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Topic: At what point is a partially full fuel tank subject to algae growth? (Read 1841 times) previous topic - next topic

At what point is a partially full fuel tank subject to algae growth?

Rather than focusing on answers related to getting a maximum fill up of fuel, let me ask my question in a different way. 

But first, here is my concern.  We like to keep our tanks as full as possible to avoid the development of algae in the fuel.  We rarely sit for more than a few days with less than 3/4ths of a full tank.  We plan our travel days to try to fill the tank as close to possible to our destination. 

When we sit for a month or more we have been able to have the tank needle on full.

So, my questions should have been:

At what point is a partially full fuel tank at risk for algae growth.
George Stoltz.  Retired from full-time living in a great Foretravel and now are back to living in a traditional sticks and bricks in Florida.

Re: At what point is a partially full fuel tank subject to algae growth?

Reply #1 –
George,

Algae grows at the interface between diesel and water.  Water can get into your tank from a fueling source or from condensation in your tank.

Filling your tank with diesel minimizes condensation as a source of water. 

There is no magic formula for how full is full enough.  More is better.  When the dew point of any air in the tank is reached, that moisture condenses and goes to the bottom of the tank (water being heavier than diesel). 

The air (any gas) changes volume with change in temperature MUCH more than does a liquid (diesel).  So the more air you have, the more the tank "breaths" through the tank vent line.  Heating in the daytime  causes air to leave the tank and cooling at night causes air to go into the tank.  When that "new air" reaches the dew point, it also condenses.  Repeat each day/night.

My advice is to use a BIOCIDE  if you store your diesel over 2 months in the summer or 3 months in the winter.  And as you observe, full is better.

You can get a biocide at any marine store-- boats have the same diesel storage issues as we have.

Brett
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: At what point is a partially full fuel tank subject to algae growth?

Reply #2 –
George,
You worry a little too much.  Might come as a surprise! :-).
 
I park my coach in FL for six months every November - filled 3/4 fill or more.  Mom uses for 6 months. Aquahot, etc. I come down, starts right up, back to Chicago I go.
 
Leave it full when you park. Enjoy. Leave. Repeat.
 
Tim
Tim Fiedler    2025 LTV Unity MBL on Order
2000 Chevy Tracker 2 Door Convertible 4WD Now lifted 4.5"
1985 Citroen 2CV6 Charleston
Murphy Rebel on wheels with 175HP Titan
Cessna P337
1980 48' Westport MY (!/4 Share)

Re: At what point is a partially full fuel tank subject to algae growth?

Reply #3 –
Tim,
 
I think you are right.  I also suspect that some of the problems that beset owners of all motorhomes are those that owners  don't try to avert.  I think the way we are keeping our tank nearly full is a good plan.  We'll probably put some algaecide in our tanks for the 3 month stay in Florida in 2011.
George Stoltz.  Retired from full-time living in a great Foretravel and now are back to living in a traditional sticks and bricks in Florida.

Re: At what point is a partially full fuel tank subject to algae growth?

Reply #4 –
Hey George, the trick when you are in FLD in 2011 is to take a trip in the middle to maybe the Brooksvilles rally and FMCA or the RV super show and fill the tank again.....
2025 Wanderbox Outpost 32 on F600 Expedition Motorhome
2015 Born Free Royal Splendor on Ford 550 nonslide version  for sale
Former Coaches  covering. 360,000 miles
1999 34 U270
2000 36 U320
2001 42' double slide U320
2018 Jeep Rubicon

Re: At what point is a partially full fuel tank subject to algae growth?

Reply #5 –
Hi,

We live in the foothills of the Sierras in California with not a flat road to be seen.  Our diesel tank is kept at 1/4 tank or lower with the water/holding tanks empty or with a bit of water only and the propane tank with only enough for the trips we will be making. At roughly 7lbs/gal for diesel and 8.35gal for water, you can quickly see that the liquid on board can be a sizable percentage of your total weight. This translates into reduced fuel mileage, less performance on hills (especially at altitude) as well as increased braking distance in an emergency.

Brett has an excellent solution, use a biocide available at marine fuel docks anywhere. The marine environment is much more inviting for the growth of algae than anywhere else. The biocide will kill any growth in the tank and the filters will isolate any water from condensation. The primary filter should have a drain on the bottom to remove the water with a weekly check when you run your engine. Our fuel tanks are aluminum so rust is not an issue.

I have operated diesels of all types since 1970 and with the use of a biocide and regular filter service, have not had any problems. After pontificating on the above, if I lived on the flat, I would probably keep my main tank full.

