. Still it is disconcerting to know dash gauge is almost worthless. Am considering having a Freighliner dealer fix it. But then I will have to pay for something that should have been right when we purchased it.

So some of us feel you pain but the Scan Gauge can help. Scan Gauge D for diesel.

https://www.amazon.com/ScanGauge-SGD...0926417&sr=8-2
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Old 05-31-2020, 07:04 AM   #3
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My gauge is nowhere near accurate. First, it never shows completely full and second, it shows empty when there is probably over 50 gallons between the two tanks. Kinda learned how to “gauge” it myself now based on 16,000 miles of travel. Plus, my ScanGauge tells me how many gallons I have used. (If I remember to tell it I filled up!)

Our M2 112 carries a total of 100 gallons, but I have the ScanGauge set for 90 gallons at fill up because it is not possible to fill to the brim, nor are we supposed to as I understand it.
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Old 05-31-2020, 09:03 AM   #4
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I have the same issue. I took it to the dealer and they said there is a ring installed below the sending unit so it will not read correctly. I included the invoice explaining the diagnosis. My gauge still reads incorrectly and I also rely on the scan gauge and mileage.
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Old 05-31-2020, 09:48 AM   #5
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Yep looks like that scan tool is what I'll need to add. Thanks for suggestions!

A couple of additional questions:
1. Rough estimate of consumption with generator running 1 ac?
2. The quarter tank shut off on generator, is this a function of were the pickup is in the tank or something more technical that prevents one from running generator dry?

M
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Old 05-31-2020, 09:58 AM   #6
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Mine seems to be fairly accurate. I generally refill at 1/2 tank and put in about 40-45 gallons. You would think if it is a design issue, it would be consistent across all trucks.

Gauge showing empty when there is 50 gallons left is a big error to me. I would think something is broke like you suspect.

Be interesting to collect chassis data by year on this forum to see if you can detect trends:

Mine: 2018 - good.
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Old 05-31-2020, 10:29 AM   #7
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Originally Posted by racer32 View Post
Yep looks like that scan tool is what I'll need to add. Thanks for suggestions!

A couple of additional questions:
1. Rough estimate of consumption with generator running 1 ac?
2. The quarter tank shut off on generator, is this a function of were the pickup is in the tank or something more technical that prevents one from running generator dry?

M
1. We always estimate 1 gallon per hour when running the generator, and that seems to be on the conservative side.

2. Someone will correct me if I’m wrong here, but I’m pretty sure that the fuel supply for the generator is physically connected roughly 1/4 up from the bottom of the tank, AND I’m pretty sure it’s only fed from the driver’s side tank. No way for the generator to leave you stranded.

JT
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Old 05-31-2020, 10:40 AM   #8
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Originally Posted by racer32 View Post
Yep looks like that scan tool is what I'll need to add. Thanks for suggestions!

A couple of additional questions:
1. Rough estimate of consumption with generator running 1 ac?
2. The quarter tank shut off on generator, is this a function of were the pickup is in the tank or something more technical that prevents one from running generator dry?

M
1. I have a 8kw. Ran it constantly from approx Fri 3pm - Mon 10 am (approx 65 hrs). It was in Louisiana in Jun/July. Ran two A/C’s during the day and only one at night. Used slightly under 1/2 tank (so, maybe 60 gallons). So, I figured gen consumed just under a gallon/hr which was in accordance with the manual—since I was never under a full load.

2. I do not have experience with the 1/4 tank shutoff. I’ve been told that the gen pickup tube is just a 1/4 up from bottom of tank—nothing fancy just a physical thing.
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Old 05-31-2020, 10:43 AM   #9
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Oops...Mookie and I were submitting at same time. Looks like you get two data points.
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Old 05-31-2020, 12:06 PM   #10
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great thanks for the suggestions and answers!

Clear and concise. Will roll with these estimates till I pick up a Scan Gauge.

M
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Old 05-31-2020, 04:35 PM   #11
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1. I have a 8kw. Ran it constantly from approx Fri 3pm - Mon 10 am (approx 65 hrs). It was in Louisiana in Jun/July. Ran two A/C’s during the day and only one at night. Used slightly under 1/2 tank (so, maybe 60 gallons). So, I figured gen consumed just under a gallon/hr which was in accordance with the manual—since I was never under a full load.

2. I do not have experience with the 1/4 tank shutoff. I’ve been told that the gen pickup tube is just a 1/4 up from bottom of tank—nothing fancy just a physical thing.
I'm confused, how do your run 60 gallons from one 50 gallon tank. Like Mookie, I was under the impression that the gen only runs from the drivers side tank and the two tanks are not connected? Hope I'm wrong as I have a boondocking trip coming up next month and was trying to determine how to run the generator two 2 days without adding fuel.
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Old 05-31-2020, 05:03 PM   #12
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I'm confused, how do your run 60 gallons from one 50 gallon tank. Like Mookie, I was under the impression that the gen only runs from the drivers side tank and the two tanks are not connected? Hope I'm wrong as I have a boondocking trip coming up next month and was trying to determine how to run the generator two 2 days without adding fuel.

The two tanks are connected with a tube that keeps tank levels balanced out. The gen only needs to pick up its fuel from only one of them.
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Old 05-31-2020, 05:18 PM   #13
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The two tanks are connected. Its called Equalflow. or something like that, Look under the tanks and you will see two copper like tubes from one tank to the other. I had a 2014 Seneca and now a 2020 Dx3. Both seemed to read fuel ok.
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Old 05-31-2020, 05:26 PM   #14
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It's my understanding that older trucks would have had a line joining them at the bottom. This was done away with in fear of being torn off in spilling fuel.

