How low can the fuel level be and still safely operate a Monaco diesel pusher?

[TDaleABQ]

Hello all, 

I have a 2007 Monaco Knight SKT that I bought new.  I will never replace her.  Early on I was traveling east on I40 from Flagstaff, AZ to Albuquerque, NM.  My fuel gauge has never been accurate and I was told to only rely on the Aladdin.  I was between Flag and Winslow.  The Aladdin was registering 35 gallons of fuel and the gauge was on Empty.  I was going to refuel in Winslow about 30 miles to go when the engine stopped.  Luckily I had Good Sam and was brought out 5 gallons to get into Winslow.  The tank only took 65 gallons out of a 100 gallon tank.  I contacted Monaco at the time and was told that the sump pump does not go all the way down to the bottom of the tank and that was normal.  I have always wondered if this is true and has that happened to anyone else.  Look forward to your answers.  Be safe.

TDale, ABQ,NM

[Guest Ray Davis]

Hi Tim,   To bad you wasn't around when Bill D ( founder ) was here.  He warned us often to fill up at 1/2 tank or sooner.  Being on the side of the hiway is not fun.

I don't trust my gauge either and yes it happens to others too, happened to me about 15 or 20 mi from home. I thought I got this, it's low, but we're practically home.

It's a lesson neither of us ( you & me ) will forget soon, I hope.

[DavidL]

Running out with 35 gallons in the tank?  That doesn't sound right at all.  5 gallons? Sure.  Are you sure all measurements were accurate?  And that 65 gallons filled it and not just a gas burp that shutoff the filler?

The Generator doesn't go to the bottom...but the fuel pickup for the motor sure should.

Anyway, don't know about your specific rig, but I would not be happy.  That's false advertisement ie: 100 gallon tank.  Or Fuel Range = X miles.

Now, with that said, I just today replaced my fuel sender in my boat...the issue is it uses capacitance sensing to detect level.  And back when it was originally calibrated, no ethanol was in the fuel.  Now there is and that will let the gauge show 1/2 tank and actually be empty.  New sender recalibrates with the Ethanol percent on each fill up so it's now flexible with the gas quality (or less than quality).  I assume your rig is a diesel so that story doesn't apply.

If my RV had the problem, I would be fixing it.  Here is who built the sensor for my boat:  http://www.centroidproducts.com/  they build custom sensors based on tank depth height and the electrical needs of the gauges.  Took two weeks to get some custom ones built.  About $80 each.

My Newmar had a fuel sender issue...just waited till the tank was low on fuel, and then popped the old sender out in one of the baggage compartments had a port hole just to service the fuel sender.  30 minute job and $125 sender and now accurate.

 

EDIT: why lookie that...they have a document specific to Monacos:  http://www.centroidproducts.com/zTroubleshootingMonaco.pdf

Edited August 13, 2022 by DavidL

[Ivan K]

Curious where the Aladdin takes it's measurements vs the gauge, or is it a calculated number not taking a generator use into account. I have a Triptek and the signal branches off the same sender wire but is calibrated for 150 gal stock tank. I, for one, learned to trust the gauge. Until I don't, I guess.. I had the red light come on with no gas station in sight and gauge on empty in middle of nowhere Idaho. When I finally made it to refuel, the 200 gal tank took around 180 gallons. I can imagine 20 gallons in that footprint just makes the bottom wet, figuratively of course but probably would not want to have the bottom sucked in anyway. In hindsight, it confirmed several things for me and I only wish I had tried to see the Triptek reading and tested the generator shutdown level but that just wasn't a priority at that time, surviving the wife was. About 10% of dead space would sort of be acceptable to me and I never actually ran out but over 30% sounds too much of an error and a short pickup tube. My sender is adjustable and I know that it doesn't show full when it should, about 1/8 less and I don't want to mess with potentially disturbing the verified near empty reading. But normally I'll start looking for an EFS discount station at about half tank just like others said.

Regardless, looks like your Aladin was right wherever it gets it's reading from and the pickup needs lengthening, if that's a word... The gauge is an other story addressed above. 

