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Old 08-18-2020, 04:46 PM   #1
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Brand: Thor Motor Coach
Model: Magnitude BH35
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Thor Magnitude F-550 Fuel Distribution

Magnitude/Omni Owners,

I have a question on how the fuel tanks really work on the F550 Chassis that the Magnitude is on. I know and have verified that the chassis will pull fuel from the front tank for about a quarter of a tank before it move to the back fuel tank and pulls from it.
I understand why Ford and Thor pull from the front tank to just above 3/4 tank, allowing plenty of fuel for the generator. My question is, at what point does the chassis move fuel draw from the back tank to the front tank and begin to draw from that tank again. I have burned the fuel down to just above a quarter tank left and don't think it has transferred back to the front tank. Does any one know how this works and do we know if there is a manual way to change between the two tanks if needed

Thanks
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Old 08-18-2020, 05:01 PM   #2
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Why do you think it didn't transfer?
The Gauge deciding transfer percentage of full has been around for years by lots of different makers.
My 2004 Chevy does it.

There's nothing new about it and I'm not sure waht the worry is.

My truck will stay at the 3/4 of a tank for a disproportionate amount of time.
I just fill up whenever my low fuel comfort level is passed.
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Old 08-18-2020, 09:57 PM   #3
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When it's pretty much bone dry. You can watch them individually on the dash display, as the combined display can be a bit off with the algorithm for both. I try to schedule my stops to just fill the back tank and keep the front at 3/4, as the front doesn't like to take fuel well and it's a pain sometimes to do them both. And no, you can't control them yourself.
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Old 08-18-2020, 10:04 PM   #4
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Thanks David, pretty much what I was thinking, just wanted to verify

Matt
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Old 08-18-2020, 10:51 PM   #5
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When both tanks are full on my SV34, the front tank draws down first to about 3/4 and then switches to the rear tank. When the rear tank gets down to 1/4, it switches back over to the front tank.
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Old 08-18-2020, 10:59 PM   #6
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Quote:
Originally Posted by Judge View Post
When both tanks are full on my SV34, the front tank draws down first to about 3/4 and then switches to the rear tank. When the rear tank gets down to 1/4, it switches back over to the front tank.
Better get that fixed when you're in Wakarusa
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Old 08-30-2020, 02:50 AM   #7
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Quote:
Originally Posted by cbach View Post
Better get that fixed when you're in Wakarusa
Why should Judge get that fixed, cbach? Is that not what it is supposed to do?

Also, we are pretty new to RVing and looking for a maintenance schedule for the chassis and also for the back "functions". Is there something like this published?

BTW, we have been so busy with the punch list for the back of the coach issues working through Camping World, many times our coach sitting for weeks, sometimes months, only to pick it back up with nothing completed from our list.

We have had no time to address first year warranty issues on the chassis (i.e., our sunglass holder was missing from the beginning and we get some error notifications when driving, etc.). Hopefully, we don't get push back from Ford on these things?

Any help with maintenance schedules is greatly appreciated!
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Old 08-30-2020, 04:54 AM   #8
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Originally Posted by Pandamonium View Post
Why should Judge get that fixed, cbach? Is that not what it is supposed to do?

If in fact it's switching back over to the front tank with 10 gallons left in the rear (1/4) tank, I don't believe it will switch back when the front goes empty. Therefor, either you're short 90 miles of potential travel distance, or the gauge is wrong and you don't know for sure what's left in that tank. After the front goes to 3/4, my back tank goes to empty with a few gallons left before switching back, which I believe is per design, so I can accurately gauge my range as such.
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Old 08-30-2020, 11:57 AM   #9
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The last time I filled up I put over 38 gallons in the rear tank... but I did not specifically look at the gauge for that tank when filling up. It only holds 40 so I'd say I used the entire tank.

In any case..... anything with the fuel delivery system, gauges, etc. would be dealt with by Ford and not Thor since it is specific to the chassis.
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Old 08-30-2020, 12:11 PM   #10
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Not sure if everyone realizes this. It is not actually switching tanks. When both full you are pulling fuel from the front tank is correct. When front tank gets to 3/4 fuel is pumped from rear tank into front tank. The front tank fuel pump is the only one feeding the engine.
Quote:
Originally Posted by Judge View Post
When both tanks are full on my SV34, the front tank draws down first to about 3/4 and then switches to the rear tank. When the rear tank gets down to 1/4, it switches back over to the front tank.
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Old 08-30-2020, 12:17 PM   #11
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Originally Posted by RickD0 View Post
Not sure if everyone realizes this. It is not actually switching tanks. When both full you are pulling fuel from the front tank is correct. When front tank gets to 3/4 fuel is pumped from rear tank into front tank. The front tank fuel pump is the only one feeding the engine.
Actually..... I think I do remember reading that it does pump fuel from one tank to another and I was using "switching" generically.

