full tank vs. empty tank for storage

[dingbat]

Re: full tank vs. empty tank for storage

Are you seriously citing Pascoe as a "well-respected" surveyor?? By whom? Some of his stuff is OK, some is atrocious. Thermodynamics is DEFINITELY not his strong suit.

You really doubt tank condensation? Have you ever had a basic thermodynamics class? Can you solve problem 8.171? I'll do it at lunch, don't have time right now and it's been a while since I've had to do any tank calcs - have to dig up a psychrometric chart.

You are ignoring the fact that there is both condensation and evaporation at work here. There is no doubt about condensation. There is also no doubt about evaporation. The argument is whether or not the evaporation and condensation cycles reach dynamic equilibrium or not.

 

[H20Rat]

Re: full tank vs. empty tank for storage

You really doubt tank condensation? Have you ever had a basic thermodynamics class? Can you solve problem 8.171? I'll do it at lunch, don't have time right now and it's been a while since I've had to do any tank calcs - have to dig up a psychrometric chart.

...

We build tanks for the aerospace industry, and there's a reason EVERYTHING built is purged and stored with dry nitrogen inside.

So I'm assuming those purged tanks are stored with an open atmospheric vent on them?

You ignored a slight problem... Boat tanks are far from sealed, they have a nice little atmospheric vent on them, and through thermodynamics, the air inside the tank is going to seek equilibrium with the air outside. (problem 8.171 that you mentioned above had the word 'contained'. It isn't a boat gas tank, as vapor/air is not contained in any sense.)

 

[WIMUSKY]

Re: full tank vs. empty tank for storage

Facts? and figures aside, here's what worked for me over the years. I leave no more than 1/2 a tank over winter. I use the proper amount of seafoam to stabilize the fuel. In the spring I top off the tank with fresh fuel. We're having the same conversation on a GTO forum. I do the same procedure with my GTO. I live in the northwoods where the air is dry as a bone in winter....

 

[lkbum]

Re: full tank vs. empty tank for storage

From the Mercury Marine website - http://www.mercurymarine.com/service-and-support/storage-and-maintenance/faqs/mercruiser/?category=winterization#EthanolStorage
"What should be done when storing boats with ethanol-blended fuels for extended periods?
Follow the instructions for normal storage preparation found in the Operation, Maintenance & Warranty manual. When preparing to store a boat for extended periods of two months or more, it is best to completely remove all fuel from the tank. If it is difficult or not possible to remove the fuel, maintaining a full tank of fuel with a fuel stabilizer added to provide fuel stability and corrosion protection is recommended. It is best to add the stabilizer and fuel treatment to the tank at the recommended dosage, run the engine for 10 minutes to allow the system to be cleaned, shut off the fuel valve to interrupt the fuel supply and allow the engine to run until it stops, and top off the tank until it?s full to reduce the amount of exchange with the air that might bring in condensation. Do not cap the tank vent and do not fill with fuel to the point of overflowing. Some extra space should be maintained in the tank to allow for expansion and contraction of the fuel with temperature changes. A partially full tank is not recommended because the void space above the fuel allows air movement that can bring in water through condensation as the air temperature moves up and down. This condensation could potentially become a problem.

Mercury Marine Fuel System Treatment & Stabilizer can help maintain fuel systems in storage. It contains oxidation inhibitors to reduce oxidation and gum formation, metal-chelating agents to protect metal components from corrosion, water-absorbing agents to reduce the presence of free water, and dispersants to help suspend and disperse debris. When placing the boat back in service, be sure to reopen the fuel valve to the engine.

 

[bruceb58]

Re: full tank vs. empty tank for storage

I leave it with whatever it had the last time I used it!

I am actually more concerned with a large amount of fuel going stale than condensation since I live in SoCal so if I had a preference, it would be more toward empty.

 

[Philster]

Re: full tank vs. empty tank for storage

So either way is fine -- haha -- as said early on.

I store mine 9/10 full because, although leaving it empty is best, I can't do that most times. I can't plan to run 'er out of fuel or even close. I tend to keep the tank topped off, because I never know when/how I am going to use the boat. Always head out with a full tank, especially in an ocean environment.

She sits with fuel, so I top it off for winter layup... I add fuel treatment, too. It sits from about October 15 to April 15.

.

 

[45Auto]

Re: full tank vs. empty tank for storage

Philster, you have to be the easiest guy to take the bait.

The point of my post was that you can't just jump into a thread an operate off a flawed premise.

So why did you?

It was instructional in how to make a case, cite a reference, etc.