[mmartinhouse]

Sad to say we also belong to that club.  Tank showed about 1/4, Aladdin said could go 154, trying to save a few pennies we were headed to the next exit that was over state line.  All of a sudden said 50 miles then zero.  Outside temps in the 90's, on the side of the road with 18 wheelers wizzing by.  Had Coach net.  Brought gas and tried multiple times to get it started.  Was just about to quit when it started.  Don't ever want to repeat that again.  We fill up now when it gets just below 1/2.  Recently had to replace the sending unit sensor, but still don't trust the gauge, and fill up long before gets to 1/4.

[Old Dog]

Not sure if this has already been addressed but and kind of off topic but... the fuel from the tank also cools the ECM, at least on my ISX 525hp. In those cases you should keep the tank above half when running in high ambient temps or heavy loads.

If you've ever fueled up when temps are a 100+ the fuel tank and fuel gets HOT from the return fuel which is then used to "cool" the ecm. Wouldn't be surprised if that has caused a few ecm failures since electronics don't like temps over 120 degrees. 

More fuel, cooler fuel temps and better cooling. Food for thought.

High temps also killed my TV mounted in the front cabinets, that front cap area has no insulation and gets super hot. The locals in AZ won't store televisions in the garage because the temps in the summer kill them.

[96 EVO]

Ran mine down to 1/4 tank once (trying to get out of CAL before fueling up), I was nervous!!

[Guest Ray Davis]

9 hours ago, Old Dog said:

the fuel from the tank also cools the ECM,

Many cars & trucks today have an elect fuel pump inside the tank.   Fuel cools the pump and wiring.   

Empty tanks, not good,   full tanks good.

9 hours ago, Old Dog said:

electronics don't like temps over 120 degrees.

I don't either.

[lake49068]

My Neptune has a 75 gallon tank that trapped me on our first long trip.  It should get over 500 miles on a full tank but didn't come close.  Seems the filler pipe configuration causes the fuel pump to kick off way too early.  I use a flashlight with every fill and continue pumping until the fuel gets near the top of the fill neck.  Usually adds another 10-12 gallons, I reset one of the trip odometers and refill at around 450-500 miles.  The fuel "gage" is just a guide, not gospel. 

[dl_racing427]

My fuel gauge used to read correctly until I started driving.  The fuel would apparently foam and cause the Centronics capacitive pickup to read full all the time.
I checked the resistance range of the gauge, and replaced the sender with an old-fashioned float-type.
I adjusted the float arm to show empty just above the tank bottom.
It's much more accurate now, but I still try not to run it down below 1/4 tank on my 130 gallon tank.

[RWHenhouse]

I recently drove my 2004 Safari Panther until the gauge was showing 1/8".  (Travelling in NE British Columbia, pumps at planned stop were down.)  Hot day for that part of the world, temps 85-90F.  Reached truck stop and filled up. Then, engine (Cat C12) would not start.  Turned over but would not fire.  Tried bleeding water separator (no air, fuel clean), removed all power in an effort to reset ECM if that was the problem, all to no avail.  It was getting late so pulled the unit away from the pumps.  Next day changed both fuel filters and primed.  Old filters were clean.  ECM was throwing 2 codes - one for idle shutdown, which happens when I leave it idling too long; and one for low ECM battery - I had had to boost it about 2 months previously.  Ended up loading it up and hauling it 300 miles to the Kenworth dealership near my home.  It sat in their yard for a week; they towed it into a bay, and it started up on second attempt without doing anything to it.  They spent 2 days trying to figure out what the failure might of been, came up empty. Fuel pressure good, grounds good, ECM wiring good, etc. Tough to diagnose something that refuses to fail.  After reading Old Dog's post I'm starting to wonder if hot fuel may have triggered my problem.

[jacwjames]

Not long after we bought our coach I was parked at the storage yard doing some work on the coach running the generator.  Fuel gauge read over 1/2 full.  Generator died.  Pretty much figured it was low fuel so drove to the fueling station and pumped 100 gallons of fuel into a 128 gallon tank, so I know how low I can go for the generator to continue to run.  Also know that i don't want to get that low since I really don't know where the engine pickup is located. 

