This was the subject of a recent post which is timely for lots of us up north and I thought it might be worth revisiting because of the lack of good info on the utility of filling your diesel tank before winter sets in. As you might infer, I am retired and have lots of free time to devote to some pretty esoteric subjects. This info comes from other sources and I'll be happy to provide references if anyone is interested: The maximum amount of liquid water in air at the following temperatures: 30C/86F 30 grams/cubic meter 20C/50F 17 grams/cubic meter 10C/13F 9 grams/cubic meter There are 28 grams per ounce, so 30 grams = 1.07 oz; 17 grams = 0.6428 oz. A cubic meter equals 264 gallons of liquid volume, therefore: A 200 gallon tank = 0.76 cubic meter. At 86F, an empty 200 gallon tank could contain 22.8 grams of water vapor, or 0.81 oz. At 50F, an empty 200 gallon tank could contain 12.92 grams of water vapor, or 0.46 oz. Note that this is the maximum amount of water vapor that a completely empty tank could contain, in neither case a full ounce of water. In order to condense water out of the atmosphere a surface must be much colder than the air. The problem for the condensation in tank theory is; how do we end up with a fuel tank that is much colder than the air? One way would be to have a very cold day that suddenly warms up dramatically, but when does this ever happen? The weather can turn cold very fast, but does not suddenly get very warm. Aluminum is second only to copper for rapid heat transfer properties; it will therefore adjust to atmospheric temperature changes quickly. Gasoline and diesel fuel, like water absorb heat and cold slowly. Thus one might expect to see sweating on the outside of a tank as the day warms up from cold mornings, but this doesn't occur. What's the point? It would appear that what you get after a winter of storing a full tank of diesel is a full tank of stale diesel If there are any other folks out there with too much free time like me who care to comment or poke holes in the theory, I'd be interested. Don
- Status
Here in Florida
Hey Don, what are the numbers for here in Florida when the temperature is 94 F with 100% humidity. You get instant condensation here when you pump fuel which has been stored underground and is 15 degrees cooler than the air inside the tank. I agree that the amount of condensation is not a big problem; I drain the water separator evry six months and perhaps get 2 ounces of water. Keep up the good work and stay busy.
Hey Don, what are the numbers for here in Florida when the temperature is 94 F with 100% humidity. You get instant condensation here when you pump fuel which has been stored underground and is 15 degrees cooler than the air inside the tank. I agree that the amount of condensation is not a big problem; I drain the water separator evry six months and perhaps get 2 ounces of water. Keep up the good work and stay busy.
This is Like Arguing about Vermouth in Martinis
There should only be as much as what sticks to the glass no more. They should also be stirred (slowly) not shaken. Shake a martini and you end up with a watered down martini. I was trained long ago to fill the bird up after each flight both in the Army and in the Air Force. Guess that stuff sticks. We need someone to put out two tanks one full one half full then check them in six months to see which has more water. Anybody really care enough about this issue to do that? I'd rather study the martini issue, sign me up. Franklin, the beer issue has no debate Shiner is the best beer this side of Bitburg.
There should only be as much as what sticks to the glass no more. They should also be stirred (slowly) not shaken. Shake a martini and you end up with a watered down martini. I was trained long ago to fill the bird up after each flight both in the Army and in the Air Force. Guess that stuff sticks. We need someone to put out two tanks one full one half full then check them in six months to see which has more water. Anybody really care enough about this issue to do that? I'd rather study the martini issue, sign me up. Franklin, the beer issue has no debate Shiner is the best beer this side of Bitburg.
Polyethelene Tanks?
Any diferences for polyethelene tanks? I never find any water in my water separator/fuel filter. I'm thinking of draining out the old fuel - just a couple gallons left at the end of the season anyway. Any problem with maybe leaving two gallons in the tank. or none?
Any diferences for polyethelene tanks? I never find any water in my water separator/fuel filter. I'm thinking of draining out the old fuel - just a couple gallons left at the end of the season anyway. Any problem with maybe leaving two gallons in the tank. or none?
My Concern is...
..that I don't want ANY water in my tank that can cause a problem. I have had a water separator on my boat for 10 years and have not found any water at all in that time. IMHO, for the small price of filling my 30 gallon poly tank (I add about 6 gallons), then it's worth it to fill it up at the end of the season. Why else would so many articles, books, etc. warn us about it? Besides, here in New England, we get temperature swings in the winter that would startle anybody.
