When we returned from this summers trip I topped off and put coach in storeage. Had not checked for a while as I had knee surgery. Went over y'day and I saw that I had fuel leaking at front left wheel area. Turns out that fuel has expanded and is leaking from fuel cap. Temp was in 70's when I fueled and I fueled in same station to what I believe is the same level. Temp t'day was 40's. Seems odd that fuel would expand under such temps. Will have to go over t'day and spread floor dry to cover spill and determine if I am going to have to withdraw some fuel from tank, I already releveled to lean coach away from filler neck.
Gary B
HI Gary,
Good to see the knee is out and about!
My guess is that may just be a few RV tears after finding out you had considered leaving her behind for another!!! :)
David
Gary,
Does your fill cap have one of those big o-rings that can be replaced?
It may not be the temp. that is causing the leak, if the tank vent is stopped up with a mud dauber or trash it can cause fuel to be pushed out due to the difference in the barometric pressure change.
Just a thought or 2.
Glad you are up and about, Florida is calling your name.
Pamela & Mike
Me, I think y'all wrong, the coach is so happy to have a break, it wet itself :o
Dave M
As far as I can see the cap on the tank is not vented. It is a white plastic with black top locking cap that screws on, I have I have had it for years. There is a small amount of seepage around the sending unit also. I am mystified. For now I covered the area with floor dri and put a plastic tub under the bay front, I hope that fuel has not penetrated the foam in the bay floor.
Gary B
Gary,
While you filled your tank on a 70 degree day, the fuel, coming from an underground tank, was probably around 56 degrees, perhaps even less. Most all liquids expand as the temperature goes up. The cap is not vented but the expansion of the fuel may have pushed it past the seal and put some on the ground if the liquid level was up to the cap after expansion.
You can see the power of an expanding liquid when you put a coke bottle in the freezer for a few minutes but forget it until the next day. Water is an exception as it expands both when heated and frozen.
The non-vented cap is a big reason why I only keep 10-15 gallons in the tank (and 20 gallons H2O in the water tank) while the U300 is at home. 650 additional pounds is a big deal in the mountains here. Not any chance of fresh, moisture laden air entering the tank, condensing and leaving any water in the bottom of the tank. In three years, I have not found any water in the see-through Racor filter bottom and the tank bottom is spotless.
Pierce
Pierce beat me to this as I was typing it but I will leave my post here.
Could be that the fuel vent is blocked and the fuel has expanded just enough to leak out past the fill cap. When I had underground tanks the fuel stayed around 50 deg F. year round. So if you topped off the tank then raised fuel by 40 deg F in a 150 gallon tank you will get an expansion of 2.7 gallons. Then if the coach leaned enough to have the fuel at the cap and it expanded from warming by the fuel return you may have leaked from it. If the vent is blocked you will also have pressurized the tank causing the leak to be worse. Remember, as you know, diesel fuel is like penetrating oil it spreads all over without evaporating and a little goes a long way. Or you have a leak elsewhere. I would remove the cap carefully and look at where the level is. If it's below the neck you will be OK. Then after driving for a while remove the cap an see it you relieve any pressure. I am not familiar with the U300 coaches but this might apply.
Keith
Gary,
If you had my coach, it has more to do with how full the tank was and how level the coach was when stored vs. during fill up.
There are a number of variables:
1. Thermal expansion and contraction of a 150 gallon aluminum fuel tank is a factor:
a. There is roughly 1.2 gallons more room in the tank over a 40 degrees F rise in temperature.
2. Thermal expansion and contraction of 150 gallons of fuel is a factor:
a. There is roughly 2.7 gallons more fuel (by volume) in the tank over a 40 degrees F rise in temperature (if all 150 gallons in the tank rises by 40 F....which is unlikely without recirculation)
3. The amount of fuel that you added just before storage:
a. If you put a small amount of 50 F fuel into a "HOT" tank, nearly full of fuel, little expansion/contraction effect. And, fuel temperature equalizes very rapidly.
b. If you put a large amount of 50 F fuel into a "VERY HOT" tank with very little fuel in it, there is a bigger effect as the fuel expands and then the tank shrinks upon shutdown/cool down. And, tank material temperature equalizes much more slowly, in comparison to fuel.
4. The amount of fuel used getting to the storage "rest" condition:
a. In other words, how close was the fuel level to the cap seal when finally parked and leveled. If the sender gasket was weeping, that's a good sign that the fuel was right at the cap seal level.
