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Topic: Fuel Tank Vent Plumbing - Was fuel leak....2002 U320 (Read 400 times) previous topic - next topic

Fuel Tank Vent Plumbing - Was fuel leak....2002 U320

A lot has come to light in my search for the source of my fuel smell and probable leak.  After now over 8 hours behind the scope, probing and hunting as well as studying the lines and connections, here are my findings and conclusions....

Observations and issues:

Tank Drawing A-8195 Rev B is incorrect and does not reflect a vent port or external connection to the outside.  Tanks as-built and installed has a vent port (my notes on PDF).

Per conversations with many "wiser than me", all stated a vent line should come from each tank to a "T" and then exit the coach....a logical and functional arrangement.

Scope and other investigation indicates a seepage (very old) that has resulted in a damp spot in the dust and dirt on the main tank, lower top just below the radius near the vent port. 

Visual indicates long term fuel residue at the main tank vent elbow fitting and runoff down the side (noted above).

Vent port from main tank is cross connected to a "T" fitting at vent port on DS fill/return tank.

Opposite end of "T" fitting on DS Fill/return tank has Rollover Valve installed on it's side and then ported to the outside via a vent line.

Entire vent plumbing arrangement is non-functional as installed and will create excess pressure in the top of the main tank, especially when tanks are filled from the driver's side as there is no clear path for venting once the fuel level rises above the "tank to tank" connection.

Rollover valve is always "closed" )except while under external pressure on vent line) as it is on it's side (proven by pressure and vacuum testing of line and tanks).

Corrections that must be made......

Tank will have to be pulled and rollover valves installed vertically (proper orientation) on each tank vent port.

Rollover valve vents will then be individually plumbed to a "T" fitting at the bulkhead and then out to provide proper, unrestricted venting.  In the event of an "incident', both valve will close properly and prevent a fuel spill.

I have attached a "cobbled up" drawing of my current condition and proposed (determined by logic and physics) solution.  Also a few pictures of the main tank vent fitting as well as the DS Fill/return tank plumbing arrangement....

This discovery probably answers why filling from the DS was a slow and tedious process to avoid blow back and spillage.  The photo of the main tank vent indicates possible seepage from the hose to elbow threads and/or a possible casting defect in the elbow...cant get a clear shot with the scope.....

Anyway, anyone with the main/pony tank arrangement should inspect for proper plumbing as clearly my installation is not functional on many levels......

Standing by for comment and observations....  YMMV...

2002 U320
3620 PBDS
Build 5985
2021 Equinox Toad
Motorcade 19006 & all those "other" clubs too!

Re: Fuel Tank Vent Plumbing - Was fuel leak....2002 U320

Reply #1 –
Quote from: rusczyk56 –
Standing by for comment and observations....
This is, to me, a very interesting post because I don't recall ever hearing about Foretravel coaches with two fuel tanks.

Some of your photos are kinda blurry - hard to tell what I'm supposed to be seeing.

Sounds like you have pinpointed the problems, and have a solution, which certainly will benefit other Forum members.  ^.^d

I have a question: Why two tanks?  I mean, why not one tank shaped to fit the available space?  It's hard for me to visualize how these two tanks fit into your coach's structure, so excuse the question if the answer seems obvious to you.

What is the total capacity of both tanks combined?

1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Fuel Tank Vent Plumbing - Was fuel leak....2002 U320

Reply #2 –
Tanks....  Well, another "motorhome builder" work around.  In 2002 when the floor support structure design changed, it included two trusses that run from the front bulkhead to the back.  This resulted in needed to lower part of the tank to fit under the trusses.  So, the main tank is 174 gallons and has a dropped center section.  The tank is about 2/3rds the width of the coach.  Now why that wasn't enough (only by 9 gallons), I don't know.

The second tank (9 gallons) is on the driver's side in the bay with the AH and serves as the DS fueling port as well as where all the fuel return lines terminate.  The "cobbled" drawing is more or less a "top down" view where the big tank is on the left and the "pony tank" is on the right.  There is a 2 1/2 inch line that drops out of the bottom of the pony tank and into the side of the main tank. 

I sort of understand the arrangement for the dual fill, but I have also owned and seen coaches with dual fills that were nothing more than a long neck from the tank that is center mounted. 

I am sure some "engineer" who minored in fluid dynamics had some sort of an epiphany and came up with what we have.