LMAO!!! Here, I'll correct that statement for you:

"It was instructional in how NOT to make a case, cite a reference, etc."

Your cite is nothing more than more anecdotes

And yours is considered what???

What we could do is find a study that shows just what happens inside a tank... or did that happen already?

It's happened many times on aircraft where it matters. On a boat it's irrelevent, worse thing that happens is you get towed back in.

Civil Aviation Operations Advisory on Aircraft Ground Handling and Servicing:

"There is no way of preventing the accumulation of water formed through condensation in fuel tanks. The accumaulation is certain and the rate will vary"

Exxon Aviation Fueling:

"Bulk quantities of moisture ... may be caused by .... condensation of moisture from the atmosphere"

Shell Winterizing Your Aircraft:

"This condensation is inevitable if air is present in the tank and will in turn lead to the build up of water in the bottom of the tank."

Don't have pics of the one below yet, the ones above were from the last discussion on this a month or so ago.

FAA Power Loss Advisory, page 3:

http://rgl.faa.gov/REGULATORY_AND_G...7a95930fa862569d10077bd60/$FILE/ac20-105b.pdf

(1) Water contamination continues to be a major cause of fuel related accidents. There are three ways water can enter a fuel system. The first is condensation, or the reduction process in which the moisture in warm air is reduced into liquid water. This phenomenon is exactly what causes windows in a warm house to ?sweat? during the winter months. In an aircraft, condensation can happen inside a less than full fuel tank. When a temperature difference occurs between the walls of the fuel tank and the air in the tank, water droplets will form on the inside top part of the fuel tank walls and drain down into the fuel. The effects of condensation can be reduced by keeping the fuel tanks full while the aircraft is parked.

Wright-Patterson study on integral fuel tank corrosion:

http://www.corrdefense.org/Academia...- LEARD - IFT_Corrosion_Leard_TriService2.pdf

Thorough wing tank sumping practices remove much of the present water, but will not remove the moisture content soluble in fuel. Condensation due to ambient and operational temperature fluctuations will condense this moisture as well as ambient moisture inside IFTs. (IFT's are Integral Fuel Tanks)

You put your carb and points back on your boat yet?

 

[Philster]

Re: full tank vs. empty tank for storage

45Auto, you've completely ignored the other points/links, especially one from Mercruiser.

Should we now cite iboat references wherein you tell people to observe what the manufacturer recommends?

And you can quote me all you want.

I did cite a reference (and see someone else cited Merc as one after me. Kudos to us both)

I did not work off a flawed premise (hence the reference).

My reference is not an anecdote because it was not just some story or statement, it was based on a test and measurements.

These games where you quote everything to death and then make false statements are hurting your arguments.

You posted some good information. So did I and so did ikbum.

Just curious about aviation fuel: When those aeroplane tanks are sitting full, what's the ethanol doing over the long haul as they sit for 6 - 18 months?

 

[Philster]

Re: full tank vs. empty tank for storage

Deleted bad link.

 

[45Auto]

Re: full tank vs. empty tank for storage

45Auto, you've completely ignored the other points/links, especially one from Mercruiser.

I haven't ignored anything. I'm not even going to try to discuss phase separation on here. The only foolishness I was addressing is this statement:

Is an empty tank prone to collecting condensation... or isn't it? I posit that it is not

I did cite a reference

Yeah, Santa Claus would have been as applicable ....

I did not work off a flawed premise

That's your opinion. Repeatedly stating it doesn't make it true. The FAA, thermodynamics, and reality all disagree with you. Do you also doubt that condensation occurs in engine blocks and exhaust systems?

Just curious about aviation fuel: When those aeroplane tanks are sitting full, what's the ethanol doing over the long haul as they sit for 6 - 18 months?

I don't know anybody that uses it in an airplane. Not worth risking your life. No such thing as "TOWAIRPLANE U.S.".

Though research is underway to advance the use of ethanol in aircraft, its use is forbidden as set forth in this U.S. Federal Aviation Agency 2006 Airworthiness Bulletin . The FAA expressly forbids the use of any ethanol containing fuel.

The Hawaii New Fuel Consumers site refers to a number of FAA documents, including documents that CANCEL previous authorization for certain aircraft to use gasoline from automotive service stations. It?s important reading for all who have the good fortune to be aircraft owners.

The only American aircraft allowed to use any ethanol bearing fuel are experimental aircraft licensed for such use. Otherwise ETHANOL USE IN U.S. AIRCRAFT IS FORBIDDEN!

