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Old 06-19-2022, 09:59 AM   #1
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Fuel gauge accuracy

2021 Dynamax Force HD 37BD

What are everybody’s opinions on the diesel gauge accuracy? No matter how much I try to top it off, it usually only reads about seven eights of a tank at most.

Then when I almost touch the red in the last quarter tank, I usually stop and fill up. Being that it never reads full, is it possible to run well into the red on the gauge? it seems like I should be safe to run another hundred miles or two while in the red.
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Old 06-19-2022, 10:23 AM   #2
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No matter what type of rig you have, gas or diesel, I would never run it that low on fuel. That is an invitation to suck water and/or sediment into your fuel system. As far as fuel gauges go I have never relied on one as a measuring device. I only use it as an indicating device. Once I hit 1/2 I'm ready to refuel.
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Old 06-19-2022, 11:08 AM   #3
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Fuel gauge accuracy

Me too. I really try hard to never let it get below about 1/3 full. I find that each quarter of a tank on the gauge of my Force HD corresponds to about 20 gallons of fuel. So when the gauge shows about half full, I figure I’ve used about 40 gallons, and it’s time to start thinking about refueling. You can never tell when you might be further away from the next convenient fuel stop than you thought.
I know that lots of guys use after market products to be more accurate, but this is what works for me, it doesn’t cost anything, and it’s one less thing to worry about.
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Old 06-19-2022, 11:14 AM   #4
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2021 Dynamax Force HD 37BD

What are everybody’s opinions on the diesel gauge accuracy? No matter how much I try to top it off, it usually only reads about seven eights of a tank at most.

Then when I almost touch the red in the last quarter tank, I usually stop and fill up. Being that it never reads full, is it possible to run well into the red on the gauge? it seems like I should be safe to run another hundred miles or two while in the red.
Identify the capacity of the fuel tank and then when filling up note how many gallons of fuel were pumped in. Subtract the two and that determines how much fuel remains in the tank.

It does sound like the fuel gauge is off, but who knows at this point.
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Old 06-19-2022, 04:27 PM   #5
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Yes the fuel guage almost never shows 100% full. If you fill the passenger tank first i have had better luck getting to the full mark. Also even though it doenst show full it does seam to take a while before the guage moves.
I never intentionally run my DX3 into the red zone!!!
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Old 06-19-2022, 09:09 PM   #6
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I do intentionally run my DX3 into the red zone, even at the bottom of the red it still has 25 gallons of fuel!

I stopped last night and I was into the red zone. Started the generator (needed AC) and went to sleep. Woke up this morning gen was still running. Went to lunch gen was still running when I got back.

We all know the generator draws from about 1/8 of the tank so it doesn’t leave you stranded. Therefore I still had a lot of fuel left. So filling before the red zone is seriously a waste of time. I did this when I first got the unit and it only took about 45 gallons. I had more than 50% still left!!!

Anyways, I run most vehicles into the red. Some I have had for 15 years. Still no issues. Now if I’m in a remote area I’m not going to do that, don’t want to run out, but why stop when you have a lot of gallons in the tank???

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Old 06-19-2022, 10:03 PM   #7
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I have run mine until the low fuel light just came on and it still only took 69 gallons to fill it, so I still had 31 gallons remaining. Filling the passenger side tank first definitely helps get a more accurate reading. I am traveling pretty heavy, pulling a 12,000 pound trailer, and I usually go 400 miles on a tank which will take about 53-60 gallons to fill. So still a lot of fuel left if I need to push it a little.
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Old 06-19-2022, 10:28 PM   #8
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Great Information concerning the M2 Fuel Gauges

Newbie here with 22 XL. Never yet ran it into the red but now I won't be shy if needed. I have had it right about to enter the red and it only took 63 gallons. I agree about topping off passenger side and then topping off the driver side. Never have I gotten the gauge to the 100% full mark but pretty close...it sucks to watch diesel run down the side when trying to get it max full

I am not sure I agree with the comments about not letting it get near empty. The fuel pickup is at the bottom of the tank (we would presume) so your going to get stuff at the bottom into the fuel system.