I am owner 3 for this coach but it is clear there has been seepage for a long time.  Nothing wet or ponding, just enough to make a stink and keep things interesting.  Anyone who understands venting and why rollover valves exist would ask "WHAT WERE THEY THINKING?".  I have some experience dealing with fuel storage and stationary generators and this is not how it works.

So, now on the "wait list" for Keith to have a full on "fuel tank-ectomy" and while in there, replace all the hoses and fittings.  As they say, in for a dime, in for a dollar....

Keep them question comin in!
2002 U320
3620 PBDS
Build 5985
2021 Equinox Toad
Motorcade 19006 & all those "other" clubs too!

Re: Fuel Tank Vent Plumbing - Was fuel leak....2002 U320

Reply #3 –
I have to agree - all that extra expense, fabrication, and plumbing complication to gain an additional 9 gallons?  That's crazy.

As for adding the extra tank to provide dual fillers - I would have told them don't bother if it's only going to hold 9 gallons.  Our U280 only has one filler, on the passenger side, which has always been an irritation to me but only because it is on the wrong side.  I would love to have only a single filler on the driver side, and never have to screw around with using the slave pump at the truck stops.
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Fuel Tank Vent Plumbing - Was fuel leak....2002 U320

Reply #4 –
Quote from: rusczyk56 –
Tanks....  Well, another "motorhome builder" work around.  In 2002 when the floor support structure design changed, it included two trusses that run from the front bulkhead to the back.  This resulted in needed to lower part of the tank to fit under the trusses.  So, the main tank is 174 gallons and has a dropped center section.  The tank is about 2/3rds the width of the coach.  Now why that wasn't enough (only by 9 gallons), I don't know.

The second tank (9 gallons) is on the driver's side in the bay with the AH and serves as the DS fueling port as well as where all the fuel return lines terminate.  The "cobbled" drawing is more or less a "top down" view where the big tank is on the left and the "pony tank" is on the right.  There is a 2 1/2 inch line that drops out of the bottom of the pony tank and into the side of the main tank. 

I sort of understand the arrangement for the dual fill, but I have also owned and seen coaches with dual fills that were nothing more than a long neck from the tank that is center mounted. 

This is fascinating, and here's why:

Early on in our ownership of our '03, we had a couple of stalls pulling into a truck stop with just below 3/8 tank of fuel.  It wasn't every time, but enough that we asked Foretravel about it.  Discovered it was the particular baffle design used in that fuel tank.

Turns out there were at least 5 different tank design revisions for the 2003 model year, including multiple different baffle and fuel pick-up configurations.  So apparently beginning in 2002 and through 2003, fuel tank configurations and designs vary a lot between coaches and even Foretravel might not know which you have unless they can get a serial number off the tank or scope it.

At one point we had the (paper) drawings of all 5 versions for 2003  I don't know if we gave all of them to Dan when he bought the coach or if some are still floating around in our files somewhere.  I'll look (I don't immediately see them in my electronic files, and it looks like I've only uploaded one version to the forum library)

ETA - found the paper copies.  Will scan Scanned in and put in Schematics.  Note they reused part numbers even though they changed internal designs.
Learn every day, but especially from the experiences of others. It's cheaper!  - John C. Bogle

2000 U320 36' non-slide / WildEBeest Rescue
2003 U320

Re: Fuel Tank Vent Plumbing - Was fuel leak....2002 U320

Reply #5 –
Quote from: Michelle –
we had a couple of stalls pulling into a truck stop with just below 3/8 tank of fuel.  It wasn't every time, but enough that we asked Foretravel about it.  Discovered it was the particular baffle design used in that fuel tank.

I wonder if the baffles prevented the fuel from transferring between compartments at the bottom?  Tank baffles I am familiar with provide compartmentalization to prevent fluid from sloshing but have openings at the bottom to allow it to transfer gradually between the compartments.
George Mann
2002 U320 #5934
2017 Rubicon
2013 BMW GS
Waterford MI

Re: Fuel Tank Vent Plumbing - Was fuel leak....2002 U320

Reply #6 –
Quote from: Chuck & Jeannie –
I have to agree - all that extra expense, fabrication, and plumbing complication to gain an additional 9 gallons?  That's crazy.