..that I don't want ANY water in my tank that can cause a problem. I have had a water separator on my boat for 10 years and have not found any water at all in that time. IMHO, for the small price of filling my 30 gallon poly tank (I add about 6 gallons), then it's worth it to fill it up at the end of the season. Why else would so many articles, books, etc. warn us about it? Besides, here in New England, we get temperature swings in the winter that would startle anybody.
What about air that is cooled
Don: If the temperature of your 200 gal of tank goes from 85 deg (where the air could contain 0.81 oz of water) to 10 deg (where the air could contain about .25 oz. of water), where does the moisture into the air go? I can only deduce that it will precipitate or condense out and I will end up with about .56 oz. of liquid water (or ice) in my Diesel fuel. Do I want that .56 oz of water contaminating my Diesel? or can I prevent it by topping off my tank?.
Don: If the temperature of your 200 gal of tank goes from 85 deg (where the air could contain 0.81 oz of water) to 10 deg (where the air could contain about .25 oz. of water), where does the moisture into the air go? I can only deduce that it will precipitate or condense out and I will end up with about .56 oz. of liquid water (or ice) in my Diesel fuel. Do I want that .56 oz of water contaminating my Diesel? or can I prevent it by topping off my tank?.
A Little Hole poking ...
The computations miss the fact that it may not be a single volume of air condensing within the tank. Assume for a moment that water does condense out of the air in a gas tank. All tanks are vented in some manner, and I know for a fact that my tank is not air tight (no "swoosh" when you open it like a lot of cars). It is certainly possible for a volume of air which has already shed moisture to vent and be replaced with another body of wetter air which can again shed its moisture... and on and on. I'm not even gong to pretend I know the extent of the air exchange in the tank, but it has to happen to some extent. Also the idea of a cold surface condensing moisture from warm air happens all the time. Check the dew on your boat's deck on any given morning. That is simply the mechanics of the deck warming much slower than the surrounding air at sunrise. So if sun warmed air (which heats very quickly) were to get into a cold fuel tank (which heats very slowly, especially with many gallons of cold fuel in it to keep it cold), I see no reason why it would not result in condensation. I also agree that the amount of condensation may be minor, but for the $8 or so it costs to fill my tank at the end of the season, it's pretty cheap insurance, even if it dosen't matter. After all it IS fuel I would eventually buy anyway ( I never have had it go "stale"). When Spring rolls around I'm positive I won't be in the launch berth cranking the engine, hoping it will start before the batteries die while wondering if I made a mistake by not filling the fuel tank the previous Fall. There may be a dozen other things I did or didn't do that I'll question myself about, but not topping off the diesel tank won't be one of 'em. One less thing to keep me awake at night. Don, I also think you have way too much time on your hands. Paul
The computations miss the fact that it may not be a single volume of air condensing within the tank. Assume for a moment that water does condense out of the air in a gas tank. All tanks are vented in some manner, and I know for a fact that my tank is not air tight (no "swoosh" when you open it like a lot of cars). It is certainly possible for a volume of air which has already shed moisture to vent and be replaced with another body of wetter air which can again shed its moisture... and on and on. I'm not even gong to pretend I know the extent of the air exchange in the tank, but it has to happen to some extent. Also the idea of a cold surface condensing moisture from warm air happens all the time. Check the dew on your boat's deck on any given morning. That is simply the mechanics of the deck warming much slower than the surrounding air at sunrise. So if sun warmed air (which heats very quickly) were to get into a cold fuel tank (which heats very slowly, especially with many gallons of cold fuel in it to keep it cold), I see no reason why it would not result in condensation. I also agree that the amount of condensation may be minor, but for the $8 or so it costs to fill my tank at the end of the season, it's pretty cheap insurance, even if it dosen't matter. After all it IS fuel I would eventually buy anyway ( I never have had it go "stale"). When Spring rolls around I'm positive I won't be in the launch berth cranking the engine, hoping it will start before the batteries die while wondering if I made a mistake by not filling the fuel tank the previous Fall. There may be a dozen other things I did or didn't do that I'll question myself about, but not topping off the diesel tank won't be one of 'em. One less thing to keep me awake at night. Don, I also think you have way too much time on your hands. Paul
Morning Dew
Noone seems to have mentioned that this is a repetitive process. Now you have to add 1/4 to 1/2 ounce to your fuel for every day of storage that has a temperature swing overnight (ie most). This only assumes that whatever small amount of water that condenses goes into the fuel and that the air in the tank is replenished slowly with moist air from the vent. As a quick sanity check, think of the large amounts of dew regularly covering almost everything. That amount of water didn't come from the immediate boundary layer of air; rather the air keeps turning over and more water is 'squeezed' out. If air transfer in your tank were that fast and free, perhaps you would have water in your fuel on a regular basis. Just my $.02.