I will be running two additives from now on based upon advice from a former Foretravel Dealer. I will run Diesel Kleen and Biobor JF https://www.amazon.com/dp/B007ILFKS6...roduct_details

Apparently we will be getting lots of water at the bottom of our tanks. I do intend to learn how to purge said water from the fuel filter(s). The Biobor JF is supposed to greatly help keep the bottom of our tanks from becoming green with slime caused by water and other stuff.

Stuck in San Diego catching Protons for another 5 weeks.
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Old 06-20-2022, 05:33 AM   #9
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No matter what type of rig you have, gas or diesel, I would never run it that low on fuel. That is an invitation to suck water and/or sediment into your fuel system. As far as fuel gauges go I have never relied on one as a measuring device. I only use it as an indicating device. Once I hit 1/2 I'm ready to refuel.
Water sinks to the bottom of a gas tank as it is more dense, so fuel level is irrelevant.
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Old 06-20-2022, 07:46 AM   #10
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I have run mine until the low fuel light just came on and it still only took 69 gallons to fill it, so I still had 31 gallons remaining. Filling the passenger side tank first definitely helps get a more accurate reading. I am traveling pretty heavy, pulling a 12,000 pound trailer, and I usually go 400 miles on a tank which will take about 53-60 gallons to fill. So still a lot of fuel left if I need to push it a little.


The tank capacity on our M2’s is officially 100 gallons. Generally there is about 10% of that capacity that will never be used. So, usable capacity is about 90 gallons. Just look at the fuel filler neck location and the level of the fuel in the tank when “full”. The gap above the fuel to the top of the tank is that 10% or 10 gallons to allow for expansion. My belief is, given the location of the fuel filler neck, you can never get 50 total gallons in each tank. So, assuming you actually have 100 gallons of fuel on board could leave you a little short in some situations.

I have verified this with my BlueFire adapter. It is set to “compute” fuel level based on the fuel flow and mileage, not reading fuel level from the vehicle’s onboard computer, which is what is indicated on the instrument panel fuel gauge. And, as several have said, not very accurate, to say the least. I have the BlueFire set to a 90 gallon fuel capacity. Every time I tell the BlueFire I filled up, it resets to 90 gallons, the instrument panel gauge shows completely full with the indicator touching the white full line. The next time I refuel, the amount of fuel I pump is usually within .5 to 1 gallon of what the BlueFire indicates I have used. For example, I start full at 90 gallons and stop for fuel with the BlueFire indicating 45 gallons left in the tank. When I fill up it will take 45 to 46 gallons of fuel as indicated on the gas pump.

My $.02.
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Old 06-20-2022, 09:00 AM   #11
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Water sinks to the bottom of a gas tank as it is more dense, so fuel level is irrelevant.
If that were true there would be no need for fuel filters and fuel-water separators. Bypass them on a diesel rig and see how far you get.
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Old 06-20-2022, 01:45 PM   #12
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Our new XL came in right at 60 gallons needed when the low fuel light lit. With today's prices, that is plenty to hurt during a fill-up.


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Old 06-20-2022, 05:56 PM   #13
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When on the road we (DW, 2 dogs, and me) stop at a fuel station and top off. That way we don't have to really worry about fuel for the day.

It cost just as much to keep the top half full as it does running it way down.
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Old 06-20-2022, 06:01 PM   #14
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Actually, with the way fuel prices are increasing on a daily basis, it’s cheaper to fill up whenever possible. It will cost more tomorrow!
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Old 06-21-2022, 09:09 AM   #15
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My observations concur with this post.

Quote:
Originally Posted by MoJoe1003 View Post
The tank capacity on our M2’s is officially 100 gallons. Generally there is about 10% of that capacity that will never be used. So, usable capacity is about 90 gallons. Just look at the fuel filler neck location and the level of the fuel in the tank when “full”. The gap above the fuel to the top of the tank is that 10% or 10 gallons to allow for expansion. My belief is, given the location of the fuel filler neck, you can never get 50 total gallons in each tank. So, assuming you actually have 100 gallons of fuel on board could leave you a little short in some situations.