 

[Philster]

Re: full tank vs. empty tank for storage

The ethanol in aviation fuel comment was (what I thought to be) obvious sarcasm.

Mercruiser and the aviation fuel suppliers differ in opinion because they are addressing different products (ethanol blends vs non-ethanol blends).

Santa Claus can bring you some non-ethanol treated fuel for Christmas.

If condensation is a serious issue, which must be addressed by keeping tanks full, that means that for the hundreds of days per year in which it is boating season, you had better keep the tank full at all times. Seems to be there's hundreds of overnight opportunities for condensation to form. Wouldn't just be a winter layup thing.

 

[AllAboard]

Re: full tank vs. empty tank for storage

They keep it full so when the weather gives us a break, they can get out without any interference slowing them down .

I leave the gas and treat it for the winter then come next season before I start it up I empty the tank (only 20 gallons anyway) and use it for my lawn toys for the summer.

....or they keep it full to keep from having to line the inside of their tanks with KREEM (yuk!), POR-15, or some other similar liner. Motorcycles are a good example because they too, are seasonal machines (depending on where you live) and look on any bike forum and you will see threads on how to fix a rusty gas tank. Hell, some get so bad they rust through....

I treat mine and keep it full until spring and uhhhhhhhhhh...; fire it up and ride it with the same treated gas. Never have any issues. I always did this on my 3-wheelers & quad too. Seems like some arguments either way. I just know I've seen ALOT of bikes & ATVs with tanks rusted so bad they had to be replaced.

... and again, what causes tanks to rust if it isn't condensation?

 

[Mark42]

Re: full tank vs. empty tank for storage

I store my two boats with the tanks as empty as I can siphon them. Both are plastic tanks, so rust is not an issue. Never had any water show up after the long damp winter.

I vote for empty tank storage.

 

[rbh]

Re: full tank vs. empty tank for storage

So that is a bunch of votes for full and a bunch of votes for empty.
So I guess either, or.
just don't sit in the middle for this vote.

 

[bruceb58]

Re: full tank vs. empty tank for storage

For most of us, I really don't think its that big of a deal. Probably most of the water that ends up in our tanks is going to be from being delivered that way.

Bottom line...use a water seperating filter and treat your gas with Sta-bil and or something that has a gas drier in it(contains IPA).

 

[45Auto]

Re: full tank vs. empty tank for storage

Santa Claus can bring you some non-ethanol treated fuel for Christmas.

Don't need it. We boat year round here!

Have you ever paid any attention to your Santa Claus Pascoe's "Fuel Condensation" crap, or do you just believe everything you read on the internet? Ever tried thinking for yourself?

Here's a couple of hints about a few of the more glaring errors. I may give you the answers later if I feel generous:

1) Figure out the relative humidity he's using for his amount of water in the fuel numbers. One of them is IMPOSSIBLE in this universe - you can't do it.

2) He states that a surface must be "much colder than the air" for water to condense out. If you know the temperature he's using (86F) and you've calculated the relative humidity he's using to get the .81 oz per tank, you can calculate what the "much colder" temperature must be that's required for condensation. Ever wonder why he doesn't give a number? It's obviously because he doesn't know it, if he did he would know how ridiculous his statements are.

3) He claims that aluminum is second only to copper for heat transfer properties - look up some common Tc (Thermal conductivity) properties real quick to see how much he knows about this.

4) He says that in 35 years of inspecting he's "rarely" seen tanks sweating. Is rarely 1 in 10? 1 in 50? Then in the next sentence he tries to cover his arse by saying "Note: Sweating may be likely to occur with boats in very cold waters when warm days are encountered." So do they sweat or not? Is it "rare" or "likely to occur"? What's his definition of "very cold waters" (again, he doesn't know enough to figure it out)? If it's similar to "much colder", then we're talking about just over one degree of temperature change ....

He was raked over pretty good four or five years ago on THT, the Boat Design forums, and about everywhere else when he first posted his junk.

Here's a few links that'll make it easy:

Psychrometric diagram if you want to do it manually:

http://www.uigi.com/UIGI_IP.PDF

Here's a nice internet psychrometric calculator if you don't want to do it manually:

http://www.sugartech.co.za/psychro/index.php

And here's an air density calculator so you can figure out the relative humidity he's using:

http://www.denysschen.com/catalogue/density.asp

 

[DaNinja]

Re: full tank vs. empty tank for storage

In aviation, we were chastised for not filling an aircraft before parking/hangering them. It was part for condensation and part because it's annoying to get an aircraft that has to be run to refuel before a flight.