Noone seems to have mentioned that this is a repetitive process. Now you have to add 1/4 to 1/2 ounce to your fuel for every day of storage that has a temperature swing overnight (ie most). This only assumes that whatever small amount of water that condenses goes into the fuel and that the air in the tank is replenished slowly with moist air from the vent. As a quick sanity check, think of the large amounts of dew regularly covering almost everything. That amount of water didn't come from the immediate boundary layer of air; rather the air keeps turning over and more water is 'squeezed' out. If air transfer in your tank were that fast and free, perhaps you would have water in your fuel on a regular basis. Just my $.02.
Myth - No we BUY the water
Hi Don, Congrats for raising this one again. Some time back I did a similar calculation for my H376 tank. Worse case scenario:- Tank empty - volume 30 US Gals = 114 litres. Ambient air always 100% relative humidity. Day temperature 20°C = 68°F. Night temperature 5°C = 41°F. Assume air inside tank is always 100% R Humidity. Ignore barometric pressure changes as the day/night cycle does not occur as frequently and may actually reduce the day/night effect. Water contained in the empty tank at 20°C is 2 grammes = 2 ml = 0.12 cu inch of which 1.2 g will condense on the tank walls when cooled - a once off instance per fuel fill up. Now when tank temp drops to 5°C it 'breathes in' 6 litres of air = 0.2 cu ft or two human lungs full. Cooling this air to 5°C releases 0.062 grammes =0.062 ml of water = 0.004 cu in. Assume this happens 365 times a year. Total water released = 22.6 grammes = 22.6 ml = 1.4 cubic inches per year. But: We know the air is NOT always saturated, the tank not always empty, the day/night temperature rarely changes by 15°C = 27°F and the tank is located at water level so is mainly held at the water temperature by thermal conduction through the hull. So how does the water get in there? Answer - WE BUY IT FROM THE FILLING STATION - I don't believe in fairies! On my 376 I have had water problems on two occasions in the last ten years. On both occasions I drew off all the diesel and it contained between half and one gallon of water. ie. enough to reach the pickup tube. On each occasion I had refuelled from a supplier which had its tanks in the water. Once from a fuelling barge and the other from a marina. Tanks rot at the bottom so, diesel being lighter than water, the water enters rather than the diesel leaking out. IMHO that's how. A pal was manager of all filling stations (road) for the UK's largest fuel supplier. I asked him why don't trucks get the same problem? He replied "They do. There is a standing instruction to clean out their tanks every three months. A good gas station might do it once in two years. A bad one - never. Another standing instruction is not to sell any diesel for 3 hours after filling their tanks. Nobody bothers about this".
Hi Don, Congrats for raising this one again. Some time back I did a similar calculation for my H376 tank. Worse case scenario:- Tank empty - volume 30 US Gals = 114 litres. Ambient air always 100% relative humidity. Day temperature 20°C = 68°F. Night temperature 5°C = 41°F. Assume air inside tank is always 100% R Humidity. Ignore barometric pressure changes as the day/night cycle does not occur as frequently and may actually reduce the day/night effect. Water contained in the empty tank at 20°C is 2 grammes = 2 ml = 0.12 cu inch of which 1.2 g will condense on the tank walls when cooled - a once off instance per fuel fill up. Now when tank temp drops to 5°C it 'breathes in' 6 litres of air = 0.2 cu ft or two human lungs full. Cooling this air to 5°C releases 0.062 grammes =0.062 ml of water = 0.004 cu in. Assume this happens 365 times a year. Total water released = 22.6 grammes = 22.6 ml = 1.4 cubic inches per year. But: We know the air is NOT always saturated, the tank not always empty, the day/night temperature rarely changes by 15°C = 27°F and the tank is located at water level so is mainly held at the water temperature by thermal conduction through the hull. So how does the water get in there? Answer - WE BUY IT FROM THE FILLING STATION - I don't believe in fairies! On my 376 I have had water problems on two occasions in the last ten years. On both occasions I drew off all the diesel and it contained between half and one gallon of water. ie. enough to reach the pickup tube. On each occasion I had refuelled from a supplier which had its tanks in the water. Once from a fuelling barge and the other from a marina. Tanks rot at the bottom so, diesel being lighter than water, the water enters rather than the diesel leaking out. IMHO that's how. A pal was manager of all filling stations (road) for the UK's largest fuel supplier. I asked him why don't trucks get the same problem? He replied "They do. There is a standing instruction to clean out their tanks every three months. A good gas station might do it once in two years. A bad one - never. Another standing instruction is not to sell any diesel for 3 hours after filling their tanks. Nobody bothers about this".
