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  #11  
Old 06-22-2008
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Also, once a certain amount of water was in the tank, the partial pressure of the water evaporating would prevent more water from entering the tank and condensing out.
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  #12  
Old 06-22-2008
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Quote:
Originally Posted by halekai36 View Post
FWIW I drain my tank in the winter and plug the vent to prevent any air turn over. I also remove my wet exhaust hose and plug the exhaust and air intake.. Overkill? Maybe but I have yet to ever rebuild or even repair the internals, fuel injection pump or injectors of a diesel engine so I think I'll keep doing it..
Draining the tank for the winter is an excellent idea, but I'd suggest leaving a small amount of fuel around (just the dregs) and cleaning this out with a rag before you refill. Fuel vapour will minimise the chance of rust forming and contain any condensed water.

As for plugging the vent: So long as you remember to unplug it when you refill the tank, you'll be fine, but I wouldn't suggest this if you've still got fuel in the system and you're likely to have extremes of temperature. I have a few photos here someplace of a large storage tank that collapsed because of a cold snap whilst the vents plugged for maintenance (painting) - highly embarassing for the owners!
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  #13  
Old 06-22-2008
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Mr. Pascoe spent a great deal of effort to get it exactly wrong.

The first fundamental error he made was in associating fuel tank temperature with air temperature. Fuel tank temperature is much more likely to be associated with sea water temperature than ambient conditions. the air in the tank though is much more likely to be closer to ambient temperature and so will go through a warming and cooling phase each day.

This can easily be observed in the bone dry cargo tanks of a tanker. Dry the night before and an inch of water on the double bottoms in the morning. Condensation.

It is not entrained water that produces water during combustion. Water is a natural by-product of combustion. Those of you with 80-90% efficient furnaces know this because your furnace has a combustion chamber drain on it! That's the one that is usually PVC and goes to a little pump in a box which pumps it to your drain line or, alternatively it goes to your floor drain.

All fuels expand and contract with temperature change. If you take bunkers in Maine and press your tanks up, and then sail to Florida without using any fuel you can expect to see fuel coming out your tank vent.

Refineries routinely strip water out of their fuel oil tanks. It is not regarded as a desirable aid to combustion in their view. Likewise motorists are cautioned to avoid service stations with a history of water in their fuel tanks. There is technology for injecting water during the combustion process to provide cleaner burning of less refined products but the water is injected at the burner tip and is not carried in the fuel tanks. Water in the fuel tanks of any combustion type power plant is undesirable. Steam turbine engines, specifically oil-fired boilers, have fuel water separators that the yachtsman would envy. Slugs of water have a nasty habit of first extinguishing the flame at the burner tip and then, when fuel returns, the combustion process is reignited by the heat off the brick-works of the boiler in an uncontrolled fashion generally resulting in catastrophic failure of the firebox. The USS John F. Kennedy got an unexpected three month shipyard visit from ignoring such matters.

And yes, if you were to place an empty tank in 60F water, half submerged, with an ambient daytime temperature of 80F, and vented it, you might be quite surprised at the amount of water that would magically appear in it's bottom. Filling it half full with fuel oil, of any type, would not significantly alter the results.

Lastly, the data cited on rusting within internal combustion engines due to condensation is poppycock, particularly for engines in a marine (read humid) environment. Diesel lifeboat motors have block heaters that are left plugged in year 'round regardless of temperature. Aside from keeping the lubricating oil warm in cold climes they reduce condensation, particularly in the tropics. and one of the prime reasons that biocides are used within diesel storage tanks that do not get drained and refilled routinely is that the condensed water vapour is a major ingredient to the algae that grows in diesel fuel.

There might have been something in Mr. Pascoe's conclusions that was correct but, if there was, I've either overlooked it or it's nonexistent.
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Actually, if condensation did not occur, there would probably be no need for a biocide additive to diesel fuels, as the algae that grows in the tanks only grows along the diesel and water interface. No water--->no algae.
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Old 06-22-2008
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I have known David Pascoe for years and admire his expertise on many things, but this is something we disagree on. Sailaway's analysis is right on. Sailingdogs comment about biocides is too.

Condensation does occur in tanks, especially metal tanks when there are extreme temperature swings.
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Its not the case that it condensation doesn't occur, its just that it is to little to be concerned about. Also the tank is not filled with air, it is air and fuel vapors.

By the way for all the water to condense out of the air, it has to go to zero percent humidity.
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Quote:
Originally Posted by Martinini View Post
Contaminated Fuel

Years ago we had serious fuel contamination problems due to underground steel storage tanks that rusted and leaked. Today all tanks are fiberglass, so this no longer happens (that I know of). However, those underground tanks do have fill plates on the ground surface (usually the parking lot) that can leak just like your boat deck plate. As the marina pumps its tanks nearly dry before the next fuel delivery, those who buy fuel from the near empty tank are the ones that are going to get the water (because it's pumped from the bottom of the tank). This despite the fact that the dock fuel pump has a water separating filter. I've opened the panels on occasion and have found the sight bowls completely filled with water, so at this point the water is being passed on to the customer. Next time you buy diesel, ask to see the filter at the pump! You have to remove the lower pump panel to see it.

However, it is important to note if you're getting water from your fuel retailer, chances are that it won't be a small amount. Most likely it will be a lot and your filters will fill up and engines crap out post-haste.
Just thought I'd comment on this bit and try to keep it non-technical (although I really should get some work done!):

Underground fuel storage tanks at marinas and service stations are typically double-skinned fibreglass; although aboveground ones can be fibreglass or steel.

When installed, the tanks are not level - one end is deliberately lower than the other. Fuel is either pumped from just below the surface (called "floating suction") or from near the bottom of the tank at the high end. At the low end is a sump with a sample drain. Over here (Down Under), for the Big 4 Oil Co's, the water drains are checked daily and any water pumped out - dunno what the regime is over there, but I assume it's the same.

The fuel bowser is fitted with a water-separating filter designed so that any entrained water is trapped at the bottom whilst the fuel flows out the side. The sight glass on these things shows the amount of water separated out of the fuel since last emptied. Some have an automatic cistern-style dump-valve that automatically drains the water away to a small holding tank when the sight-glass is full. Remember: The sight-glass is not an indication that water is being pumped in to your tank!

Pascoe is correct that if you get water from your fuel retailer, it won't be a small amount. If you're worried, check your tank each time you fill up and before you start the engine - but I'd think that the retailer would be more worried than you are to allow this to happen - he could get sued! - and would make sure his sample points are checked regularly.

Hope you find this helpful..
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  #18  
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Quote:
Originally Posted by noreault View Post
Its not the case that it condensation doesn't occur, its just that it is to little to be concerned about. Also the tank is not filled with air, it is air and fuel vapors.

By the way for all the water to condense out of the air, it has to go to zero percent humidity.
Noreault, the water is mostly in the fuel itself and not so much in the air - and a significant amount can settle out over time.

It doesn't take much of a slug of water in your fuel system to block the injectors and stop your engine mid-stroke.
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Old 06-23-2008
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Quote:
Originally Posted by SteveInMD View Post
Stillraining...actually water is a product of burning gasoline. It condenses in the cold exhaust system before the exhaust system heats up. As the system heats we see it exit as steam.
I did not know that...I guess that explains why my hands always feel wet if I use the exhaust to warm them....Thanks...
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Old 06-23-2008
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I get more than .81oz of condensate on my glasses when I come in from the cold. Any water is bad. It all accumulates at the bottom of the tank providing a great spot for those anaerobic microbes.
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