However, if you do run out of gas completely it won't just pump fuel from the rear tank to the front tank if you only put fuel int he rear tank. You have to physically put fuel in the front tank before the engine will get fuel to start.
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Old 08-30-2020, 10:46 PM   #12
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All fine and good either way, but riddle me this. I ran the back until it "switched" back to the 3/4 full front, then ran the front down to about 1/4, and then filled the back full without adding to front. Front stayed at 1/4 until back ran empty again. To me that says something is actually switching and not transferring fuel forward
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Old 08-31-2020, 05:06 PM   #13
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Quote:
Originally Posted by cbach View Post
All fine and good either way, but riddle me this. I ran the back until it "switched" back to the 3/4 full front, then ran the front down to about 1/4, and then filled the back full without adding to front. Front stayed at 1/4 until back ran empty again. To me that says something is actually switching and not transferring fuel forward
HaHa got me on that one. It does make sense to me that this way the fuel in the front tank is always fresh. I have not idea why yours did that unless you confused the pumps and it only pumps a certain amount forward at a time?? Totally guessing here!
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Old 08-31-2020, 06:52 PM   #14
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I stopped being lazy and pulled this out of the 2019 Ford F-550 Manual:


Dual Fuel Tanks (If Equipped)

Your vehicle may have a dual fuel tank
delivery system which operates
independently and automatically. The fuel
pump in the front fuel tank delivers fuel to
the engine. When the fuel level in the front
fuel tank drops below three quarter full,
fuel automatically transfers from the rear
fuel tank to the front fuel tank. Whenever
there is fuel in the rear fuel tank, the front
fuel tank level remains between half and
three quarter full.

Note: If your vehicle runs out of fuel, you
must add fuel to the front fuel tank to
restart the engine.


So we can say for certainty that the front take is used first (assuming it is full)and until it reaches 3/4 full and then fuel transfers from the rear tank to the front tank. As longs as there is fuel in the rear tank, the front tank will remain at ~3/4 full.
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Old 08-31-2020, 06:56 PM   #15
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And while I was at it, I thought I would post this as well. It mirrors what I had posted in another thread when someone thought they had a problem because the pump would kick off and they had to lower the flow rate out of the nozzle at a truck stop:

Diesel fuel dispensing nozzle fill rate:

Your vehicle has a fuel fill pipe that is able
to accept fuel up to 20 gal (76 L) per
minute from an 1.2 in (30 mm)
fuel-dispensing nozzle. Pumping fuel at
greater flow rates may result in premature
nozzle shut-off or spit back.
Truck stops have pumps and nozzles
designed for larger, heavy-duty trucks.
When refueling at truck stops: if the nozzle
shuts off repeatedly when refueling, wait
5–10 seconds; then use a slower rate of
flow, do not depress the nozzle trigger as
far.



For a standard F-550 truck, the plumbing may be different than the Omni Magnitude. I can tell you it won't take 20 gallons per minute. There is a 90 degree bend in the fuel filling pipe in the Omni / Magnitude so it will back up and start foaming at high rates and kick off the pump.
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Old 08-31-2020, 07:03 PM   #16
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Yes I have a bitch of a time when filling my front tank and have to hold the nozzle while filling. The rear tank fills easily unattended. (Except with HIFLOW dispensers found at interstate truck stops) Therefore we usually refill the rear whenever it gets low. Just don't like standing there holding the nozzle.
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Old 08-31-2020, 08:30 PM   #17
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Quote:
Originally Posted by Judge View Post
And while I was at it, I thought I would post this as well. It mirrors what I had posted in another thread when someone thought they had a problem because the pump would kick off and they had to lower the flow rate out of the nozzle at a truck stop:

Diesel fuel dispensing nozzle fill rate:

Your vehicle has a fuel fill pipe that is able
to accept fuel up to 20 gal (76 L) per
minute from an 1.2 in (30 mm)
fuel-dispensing nozzle. Pumping fuel at
greater flow rates may result in premature
nozzle shut-off or spit back.
Truck stops have pumps and nozzles
designed for larger, heavy-duty trucks.
When refueling at truck stops: if the nozzle
shuts off repeatedly when refueling, wait
5–10 seconds; then use a slower rate of
flow, do not depress the nozzle trigger as
far.



For a standard F-550 truck, the plumbing may be different than the Omni Magnitude. I can tell you it won't take 20 gallons per minute. There is a 90 degree bend in the fuel filling pipe in the Omni / Magnitude so it will back up and start foaming at high rates and kick off the pump.
Diesel pumps in the truck lanes have a nozzle that is about 1 3/16 or 1 1/4 inch in diameter and the pumps have a flow rate of approx 60 gallons per minutes. The diesel pumps on the car side have a nozzle size of 15/16 inch and the pumps have an EPA limited flow rate of 10 gallons per minute.

To put 75 gallons in my rig (3/4 tank) it takes about 2 minutes on the truck side and half a day (seems like) on the car side (about 9 minutes).
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