I tried to pull my engine pickup tube but too long without bending so I didn't go any further but it might be worth knowing how low it goes. 

My fuel gauge is not accurate at all even after calibrating it. 

In 2013 I purchased a Silverleaf VMSpc.  I set up a fuel tank monitor which uses fuel consumption from ECM, tank size is 128 gallon.  So it shows me fuel tank level in gallons and range I can drive.  This has proven to be very accurate, probably within 1%.  The biggest issue is if the coach is leaning while fueling and I can't completely fill. 

Edited August 14, 2022 by jacwjames

[MyronTruex]

Any chance they reversed the generator and engine pickup lines" That would be a simple mistake to make. 

 

[jacwjames]

41 minutes ago, myrontruex said:

Any chance they reversed the generator and engine pickup lines" That would be a simple mistake to make. 

 

Since the generator ran out of fuel with 100 gallons left in the tank & I could still start and drive the coach ~15 miles to fill up tells me they didn't reverse the pickup tubes.  Just don't know how low the engine pickup tube goes. 

[Dr4Film]

I have the most experience with fuel tank capacity on my previous 2002 Windsor. Not so much on my current 2006 Dynasty.

With the Windsor I ran out of fuel once but was lucky enough to have enough momentum to roll into a fueling station right up to a diesel pump. I pumped 101 gallons of fuel into a 128-gallon capacity tank. Therefore, there are 27 gallons of fuel unusable.

The generator and Aqua-Hot both seem to stop working around the same time. When that happens, I usually pump in about 85 gallons of diesel.

I haven't had the Dynasty that long to figure out what happens when BUT trust me I WON"T be running out of diesel ever again. When it happens to you once shame on the fuel gauge but if it happens to you a second time shame on YOU!

 

[jacwjames]

19 minutes ago, Dr4Film said:

 I pumped 101 gallons of fuel into a 128-gallon capacity tank. Therefore, there are 27 gallons of fuel unusable.

 

Yikes, that means when I pumped 100 gallons I was close.  Thanks for letting me know on this. 

I may go ahead and try and pull my pickup tube and check. 

[ok-rver]

Two days ago I picket up a clean 55 gallon drum for a planed project. My fuel gage seems to be a reliable on how much it takes to fill the take. at 3/8 full, about 60 gallons on a 100 gal tank with 85 gallon tank capacity at the bottom of the fill neck, level MH. Currently estimate of 30 gallons in the tank. Monday, I am re-plumbing my FASS system to pump ALL of the fuel out of my tank into the drum. I plan on pumping about 5 gallons at a time with generator running to get an idea of where the generator will shut off. Once I have established that point on the gage, recorded by a picture as my memory is not like it use to be, I will pump until the pump pickup sucks air. Another picture. I will measure the height of fuel in the drum to estimate the number of gallons in the drum. I will then tilt the MH towards the side of the pick up and pump out as much as I can. Another height measurement for an idea of how much in the tank is not usable.  At this angle, there will should be less than 5 gallons in the tank.  Not sure if I will be able to extend a wire with a cloth into the tank to see if any gunk on bottom. My engine standpipe is welded in place. The only easy way to measure would be to remove the top fitting and use a flexible wire with a small hook to maybe measure the length. 

Then re-plumbing hoses, I will pump the diesel back into the tank assuming that what is in the drum looks good.  I have 10k miles on the original FASS filters with pressure down from 19 psi originally to 15-16s psi. i will change out both filters. The FASS pump when in run position of hoses will pressures/bleed air from the CAPS system and I should be ready to go for the main.

Electric fuel pump on generator will re-prime system. it would be a good time to change the generator filter while the filter is pretty empty. There is a spice on the suction and return line suppling the generator. It drips a very small amount of diesel no matter what I do to the hose/barbed splices/clamps. I may also run a single continuous line from the tank to the generator while the line is empty. I think this is letting air into the line and requires an extended pre-start run of the gen electric fuel pump to get it to keep running.

Diesel is down to around $4 in Tulsa so a 10 mile run to Costco, a fill up, and some calculations using the amount in the drum plus the fill amount will give me an estimate of how many gallons until sucking air.

