I ran into this issue on my inaugural trip last year when I reached a quarter tank, which turned into an hour of troubleshooting before bleeding it. I have a few questions:
1- How does this system work? What tells the generator to shut off at a 1/4 tank fuel level? Is it a solenoid ? ECU controlled? Or??
2- Next, where is this located?
3- Lastly, has anyone overridden this? I understand why you may not want to do this, but if you're 20 miles from your fuel station and its 100 degrees out, I know I'll have enough fuel to make it but would like to not lose the AC.
If not mistaken, the generator has a pickup tube inside the tank that is higher up in the tank, so the generator will be sucking air when you havre 1/4 tank of fuel left. This prevents being stranded if boondocking and you run the tank dry. Foretravels have generous size fuel tanks. My habit is to fill, or start looking for a place to fill, at 1/2 tank.
Fact....
An elevated pickup tube compared to the engine.
Like others have said it is the length of the pick up tube. You can slip the tank out and install a new pick up tube that reaches right to the bottom like the main engine pick up. You might be able to "T" into the main engine fuel supply line with an electronic valve that you can open in an emergency. Now this could starve the engine injector pump or???
Mike
Our late Rockwood had the generator fuel tapped off the engine fuel line. If you're worried about not being able to run your AC carry a sealed 5 gallon can of diesel.
Or a driver can fuel up when ,while there is still 1/2 or just shy of that amt of fuel left in the tank. That way I never have to give thought to "am I getting close". It"s just as cheap per mile to run on a full tank vs a near empty tank and sometimes cheaper.
Good to know, thanks all!
Plus the 1/2 full method would keep return fuel temps down a bit. I've done no test to see by how much but in theory the fuel temp should be lower given there being more fuel in the tank.
I went to the military surplus store and purchased two brown five gallon plastic water carriers for a reasonable price. I fill one with water and one with fuel. I carry them in the outside vented storage compartment. There is a controversy concerning carrying fuel inside a compartment not properly vented. I guess it's up to the coach owner to decide whether to carry fuel or not. I'm a big believer in the two is one, one is none mentality. Which means it's important to me to know I have a five gallon backup container of fuel in case the fuel gauge is incorrect or I incur a leak in the fuel tank. Not trying to tell people what to do, just sharing what I do, as I like being out in the rural area campgrounds far from civilization. That has a price, which means planning ahead for a potential problem. The military trained me that Proper Planning Prevents Piss Poor Performance.
Diagram below of a 150 gallon fuel tank. Not sure what model year exactly. Filler neck on both ends so Unicoach. You can see there are 4 tubes hanging down from the top of the tank. 3 tubes are shown to be 2.5" above the bottom, while one goes nearly all the way to bottom. I assume the higher mounted pickup tube is for the generator fuel supply line. A commonly quoted "fact" on this Forum is that the generator will start sucking air when fuel in tank reaches 1/4 full. On a 150 gallon tank, 1/4 full would be roughly 37 gallons left at bottom. From the diagram dimensions, looks like that tank would hold roughly 6 gallons per inch. A fuel pickup tube sucking air and hanging 2.5" from the tank bottom would leave only approximately 15 gallons in the tank - considerably less than 1/4 of the full capacity.
What does this all mean? I don't know. Food for thought. I try to always fill up at no less than 1/2 tank, so I don't really care.
PS: I just dropped a copy of this diagram in the Forum Library where it will be available for future reference. Any of our members who might have copies of similar "rare" Foretravel documents should do the same.
A well stocked library helps increase the value of our Forum!
Good diagram Chuck, thanks. Looks like I won't be making any changes to it, that is a lot of work to lengthen the tubes. I tow a gasser but one day I am going to tow my cummins, that has an aux tank in the bed which would be ideal for a backup.
When I had the Monaco I ran out of fuel one day and found out the fuel pick up for the engine
didn't go to the bottom of the tank. You were to run out of fuel with 34 gallons left. I asked why
and they said incase you get water in the fuel. My thought was if I pick up water I want to know
right away not have gallons of water in the tank. I pulled the tank, built a sump and put the pickup
below the bottom of the tank. I also put a drain valve in the bottom of the sump so every time
I serviced the engine I would drain a little fuel to see if there was any contaminates in the fuel.
Chuck,
Good diagram. Yes, that is a common "fact" on the forum. The A-4840 drawing was dated 1992 but the stamp says 1997. No 1992 Foretravel 36' had fillers on both sides that I'm aware of as the generator is in the way so the fuel tank only goes part way across. Wonder if this is different on a 40 foot coach? Don't think I would feel secure with only 12 gallons in the tank. Yes, food for thought.
With a very warm fuel tank, best to keep at least half full unless you have a fuel cooler in the return line.
Grey Wolff,
I see you have a gasoline engine coach. Having a container of gasoline on board is a lot different than diesel. In our U300's vented fuel tank/propane tank compartment, there is no room for a container. Probably different in your coach. In case of an accident, I don't think I would be happy with a plastic container of gasoline next to the exit if that is the location.
Pierce
Old Guy,
I'm not sure how accurate the salespeople are about the reason for the short pickup. I had a Volvo salesman tell me that the reason VW letters were on the side of the diesel engine in the Volvo was because Volvo made so many diesel engines that VW used them. The fact was VW supplied their diesel van engine to Volvo.
Pierce
Our '93 40' U280 is probably the same tank-wise as your coach - it only goes part way across. Since my tank is not as long as the one in the diagram, but still holds 150 gallons, it is obviously a different shape. My tank is 25.5" tall (same as tank in the diagram) but wider at 21", and shorter (in length) at 66". Coincidentally, my tank also holds approximately 6 gallons per inch when I measure fuel remaining with a dipstick.
I found out about the high fuel pickup from the tech.
Running low on fuel is never a good idea. Some fuel is always returned to tank during engine operation. Return fuel can be very warm and the design is remove heat by mixing the warm fuel with cooler fuel in the fuel tank. Low fuel level work like a heater, sending new fuel to engines much warmer than it should be.
That is in addition to killing generator and sucking air into gen fuel system. And for sure you never want to run your main engine out of fuel, not only leaving your stranded, but maybe impossible to easily start engine, stressing starter & battery. So, there is no guarantee on bottom fuel level in tank. Don't forget the bottom of the fuel tank may have water & debris, causing another unwanted problem.
Bad habit to run tank low. Think of coach breakdown on side of road where low fuel contributes to additional problems.
Think of generator running on air as notice that you are too low on fuel. Fix that problem by stopping earlier to add fuel.
1. Totally agree.
2. In the case of the Foretravel tank illustrated in the diagram I posted in Reply #9, you will notice that the fuel pickup tube for the big engine hangs down from the top of the tank. According to the diagram. the open end of the tube is only 3/8" off the bottom of the tank. So in this case, it doesn't matter how much fuel is in the tank, because the fuel is
always being sucked off the bottom. If there is any water & debris in the tank, it could be pulled into the fuel pickup at any time regardless of fuel level. Which is why it is so important to use only high quality fuel filters and replace them on a regular basis.
Yes, does not make any difference if the tank is full or almost empty, any algae, water or other foreign debris are just as likely to be sucked up but if the owner checks the primary see through bottom, it will be seen. Probably a good idea to drive for a few miles after fueling and then check the sight glass.
Some filters have a water sensor but they need an amplifier to trigger any alarm or light.
Polishing the fuel is the biggest waste of money possible. A clean tank is only good until the next time fuel is added. If algae is seen, change filter and add biocide to the tank. It will kill the algae and all remaining will be caught in the filters of the main engine and generator.
Pierce