Pierce & Gaylie Stewart
'93 U300/36
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: At what point is a partially full fuel tank subject to algae growth?

Reply #6 –
I have been a commercial fisherman on the North Coast of BC Canada for well over 57 years.
have used biocid with little success. The best expensive thing is a thing called Alge-X, the cheap thing if you have non magnetic fuel tank is several small do-nut magnets hung inside the fuel tank above the bottom. Alge-x is an aluminum housing containing a 3 inch magnet that the fuel must go through. They work fine if your engine has fuel return line that really returns any amount of fuel to the tank.
Harold Campbell harlynnboat@gmail.com
Harold Campbell
1992 U280 GV 36'

Re: At what point is a partially full fuel tank subject to algae growth?

Reply #7 –
I have wondered about this as George has. I bought my coach last April and aside from a trip to the DMV a couple of weeks later, it has mostly sat with the tank a little over 1/2 full while I've worked on refurbishing and repairing it. Prior to my taking possession, the coach had been mostly sitting for 2 1/2 years previously (pretty sure with less than a full tank).

It was taken in for chassis service two weeks ago (should be ready in a day or two). Among other things, the fuel tank had to be pulled to repair a few holes my helper managed to drill into it from the generator bay side (long story - he thought he was drilling into a bulkhead, until it started leaking.) I was concerned about algae growth, since it sat so long with only some fuel in the tank.

I spoke to the mechanic on Friday and he told me the tank was repaired and back in the coach. I asked about algae and was told that aside from a little dirt in the bottom of the tank, it was clean inside. Go figure.

I have read of similar instances with boaters. Months of partially filled tanks with no issues. I do not know why this occurs in some instances and not in others. However I do believe that I will begin using an additive just for peace of mind.

Steve
1991 U225 Grand Villa

Re: At what point is a partially full fuel tank subject to algae growth?

Reply #8 –
Let me add a little perspective to this one, having worked with diesel boats and RV's for decades.

Algae ONLY grows at a water/diesel interface.  Anything you can do to minimize the water in the tank helps.  This does NOT apply to gasoline, as gasoline, particularly with alcohol will absorb a reasonable amount of water and allow it to be burned.  NOT SO with diesel.  Diesel will absorb zero water.

So, best practices is to do everything you can to minimize water in your tank.  No water, no algae.  Keeping the tank full substantially reduces condensation and therefore water in the tank.

Here is an article I wrote for the FMCA Magazine:


Do you park your diesel coach with a full fuel tank?


First, let's look at what happens if you park your coach with 1/4 tank of fuel-- assume total capacity 100 gallons.

As you burned the 75 gallons of diesel, that space in the tanks was replaced with AMBIENT AIR. At whatever temperature AND HUMIDITY the outside air is at that time. So you now have 25 gallons of diesel and, particularly, if driving in a hot/humid area, 75 gallons of hot HUMID air.

OK temperature drops to the dew point OF THAT HUMID AIR IN THE TANK. It CONDENSES. And since water is heavier than diesel, it goes to the bottom of the tank where it can cause "algae" growth and/or rust the tank.

Each day, as the temperature rises, air and diesel in the tank EXPAND-- actually, air just goes OUT of the tank through the vent line. This happens even if the 75 gallons of air in the tank was dry and/or cold.

Each night, as the temperature falls, air is sucked into the tank through the breather line. As temperature continues to drop, the water vapor CONDENSES and goes to the bottom of the tank.

Repeat 30-100 times. NOT GOOD!!!!!

And yes, even if you are a desert area, your tank WILL get down to the dew point and there will be condensation.

If you fill the tank before parking, there is a MUCH smaller volume of air to condense.  Also, liquid (fuel) expands and contracts much less with temperature change than a gas (air) so there is far less "breathing" of the tank.

Add a biocide if storing fuel over 3 months.

And, if storing with fuel purchased in the summer or fall, use an anti-gel additive available at Walmart, etc.  If you fuel in the winter, the fuel already contains the anti-gel properties.

Brett
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: At what point is a partially full fuel tank subject to algae growth?

Reply #9 –
Fuel additives are always a good idea. I usually pop a quart in with every 150 gallons. Unless you get algae from an outside source, you won't grow any unless you have some water in the tank. It grows in the water/fuel interface. It also likes warm weather. It showed up a lot in early Lear jets where there was water in the fuel and it was exposed to the sun on the wings where the fuel tanks are. A nice warm, moist condition. Filters clogged on takeoff and...

