New to me SuperNova - Question about the fuel tanks

[Madkel]

Just bought a 2008 SuperNova 6331 with 44K on the odometer.
Picked it up in Salt Lake City, Utah and drove it 700 miles to get home.
All in all it ran great.
Not a speed demon and it takes a bit to get it off of the line, but I really like the cab configuration and the solid feeling of the International 4200 Chassie.
However, it will never win any races.

For the drive home, we started with 1/3 a tank based upon the fuel gauge. We went to Costco to fuel the passenger tank and put in about 50 gallons. started to drive off and noticed that the gauge still registered 1/3 of a tank.
Got back into line and filled up the drivers tank. It took about 50 gallons.
Great, now that we are full, let's start the drive home.

During the initial drive, the fuel gauge would fluctuate between 3/4 and 7/8 of a tank

Drove about 300 miles and wanted to refill again due to the much lower cost of diesel in Utah. Went to fill the drivers tank and it took 6 gallons. then I filled the passenger tank and it took 38 gallons. So, about 7 miles per gallon with a bit of generator usage too.

Drove the balance of way home (400 more miles) and the tank reads just over 1/2. I did dip the tanks and the drivers side is almost full and the passenger side is about 1/2.

My question is: can anybody explain how the tanks are connected and how they work with each other? There is no selector switch in the cab.

I called International to ask about this and was basically told to look it up myself. (THE WORST CUSTOMER RELATIONS I HAVE EVER EXPERIENCED).

The coach came with 2 manuals (one for the VT365 and one for the 4200 chassis) but neither one of them explain how the fuel tanks work with each other.

Can anybody enlighten me on how the tanks operate so I don't over estimate my range?

Thank you.

[Vinnie]

The fuel gauge and engine feed are from the passenger side tank ("primary"). The tanks will cross feed as needed to keep the primary full. Any excess feed to the engine goes back to the tanks. The generator is fed from the driver side tank ("secondary") and appears to have a fixed length suction tube that will only let the genset pull the secondary tank down to about 1/4 before the generator runs out of fuel.

It's a little weird seeing the fuel gauge gain while diving but you kind of get used to it. I have gone well over 900 miles and still had "plenty" if fuel but your mileage may vary.

[Madkel]

Hi Vinnie and thank you for the reply,

Appreciate your help.
Yeah it is a bit weird to see the gauge fluctuate so much as it causes me not to trust the system. I could understand it better if both tanks were at the same level after the 400 mile drive, but to still have the drivers side full and the passenger side below 1/2 while the gauge reads 3/4 (An update from the last post) it causes concern.

I do see how it draws down from the passenger side first, but when will it start feeding from the drivers side? Do you know how that system works? any guidance on who I can reach out to (besides International) to explain that or give me some more confidence?

thanks again.

BTW, just curious, where are you located?

[LTC_R]

Can’t recall where I read it, but the fuel level sensor in in the passenger side tank is supposed to send a signal to a crossover pump in the driver’s side tank when the tanks are at significantly different levels that pumps fuel to the passenger side tank. I distrusted this a lot and it made me crazy. Once while driving I noticed the fuel level going up on the gauge and happened to be right by a rest area so I pulled in. I did a quick dip test of the levels in each tank and they were pretty close to each other. Mine seem to cross level quite frequently so what you described in your post makes me wonder if there might be an issue with your system.

I did have an issue last year where it wouldn’t cross level. Did some research and found the vent tube on the driver tank had a some critter nesting debris in the end that prevented the tank from getting air when the pump tried to cross level. Removal of the vent hose and pushing a piece of wire through it cleared the blockage and I’ve not had a problem since.
__________________
Brian Redmon
LTC, USA, Retired
2008 GS6400, new to me 2014
2008 JK Unlimited toad

[Madkel]

Thank you Sir.
looks like I will need to do some work to check some items.

[LTC_R]

Happy to help. I’ve learned a lot the hard way the past 10 years, but wouldn’t trade it for anything. Reach out if you need some ideas.

[pwerwagn]

Mine seems to wait until the passenger tank is ~1/2 tank. Then it will start transferring from drivers to passenger.

I ordered a gauge/sending unit to drop in the drivers tank. It would make it easier if I can see the level of both. I’ve considered dropping pickups in each tank and setting up my own pump on a switch so I can force it to do what I want if needed.

I had a similar problem to Ltc, the vent hose on my drivers tank was pinched. It was making fuel transfer really slow, slower than the engine was using fuel.

[LTC_R]

Pwerwagn, interested in what sending units you bought and how (if) you installed them. I had a chevy2500 with dual tanks and really liked the control of being able to manage my fuel. I also had a much better understanding of how much fuel I had available. Thanks.

[pwerwagn]

I have built a few trophy truck/rock crawlers and I always use the tanks.inc floatless sending units. I usually buy the 240/33 ohm ones so I can use auto meter gauges. The tanks.inc can be bought in up to 24” depth. I forgot what length I ordered, I think 18”. I can check. I actually bought 2, I was considering putting 2 fuel gauges in the overhead console area just so I can believe them haha.

These are the typical 5 bolt flange.

[SlimTim]

It’s been a while since I’ve posted but I had the 6400 out this weekend and I thought I would check out the forum.

I agree the SN fuel tank set up is a little strange. As posted earlier it is interesting to see your fuel gage go up as you are driving down the road. I think my 6400 starts to transfer from the drivers side tank to the passenger side tank when the passenger tank gets around 1/2 full.

[Madkel]

Hello again.

Just a bit of follow-up on my original post.
Went on a short trip to Ehrenberg Arizona and back.
Filled up the tanks in AZ as it was about $1.70 less per gallon than in my crazy home state. (Over $140.00 in savings = more than a crazy home state).

When I got home (about 300 miles via the long way) the gauge read above the 3/4 line for the fuel tanks. I then dipped the tanks and it appears that they were about the same level. So it appears that whatever issue I had as stated on the original post has not reappeared and the system is working as designed to utilize fuel from both tanks.

When I did refill in AZ, I did use a fuel additive to add cetane and lubricity to the fuel. It might just be my imagination, but the engine did seam to run better and maybe it helped with the transfer pump?

Now, on to other issues.......

thank you.