When you put the coach away, the fuel and the tank were warm from the day and from the fuel recirculation. Hypothetically, if the tank was right at full (fuel at the cap seal) and the tank (on average) shrank .074 of an inch in length, width and height (as the tank cooled), that's 1.2 gallons less capacity in the tank, but the cooling of the fuel should have shrunk the fuel volume by 2.7 gallons,
if fuel (plus tank) all cooled down by 40 F.
So I would say that if the tank was "Chock a Block Full" and the coach was off level by just a fraction of an inch, the vented cap and a slightly "off level" coach is more likely the cause.
I know that I have to be very careful with mine due to that reason.
My cap is rubber o-ring sealed to the filler neck, but the cap has to breathe or the tank would be "vacuum collapsed" as the fuel is used (I have no other fuel tank vent that I am aware of..............just the Port and Starboard vented fill caps).
Since all tanks have to be vented to prevent collapse, for those that have unventilated caps and a tank vent instead, where is your vent? From where is it visible and to where does it drain??
The HWH leveling is not overly exact and can be quite different (+ or -) due to the system hysteresis. Thus, if fuel happens to be right at the cap when leveled and then even small atmospheric temperature or pressure changes occur, it will push fuel out the vented cap (small center hole in the white plastic fitting centered in the cap) whenever fuel expansion or tank contraction conditions happen to be just right.
Leveling AWAY from the leaking cap takes care of the problem, IF you don't flood the fill cap on the other side of the coach when you re-level the coach.
Long winded, I know.
Hope it adds some insight/puts your mind at ease,
Best wishes,
Neal
I'm Quoting Mikes Email, I think he has the solution. As soon as I can get down on my knees I'll check this out. Makes sense that the tank should be vented somehow. Thanks all for the help.
Gary B
Gary,
Well, I learn something every day! And that's good! Karma to Mike!
If I had ever noticed that vent hose, near the center of fuel tank before, I had forgotten about it over time.
I just crawled under, took the hose out of the "free-end" hold down clamp, rigged another hose to the end of it and easily blew air into and sucked air out of the fuel tank. So my hose is free to breath at will. I also just re-checked both of my vented tank fill caps. I can blow air through them as well as suck air through them, so they are free to breath at will, although pushing air through them requires overcoming some small resistance.
So I'm still of an opinion that if my tank is "Chock a Block Full" and the coach is off level by just a fraction of an inch, the vented cap and a slightly "off level" coach is more likely to cause your type of leak.
I also noticed that the filler neck seating surfaces both had some "gooey" buildup on them, which would likely prevent the gasket from sealing perfectly, so that also might have contributed to fuel seepage, whenever I've had fuel at that level during storage.
Neal
Neal,
Our fill caps have o-ring seals and non vented type, with only the vent in the top of the tank. We were always under the impression that the factory went this way so if you are not level filling you wouldn't leak fuel out the low side. This may not be the case for everyone and your coach may vary.
Pamela & Mike
I had mine leak under the screw in insert. Had to reseal that part just last month. On my old coach I had to yank it out and reinstall a new one.
Bill W, Was kind enough to send me a PDF of the typical fuel tank in our FT's. What I found interesting is that the clearance between the end of the pickup tubes and the tank bottom is clearly shown. In the past there has been discussion about running genny til out of fuel and how much fuel is left when this occurs. You engineer types probably have a formula that will tell how many gallons are left past end of genny pickup. And no, I DO NOT advocate running fuel down to genny cut off, just interested in that I can now see graphically where pickups are and length.
Gary B
Will crawl under mine to inspect vent as soon as I can, will have 40 staples removed from knee t'morrow, that will help mobility some.
Here is a picture of our U320 showing the location of the fittings on top of the tank.
There is a fuel vent on top and the hose runs down the front side of the bulkhead.
Gary, thanks for the PDF of the tank. I sure that is a scaled down version of our 195 gal tank.
IIRC, there were something like 5 different internal tank baffle revisions for our model year (2003). I'll try to remember to look for our copy and scan it in next time we're at the coach.
Michelle
Here is a copy of ours. After 10 years I finally found out that it has only 144 gallons of usable fuel. Don't ask how I know. ::)
I believe the vent has a safety feature built into it. In the even the coach were to tip on its side or upside down fuel would not run out. I've noticed new coaches have the exact same vent as my 21 year old coach.
Took coach out of storage and am now in FL. I finally got to look at fuel tank vent and could find nothing wrong, vent is open.
I suspect that I overfilled the tank and coach was setting slightly off level and fuel did not reach vent location on top of tank but did reach filler cap and that is why fuel leaked from cap area and not from vent.
I'll watch closer in the future how full I fill.
Gary B
Gary, after some time it seems that the epoxy they used to hold in the screw portion of the filler neck fails and allows fuel underneath and spills down the side. You might check that.