I have verified this with my BlueFire adapter. It is set to “compute” fuel level based on the fuel flow and mileage, not reading fuel level from the vehicle’s onboard computer, which is what is indicated on the instrument panel fuel gauge. And, as several have said, not very accurate, to say the least. I have the BlueFire set to a 90 gallon fuel capacity. Every time I tell the BlueFire I filled up, it resets to 90 gallons, the instrument panel gauge shows completely full with the indicator touching the white full line. The next time I refuel, the amount of fuel I pump is usually within .5 to 1 gallon of what the BlueFire indicates I have used. For example, I start full at 90 gallons and stop for fuel with the BlueFire indicating 45 gallons left in the tank. When I fill up it will take 45 to 46 gallons of fuel as indicated on the gas pump.

My $.02.
Thank you, its nice to see someone who has the same numbers I have come up with and I only have 3k miles on mine.
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Old 06-21-2022, 04:31 PM   #16
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If that were true there would be no need for fuel filters and fuel-water separators. Bypass them on a diesel rig and see how far you get.
Correct me if I'm wrong, but isn't the fuel pick up tube at the bottom of the tank? I don't believe that we have a floating fuel pick up, but I may be wrong.

If the pickup is at the bottom, then whether you have a full tank or 1/8 tank, any water contamination will always end up on the bottom, as will any non-floating debris. That is exactly the reason that we have filters and water separators (and no, I don't want to run my rig without). Water separators work on the principle of density, water sinks when added to either diesel or gas.
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Old 06-22-2022, 11:27 AM   #17
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All good information here, gives me a little more to investigate. We went from Fort Worth to Nashville this past Saturday, then right back home on Monday. I had the cruise control set at 75 probably 80% of the way.

And with never having the needle touch full and filling up when we touched the red/fuel light coming on, I estimate I used a tank and a half each way.

So if we estimate the tanks actually hold 90 gallons because of where the fillers are located, giving us 22.5 gallons per quarter tank, that is 135 gallons used one way on a 720 mile trip putting us at 5.3mpg.

But it still seems like there is more fuel than we are figuring when it hits the red. The red still shows a 1/8 tank left, which is when we filled up. And I would be able to put 57-60 gallons back in.

So do we have 30 gallons left when we hit the red?
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Old 06-22-2022, 12:16 PM   #18
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I set my speed control at 65 mph and normally average 8.3 mpg with the XL engine and towing my Jeep. At these fuel prices I’m content to slow down and enjoy the journey. Plus, stopping these 30K lb rigs from 75 vs 65 is significant. That being said, I was content slowing down and enjoying the journey when diesel was $3.15 a gallon.
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Old 06-22-2022, 05:14 PM   #19
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We are currently running around Alaska, our trip up the Alcan and touring around Alaska our speeds are usually 55-65 which is getting us just under 8 mpg and that is towing a 12,000 enclosed trailer. Slowing down makes a nice difference.
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Old 07-01-2022, 10:11 PM   #20
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There is a good reason I never worry about going to the bottom of the tank. But first let me say, I don’t do it on purpose, I just wait till the fuel light comes on to start looking for fuel, that leaves plenty of fuel in the tank.

But sometimes I’m in a situation where I’m forced to run it lower than that. Here’s why I don’t worry. At SEMA Las Vegas a few years back I was speaking with a engineer from Ford about this situation. He said “The idea that if you suck fuel from the bottom you will get dirt and water is IMPOSSIBLE”. He explained why: “First of all the fuel pickup is at the lowest part of a fuel tank, usually just a bit off the bottom. If dirt and water build up on the bottom of the tank, and that is true, then after a vehicle is 10-15 years old you would have gallons of it on the bottom of the tank. And then you would constantly be sucking a bit of that contaminated mixture at all times”. He continued to explain as a vehicle moves you stir up all contents in the tank like salad dressing. You suck up the debris and water continuously as you drive at all fuel levels, therefore being worried to use fuel from the bottom of the tank is a myth. Also, if this was true your fuel filters would last forever.

It made sense. If they build up at the bottom they would eventually fill the tank if that myth was true! Think salad dressing.

If someone can disprove this explanation from the ford engineer I would love to hear it.

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