Later trucks split the fuel return line from the fuel rail into both tanks. In enough time the tanks balance but the engine needs to be running and it takes a while.

For a delivery truck this works fine. In our application it would probably not be a bad idea to have a transfer pump... Maybe the newer M2 chassis do something like this?

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Old 05-31-2020, 06:18 PM   #15
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This is my understanding as well (regarding balancing the tanks on the return line). The implication for long term generator use while boondocking is that eventually you’ll need to run the coach in order to balance the tanks so the generator has more fuel available in the driver’s side tank.
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Old 05-31-2020, 07:34 PM   #16
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Clear and concise. Will roll with these estimates till I pick up a Scan Gauge.



M


May want try the BlueFire product instead. I am about to switch from the Scan Gauge. Scan Gauge is somewhat hard to read and the screen is small, requiring you to cycle through to get all the available data. It appears I can customize the screen on the BlueFire to include more data at a glance.
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Old 05-31-2020, 07:37 PM   #17
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Well, now you have me wondering about it too. If I made some bad assumptions, then the new results are much better than I anticipated!

Aside: I looked briefly at both my tanks and there are two hoses running to/from each about a few inches below the 1/2 way welded seam of each tank. I assumed these hoses had something to do with the fuel balancing but they could be running to the generator—it is storming too bad to crawl underneath to look.

I reviewed my notes from the 2019 trip and I noted that I had gone approx 72hrs and had over 1/4+ tank of diesel left. Before the test, we filled up off interstate and we had to travel to our destination—so probably used about 6-8 gallons before drivewaydocking for the weekend. So, rechecking my original math 100 gallon capacity - 8 gallons to destination - 33 gallons remaining = 59 gallons used by gen. (But again this could be based on a bad assumption).

If I assume gen only from pulled from 1 tank, then at my destination I should have had 46 gallons in each balanced tank (100 - 8)/2. With approx 12 gallons reserved for the 1/4 tank pickup tube in drivers tank, then that would have left me with 46 gallons available -12 gallons reserved in driver tank= 34 gallons used by gen—approx a 1/2 gallon per hour!

At end of the weekend, Our refuel stop was about 3 miles away and at a single pump, so I just filled the driver side tank and spent $63, but I don’t know what the price of diesel was last July in Louisiana. If it were $3/gallon then that would have been 21 gallons to fill up drivers tank.

So, it is possible I misread this whole thing based on my assumptions of gen pulling from both tanks—math works for single tank too. Means my gen actually used approx 1/2 gallon per hour (which is really awesome), the trip to the refuel stop was not long enough to completely rebalance tanks but it did rebalance some (probably 1 hr went by with hooking up toad and saying goodbyes and traveling to Fuel pump making rebalancing approx 15 gallons/hr—another good data point), and that I was really on the cusp of gen stopping and didn’t know it.

Next time I boondock for the weekend, I will get a flashlight and visually inspect fuel levels in each tank and redo the experiment. This will tell me what is really happening. But, knowing I could potentially boondock twice as long is exciting revelation too!
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Old 05-31-2020, 09:20 PM   #18
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Totally uninformed comment

This is a totally uninformed comment. It could be completely out in left field. I'm just reading between the lines of the vehicle technician's report.

It seems that in adding the generator, they tap into the fuel supply by removing the gas gauge and inserting an interposer ring between the gauge flange and tank. This lifts the gauge float. They can make an attempt at compensating by bending the float arm. (Kinda like bending the float arm in a residential toilet tank to change the fill level.)

The problem is that the gauges are not linear. They swing in an arc, just like the toilet float. An inch change of fuel at the bottom is fewer degrees of arc than an inch near the top--think about the geometry.

The best you can do is to make sure the gauge is accurate at one point. I expect the vehicle designers may go for the middle--also need to make sure that the user can get to F when filling the tank as failure would lead to customer complaints.

But what you really want to know is how close you are to empty. Can I make the next city where there's discount gas, or will I have to stop at a country store? To do this you have to figure out when you're down to 3-5 gallons left and bend the arm so the gauge reads E. Then learn where 1/4, 1/2, 3/4 and full are on the gauge.

This problem is not unique to your vehicle. DW and I have a Tahoe and (had) a Yukon XL. When the gauges get down to 1/2, the tank is 3/4 empty. That last "1/2" goes real quick. After a while we learned to start looking for gas at 3/8 or 1/4.
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Old 06-01-2020, 07:51 AM   #19
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It's my understanding that older trucks would have had a line joining them at the bottom. This was done away with in fear of being torn off in spilling fuel.

Later trucks split the fuel return line from the fuel rail into both tanks. In enough time the tanks balance but the engine needs to be running and it takes a while.

For a delivery truck this works fine. In our application it would probably not be a bad idea to have a transfer pump... Maybe the newer M2 chassis do something like this?

M
Quote:
Originally Posted by mookieblaylock View Post
This is my understanding as well (regarding balancing the tanks on the return line). The implication for long term generator use while boondocking is that eventually you’ll need to run the coach in order to balance the tanks so the generator has more fuel available in the driver’s side tank.
That's is what I had been told as well. Guess I will get the roller out today and get under the coach for a visual.
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Old 06-01-2020, 08:52 AM   #20
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Dual feed dual return fuel system. I'm assuming, can't find this on the Internet, that if I have half a tank in the drivers side and the passenger side runs dry, am I screwed? I don't think diesel engines like air in the system.

Just wondering if there is some kind of check valve or something that would shut off the flow from an empty tank. Probably wishful thinking.
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