Air always contains a certain amount of moisture. If the tank is partially full, there is some room for the air. In a marine environment, the air has a lot of moisture in it. When that air touches the cold wall of the tank, the air temperature drops in the boundary layer and the air cannot hold as much moisture in suspension so it condenses on the wall of the tank and it runs down into the bottom of the tank. With the right (warm) temperature, algae may (and only may) grow. Since the tanks in Foretravels have a pretty good cap, it is unlikely to exchange a great deal of air with the outside other than filling the empty space left as fuel is used. So, check your clear plastic primary filter cap and drain any water on the primary filter on a regular basis. Once you have algae in the tank, it can be difficult to get rid of. Keeping the tank full is a good way to minimize moisture. If you fuel from an above ground tank, make sure it has a filter before the nozzle and then double check your primary filter drain after running the engine for a few minutes or miles. Algae appears black in the filter or plastic drain. Have an extra set of filters on board. First sign of blockage is usually loss of power on hills. Gets worse as time goes by. May also have a rough idle for a few seconds until the fuel supply catches up with engine demand. You can cut the old filter open with a hack saw after changing to see if the culprit was algae. Remember, once you do have a tiny bit of algae, it WILL get worse. If you live or travel in a high humidity environment, check more frequently.

Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: At what point is a partially full fuel tank subject to algae growth?

Reply #10 –
I've gotten in the habit of occasionally putting a pickup tube from a small hand pump down into the low tilted corner of tanks on equipment and simply drawing out any water and crud the diesel is floating on.  It's pretty simple and to me seems pretty effective. 
"Not so  long ago we were a nation of risk takers, riding five million pounds of  thrust straight into space."  Joe Gresh
Chuck Pearson
1996 U295
2018 Can Am X3 TurboRS

Re: At what point is a partially full fuel tank subject to algae growth?

Reply #11 –
We periodically use a drill pump to suck a gallon from the bottom of our fuel tank, filling a glass gallon jar. We let the sealed jar sit still for a few days and observe if there are one or two layers indicating water or algae. We have always seen just good clear diesel and no layers.

Re: At what point is a partially full fuel tank subject to algae growth?

Reply #12 –
Quote from: Barry & Cindy –
We periodically use a drill pump to suck a gallon from the bottom of our fuel tank, filling a glass gallon jar. We let the sealed jar sit still for a few days and observe if there are one or two layers indicating water or algae. We have always seen just good clear diesel and no layers.

Typical for me also.  In addition, I have yet to ever remove any water by draining the water separator filter.  I'm starting to wonder if it's all a myth.
"Not so  long ago we were a nation of risk takers, riding five million pounds of  thrust straight into space."  Joe Gresh
Chuck Pearson
1996 U295
2018 Can Am X3 TurboRS

Re: At what point is a partially full fuel tank subject to algae growth?

Reply #13 –
Sure not a myth.  We have the clear-bowl Racor for our primary filter.  I do not open the drain unless I can see evidence of water or debris.  And, since all these engines are high bypass (for every gallon of diesel that goes to the engine, only a few ounces are burned-- the rest cools that area of the head and is returned to the fuel tank) checking the next time after you stop for fuel will tell you if you "picked up a problem".

To make that siphoning off the bottom of the tank, Foretravel's easy to access fuel tank makes that very easy.  To do it best, park/use jacks to make the fill neck where you will drop in the hose to siphon off the bottom the LOW part of the tank. Said another way, raise the opposite side/end with jacks, boards or parking on a slope, etc.  Water is heavier than diesel and will run down hill to that low corner.

On boats and RV's I use a 5' length of cheap clear plastic hose. Then wire tie the hose to a straightened metal coat hanger.  That way I can easily direct the suction end of the hose to the very deepest part of the lowest part of the tank.  Good $5 investment.

Brett
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: At what point is a partially full fuel tank subject to algae growth?

Reply #14 –
We use a bent/curved length of copper pipe to be sure we are on the bottom to suck up the bottom-most fluids.

Re: At what point is a partially full fuel tank subject to algae growth?

Reply #15 –
Quote from: Chuck Pearson –
Typical for me also.  In addition, I have yet to ever remove any water by draining the water separator filter.  I'm starting to wonder if it's all a myth.

It's just like buying insurance. You don't need it until you need it.  You will collect some nasty stuff, either next tank fill or ten years from now but sooner or later it will find it's way into your tank.

Does not take much extra time when checking your oil to glance at the belts and then shine a flashlight on the plastic fuel drain assembly.
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)