I stored the Starcraft last year with a full tank of Stabil treated gas. I still learned the hard way that I need to be ready to change fuel filter/water separators when I stalled out about an hour in with 12 pax onboard.

I blame the 55 gallons of ethanol gas in a vented tank for eight months. This year I'm using Seafoam, as well, and plan to put her away with a full tank of NON-Ethanol gas. No ethanol if my boats/vehicles when I have an option.

 

[Philster]

Re: full tank vs. empty tank for storage

Don't need it. We boat year round here!

Have you ever paid any attention to your Santa Claus Pascoe's "Fuel Condensation" crap, or do you just believe everything you read on the internet? Ever tried thinking for yourself?

Here's a couple of hints about a few of the more glaring errors. I may give you the answers later if I feel generous:

1) Figure out the relative humidity he's using for his amount of water in the fuel numbers. One of them is IMPOSSIBLE in this universe - you can't do it.

2) He states that a surface must be "much colder than the air" for water to condense out. If you know the temperature he's using (86F) and you've calculated the relative humidity he's using to get the .81 oz per tank, you can calculate what the "much colder" temperature must be that's required for condensation. Ever wonder why he doesn't give a number? It's obviously because he doesn't know it, if he did he would know how ridiculous his statements are.

3) He claims that aluminum is second only to copper for heat transfer properties - look up some common Tc (Thermal conductivity) properties real quick to see how much he knows about this.

4) He says that in 35 years of inspecting he's "rarely" seen tanks sweating. Is rarely 1 in 10? 1 in 50? Then in the next sentence he tries to cover his arse by saying "Note: Sweating may be likely to occur with boats in very cold waters when warm days are encountered." So do they sweat or not? Is it "rare" or "likely to occur"? What's his definition of "very cold waters" (again, he doesn't know enough to figure it out)? If it's similar to "much colder", then we're talking about just over one degree of temperature change ....

He was raked over pretty good four or five years ago on THT, the Boat Design forums, and about everywhere else when he first posted his junk.

Here's a few links that'll make it easy:

Psychrometric diagram if you want to do it manually:

http://www.uigi.com/UIGI_IP.PDF

Here's a nice internet psychrometric calculator if you don't want to do it manually:

http://www.sugartech.co.za/psychro/index.php

And here's an air density calculator so you can figure out the relative humidity he's using:

http://www.denysschen.com/catalogue/density.asp

I'll concede.

Your efforts to cite proper references, which go beyond the presentation of mere anecdotal evidence, and invoking actual science into the discussion have done much to promote your argument. Further, you've convincingly debunked the 'condensation is a myth' argument that was presented earlier.

I think there is room left to polish up the soft skills, but the sarcasm (e.g., invoking Santa Claus and his good name into this) is actually enjoyable to me.

I appreciate the tenacity. Just don't mess with Santa.

 

[Mark42]

Re: full tank vs. empty tank for storage

I understand that not everyone can store their boats with the tanks empty. But if possible, I think it is better than storing with the tanks full for the following reasons:

- Siphoning the tanks empty makes it easy to test for the presence of water in the spring, from condensation or leaks. Inserting a siphon tube with the "water test" paste smeared on the end will indicate if water is present. If present, add a gallon or so of denatured alcohol to help absorb the water, then it can be siphoned out. (some times its hard to siphon the tank 100% empty, so adding some alcohol to absorb the water will make it easier to siphon out as much as possible). The "water test" paste is sold in the home centers for testing home oil tanks for the presence of water. It is smeared on the tank dip stick and changes color when water is present.

- Gasoline that is 3-6 months old, even with stabilizers added, is not as good as fresh gas. Stabilizers prevent the formation of sludge and reduce separation of components. The stabilizers do not replace the loss of the light petroleum products added to make starting easier. There are many different additives in gas, and Butane is one of them. It just flashes off, and because of the vent, it is lost, and you can not replace Butane in the gas. Typically the detergent additives that clean the engine are lost too. Old gas is just not as good as fresh gas. According to the major oil companies, gas can be stored for a minimum of 3 months with no major degradation when stored in a SEALED container that is full (with room for expansion). The key is the container being sealed, so that once the air space is saturated with petroleum vapors, it can not absorb any more, the the additives stay in the fuel. After about 3 months, many of the additives start to break down and lose their effectiveness.

- A tank that is empty can not leak dozens of gallons of gas into the boat if a leak does develop.

- Phase separation and buildup on the sides of the tank that can later peel and clog pickup screens just can't happen if the tank is empty.