thanks for the great comments
Consensus seems to be old school- new school thinking similar to the old adage about not storing batteries on concrete. Since there is virtually no repetitive breathing process in a one vent tank, water can only come from three sources: 1. you buy it as Donalex says (exacerbated by buying it in the fall), 2. condensation localized to the vent or fill tubes, or 3. condensation inside the tank for #2 aND 3, , the only places in the US subject to sufficient and constant temp swings between day/night acording to NWS statistics are located in the southern portion of the U.S. during winter. I guess it's impossible to prove the theory without sufficient practical testing. Diesel is essentially high volatility components evidenced by the odor given off even at extremely low temp so the real question becomes whether it's preferable to have a little water or a large amount of volatilized ("stale") fuel for which there is clear evidence that diesel ages poorly. The issue then becomes whether it's easier (and cheaper)to remove a few oz of water or old fuel. I realllllly need to get a winter hobby...
Consensus seems to be old school- new school thinking similar to the old adage about not storing batteries on concrete. Since there is virtually no repetitive breathing process in a one vent tank, water can only come from three sources: 1. you buy it as Donalex says (exacerbated by buying it in the fall), 2. condensation localized to the vent or fill tubes, or 3. condensation inside the tank for #2 aND 3, , the only places in the US subject to sufficient and constant temp swings between day/night acording to NWS statistics are located in the southern portion of the U.S. during winter. I guess it's impossible to prove the theory without sufficient practical testing. Diesel is essentially high volatility components evidenced by the odor given off even at extremely low temp so the real question becomes whether it's preferable to have a little water or a large amount of volatilized ("stale") fuel for which there is clear evidence that diesel ages poorly. The issue then becomes whether it's easier (and cheaper)to remove a few oz of water or old fuel. I realllllly need to get a winter hobby...
I store
my batteries on a wet concrete floor. I also drain the diesel out of my tank each winter and fill the tank with water in order to avoid worrying about how much water has condensed into the tank. I know exactly how much is in there....
my batteries on a wet concrete floor. I also drain the diesel out of my tank each winter and fill the tank with water in order to avoid worrying about how much water has condensed into the tank. I know exactly how much is in there....
I've filled my tank each fall for the winter
And my fuel has been spotless and clean as a whistle for the last 6 years in this boat. I used to do the same for 8 years on my old boat. Never had a "bug" algee or cloudy problem. (I did run out of fuel once
) I usually put some sort of deisel additive in but not always. In fact I haven't even changed out my racor filter yet on my new (6 years old - almost 600 hours now) boat. (knock....knock....knock.....don't want to jinx myself now) I have a vacuum guage on the racor and it still barely moves so I feel really confident that the filter is not getting 'clogged'. Maybe its just that I always get good deisel from the sources I buy from The only time I ever saw water in my racor bowl was one time I think I forgot to tighten down the deck fill cap and it rained hard one week. The only real downside I see to filling the tank each winter is that when you fill it all the way up in the cold temperatures you stand a very good chance of "vent" overflow in the spring when you get one of those really warm days. I guess deisel expands quite a bit.
And my fuel has been spotless and clean as a whistle for the last 6 years in this boat. I used to do the same for 8 years on my old boat. Never had a "bug" algee or cloudy problem. (I did run out of fuel once
) I usually put some sort of deisel additive in but not always. In fact I haven't even changed out my racor filter yet on my new (6 years old - almost 600 hours now) boat. (knock....knock....knock.....don't want to jinx myself now) I have a vacuum guage on the racor and it still barely moves so I feel really confident that the filter is not getting 'clogged'. Maybe its just that I always get good deisel from the sources I buy from The only time I ever saw water in my racor bowl was one time I think I forgot to tighten down the deck fill cap and it rained hard one week. The only real downside I see to filling the tank each winter is that when you fill it all the way up in the cold temperatures you stand a very good chance of "vent" overflow in the spring when you get one of those really warm days. I guess deisel expands quite a bit.- Status