I have these tanks and I don't think the intent was solely to gain 9 gallons.  In fact I believe the book for my coach lists the fuel capacity at 174 which totally ignores the 9 extra gallons in the port side (mini) tank.  I think the main reason was for dual side fill and while they were at it they just maximized the use of extra space in the Aquahot bay.  I actually think it's quite elegant.  I do wonder how the 2 1/2" coupler between the two works since it's completely inaccessible (without removing the Aquahot).  One drawback I can think of is with a full fuel tank the (considerable) load is not balanced side to side and puts significantly more weight on the starboard side of the coach.
George Mann
2002 U320 #5934
2017 Rubicon
2013 BMW GS
Waterford MI

Re: Fuel Tank Vent Plumbing - Was fuel leak....2002 U320

Reply #7 –
Quote from: rusczyk56 –
Entire vent plumbing arrangement is non-functional as installed and will create excess pressure in the top of the main tank, especially when tanks are filled from the driver's side as there is no clear path for venting once the fuel level rises above the "tank to tank" connection.
Standing by for comment and observations....  YMMV...

I wonder if your vent is simply not functional.  I have had no problems filling the tanks to the point of overflow from either side of the coach.  I will try to look at my fuel lines more closely to see if they are as you describe.  I'm assuming there are 3 supply lines (main engine, AquaHot and generator) and 3 return lines and two vent lines.  Four taps on the port side and four more on the starboard side (pony tank)  Is this what you have found?
George Mann
2002 U320 #5934
2017 Rubicon
2013 BMW GS
Waterford MI

Re: Fuel Tank Vent Plumbing - Was fuel leak....2002 U320

Reply #8 –
I know that the vent line is in the middle of the tank and I have never checked it out but I thought
there is a valve at the top that lets air in and out but won't let liquid out as I fill my tank as full as
I can and never had fuel come out.
Peter and Frieda Morin
1999 36ft. U320 Foretravel
Build # 5436
1998 Suzuki Sidekick Sport

Re: Fuel Tank Vent Plumbing - Was fuel leak....2002 U320

Reply #9 –
OP here....

Geodmann...  The port arrangement (see previously posted PDF) is as follows:

Main Tank:  Fill pipe, Eng, Gen, AH feeds (tubed to near bottom of tank), vent port on top of tank in rear corner and 2 1/2 inch pipe mid tank sidewall on DS for tank to tank flow.

Pony Tank:  Fill pipe, returns from Eng, Gen and AH, Vent port (not documented in on FT DWG), and 2 1/2 inch drop pipe for tank to tank transfer.......

Moving forward.....

So, tanks before 2002 are of a different configuration due to structural and other equipment location changes that took place for the 2002 and up builds.

The baffles are not the issue related to the improper venting of my unit though it may explain the possibility of fuel hitting the corner of the main tank where the vent nipple lives.  I did scope the inside of the tank and there is clearly a baffle of some sort shielding the vent nipple.

Also the baffling has nothing to do with the fuel flow from the pony tank (9 gal. DS Fill and return tank) as the fuel from that tank flows through a dedicated 2 1/2 inch drop pipe and mates to a 2 1/2 inch pipe on the side of the main tank about mid-way down the side.  The inability for the main tank to vent once the fuel level is past the pipe level is an issue that I previously noted.

Where I am at now is to attempt to get a long (about 2 feet) 3/8 inch drive extension with a crow's foot and see if the hose fitting on the main tank vent 90 degree fitting (yes, should be a rollover there) is possibly loose.  If I find I can tighten it, and my "smell" goes away, I have an alternate plan for the main tank venting....at least temporarily.

I will disconnect the main tank vent hose from the pony tank T fitting (cap open end on T) and pull the hose back to the pass side and install a vertically oriented roll over valve on it and then route the vent line off the valve to one of the LP bay vent holes.  Worst case is I at least get the possible pressure out of the main tank temporarily until a proper fix can be completed....  I have another idea that "could" result in a permanent fix but I have to give it more thought as it does require the removed of the T on the top of the pony tank as well as the removal and reinstallation of the generator return elbow....  But, first, need to check for loose fitting...

Fact is there are so many variables involved across the various builds.  I am convinced somebody "screwed up" on my build (Late Friday, hose T not available, rollover vents in short supply, inexperienced employee,...who knows?).  No matter what, it could never work properly.  The only saving grace is short of the bus ending up standing upright on it rear, the valve would remain closed....some consolation.........LOL...NOT!

In any case, I would strongly suggest anyone with the two tank arrangement inspect their venting and ensure rollover valves are installed on the tops of both tanks (or at least the top of the main tank,), upright and properly vented out.  There is a possible alternate scenario where both tanks are vented to a T and somehow the outbound side of the T has the rollover valve installed properly oriented (i.e. upright) and then vented to the outside. 



2002 U320
3620 PBDS
Build 5985
2021 Equinox Toad
Motorcade 19006 & all those "other" clubs too!