- Right now, my boat uses pre-mix gas. Although there is 50:1 oil in the gas, I still siphon off all the gas into portable tanks and use it in the garden tractor, snow thrower, ATV, etc. I generally mix the pre-mix gas with an equal amount of regular gas when available, but running the pre-mix straight has not caused any problems in the small engine machines.
Even after doing this for 6 or more years. I've even used it in the old Merc Mountianeer with no issues.

- The boats permanent tanks are the white poly roto-molded tanks, and are small compared to other boats being 14 and 17 gallons each. Still, I have not experienced condensation in either tank, and they are stored empty. Because they are the white plastic, its easy to see if there is any liquid inside the tank just by looking at the side of the tank.

So, those are my reasons for storing tanks empty. If you choose to store your boat with empty tanks, I hope you have as good experience doing it as I have.

Regards,

Mark

 

[Ike-110722]

Re: full tank vs. empty tank for storage

All this talk about condensation aside for a moment, I want to address the "rust" issue.

First off, there are very few, by comparison with the entire boat population, Steel tanks, or iron, or anything else that rusts. Just to toss some numbers around, there are about 20,000,000 recreational boats in the US, about half of which are powered. The rest are canoes, kayaks sailboats and such. See http://www.uscgboating.org/assets/1/workflow_staging/Publications/394.PDF
The USCG reports only registered boats which is a little over 12 million. The National Marine Manufacturers Association reports about 20 million, The difference is in boats that are not required to be registered. In many states unpowered boats are not required to be registered, but these are not important to this discussion

Most powered boats in the US do not have steel or ferrous tanks. about half have roto molded polyethylene tanks, PE, plastic if you please, and they do not corrode. The rest have aluminum tanks. Aluminum does corrode, but only under certain circumstances. If left alone, dry, and unpainted aluminum has a natural oxide coating on it that prevents corrosion. Where the problem lies with aluminum tanks is either water is allowed to pool on the top, or collect on the bottom and this dissolves the oxide allowing the aluminum to corrode. You can recognize this immediatly because it looks like a white powder.

Water is not what causes the aluminum to corrode form the inside though. And most of the cases of aluminum tanks corroding form the inside have been due to phase separation of the fuel, that is the alcohol and gas separating into two layers. Yes this attracts water. But what really causes the corrosion are acids that form at the boundary between the alcohol and the gas. These eat the tank from the inside out causing pinholes, and resulting in your 20 gallons of gas ending up in the bilge.

Painting aluminum is not the solution because to paint alluminum it has to go through an etching process to remove the oxide and any contaminants. Paint will not stick for very long to aluminum that is not prepared correctly. Any slight imperfection in the paint, a nick, a scratch, a ding, exposes the unprotected aluminum resulting in corrosion at that spot.

This argument about condensation has been going on for about 50 years and for the most part everyone ignores the scientific evidence and makes their own conclusions. The US EPA has based much of their regulations on evaporative emissions from fuel tanks on the science of diurnal cycles of heating, cooling, condensation, and so on. Any one with a computer and internet access can look it up. That is why auto tanks are required to be sealed systems. This cannot be allowed on boats because a pressurized fuel system in a boat is a significant safety hazard, so boat fuel systems must be open to stay at normal atmospheric pressure. Some of this will become moot if the EPA requires vapor absorbing filters on fuel vent systems, but that is still in the proposal stage and the industry is still trying to figure oiut how to do it and still leave the vent open to the atmosphere.

Now, there are some steel tanks on boats, mostly steel hulled boats and almost entirely diesel, and we all know that steel rusts. (I am not including stainless steel because there are very few boats with SS and it is a special case) There are at the last guestimate about 100,000 diesel powered boats in the US. (the USCG does not break it down by type of fuel) As far as I have been able to determine there are no firm figures on how many of those are steel. But a good guess would be 10 -20 thousand. Virtually all of those are painted. Like aluminum this involves a process to be done correctly. But if done correctly steel tanks will last as long as aluminum or any other metal. ALcohol does not affect these tanks, but, unless the EPA gets it's way, none have ethanol in the fuel.

There are some boats, virtually all diesel, that have fiberglass tanks. But there are a few gas boats as well. Their problems with ethanol have been well documented by BoatUS and others. Do not use gas with fiberglass tanks.

For more on aluminum tanks see Much Ado About Ethanol http://www.uscgboating.org/assets/1/workflow_staging/Publications/394.PDF

and Aluminum Tanks on Boats; To Paint Or Not to Paint. http://newboatbuilders.com/docs/aluminum.pdf