Looking for input

[MyronTruex]

As a side note, I extended my generator fuel pickup. At 1/2 tank it would die, especially in long curves that moved the fuel away. I was able to get to my tank sensors easily.

[Dr4Film]

1 hour ago, jacwjames said:

Yikes, that means when I pumped 100 gallons I was close.  Thanks for letting me know on this. 

I may go ahead and try and pull my pickup tube and check. 

Personally, my feeling is that when they installed the tanks and fuel pickups there wasn't any standard process or method that they used. Yours could very well be different than the 2002 Windsor I owned.

It never was a problem once I figured out approximately how the dash analog fuel gauge reacted where it became critical to prevent the generator and Aqua-Hot systems from shutting down.

When we would travel in the Windsor starting out with a full tank, we could overnight the first night but after the second full day of travel I would always fill up with diesel BEFORE stopping for the night. With that method we were always assured that the Aqua-Hot and generator would have enough fuel for that evening and the next morning before getting back on the road again.

[cbr046]

After I ran out of fuel when I filled up there was 16 gal unaccounted for.  I figured in the last fillup the coach was sitting at an angle with an air pocket in the RH side of the tank while filling on the LH side.  Now, if I'm shooting for full range of the tank, I'll use the LR jack to tilt the coach while refueling. 

Oh yeah, the tank said 3/8ths when the low fuel light came on in the middle of nowhere.

- bob

[RoadTripper2084]

On my 1997 Dynasty with 130 gallon diesel tank, the owner's manual has this to say about useable capacity:

Quote

The diesel fuel tank is mounted transversely in the coach.
The fuel line connections and fuel gauge sender can be accessed by opening or removing the panel where the fuel filler door is located.

Note On Tank Capacities: The engine fuel system pumps more fuel to the engine than is needed, Fuel Tank and the unused fuel is returned to the tank. The fuel is heated by the engine and when it returns to the tank it expands and foams. All fuel tanks are engineered to allow for thermal expansion of the fuel, and for foaming. Monaco's fuel tanks also have flat bottoms to more efficientlv utilize the available space, therefore the pickup tube cannot draw all the fuel from the tank. For these reasons the usable capacity of the tank will be less than the rated capacity, which is based on total interior volume. The actual usable capacity will be approximately 35 gallons less than the rated volume for any given fuel tank.

 

Edited August 15, 2022 by RoadTripper2084

[TDaleABQ]

Boom.  That makes perfect sense.  Now I wish I had the 130 gallon tank.  I have read and re-read my manual many times and must have over looked that.

Again,  THANK YOU for answering the mystery.  Happy trails to you.

T. Dale, ABQ, NM

[jacwjames]

Hmmm

My brochure says 128 gallon tank, which is what I set my tank minder on the Silverleaf at.

I just checked my manual and it says 118 gallon tank. 

Scary since I have pumped 100 gallons into the tank.  Will have to rethink that and start targeting 90 gallon max consumed.

[dandick66]

I ran mine out of fuel 4 years ago.  Fortunately, it ran out in the driveway.   I knew I was low, but didn’t think it was that low.  I added 5 gallons and got it started and drove to get fuel 11 miles away.  It took 98 gallons.  Tank is 100 gallons, so it definitely is accurate.  Yes, the low fuel light came on, but I “calculated” that I should have had plenty of fuel to make it home.

I’ll never run that low again.  Since then I’ve discovered that I can add 12-15 gallons more fuel after the pump cuts off.  Something else I do is level the coach when I pull up to the pump.  I also track exactly how many miles I’ve driven since refueling.

[David Pratt]

To get the correct and more accurate capacity of your fuel tank use the following formula.

Multiply the Height in inches minus 3/8" X Width in inches minus 3/8" X Length in inches minus 3/8" and then divide the total by 231.

When you measure the height of the tank measure from the bottom of where the filler pipe enters the tank or at the top of the filler tube if you can get that much fuel in the tank. The reason to subtract the 3/8" from each total is to adjust for the wall thickness of the tank This will give you the the INTERNAL CAPACITY of your fuel tank.