Full tank vs. stale gas ?

[Rick_Powers]

I'd be curious to hear what people think.

1) Is is better to keep a full tank of gas to prevent moisture in the tank, or is it better to keep it low so that fuel does not sit unused for too long.

Also:

2) If it is not a myth that gasoline goes bad over time, then what happens to it? Does it change molecular structure, or does it absorb bad things like moisture?

Thanks!

[adab1402]

time waits for no fuel

hi rick gas does break down over time ,i suggest ,if your not sure of its age ,a)take a sample and have it analyzed or my choice B)drain it all out throw it into a rig,car, truck etc and fill the rig with new fuel ,unless its obviously bad , mixing in your car will use it up much faster .now back to the boat , fill it full of clean fuel ,good filters and a fuel stabilizer from west marine ,write down the date in your mechanical log .and yes it,s better to keep that rascal relatively full 2-3 inches from the top . fair winds adab1402

[Dave O]

The original A4 manual (for me that is 1978) recommends filling the tank with gas at the end of the season and topping up with a stabilizer as described by Adab. That's what I do.

To be sure I then drain the fuel system downstream of the tank including the fuel hoses, the Racco filter, the polishing filter and the carb.

I don't know about the chemistry you note in point #2 but this seems to work for me.

Dave

[knitchie]

Full tank vs. stale gas ?

Of course, ethanol has thrown a whole new variable in the mix since our old A4's were installed. I still don't understand all the issues involved with that. I top off my tank when I get hauled each fall, but am always ready to change that practice based on better information.

Editorial comment: I really wish that ethanol would just go away. It may help corn farmer's incomes, but it is a very inefficient method of reducing fossil fuel use, 5-10% at best before it is mixed in with gas. Translation: It takes 0.9-0.95 gallon of fossil fuel to make 1.0 gallon of ethanol. Then, when you mix that one gallon of ethanol with 10 gallons of gas, you only get a 0.5-1% reduction in fossil fuel use. I'd rather eat my corn and find real reductions in fossil fuel use elsewhere.

[domagami]

Topping off gas for storage

Hi Rick, all -

A two or three years ago the Boat US magazine had a nice summary article on this - might be in the archives on their website. You can also find some information on this sort of thing from the major retailers, I think I found some information on the BP site.

Anyway, like your question, it has been the source of endless (and completely uninformed) October debates with my in-laws. Finally I just distributed the material I found. The short of it is this:

For winters it is suggested you just about top off the tank, rather than leave it empty or half full. The reason has more to do with the air space than the volume of gas. You want to minimize or nearly eliminate that amount of air in the tank.

The void with air also contains moisture. The more air, the more moisture. Over time, the gas will draw the water out of the air into your gas. Not good. Filling the tank minimizes the amount of air, and thus less water in your mix.

Ethanol blends just make all this worse. The alcohol is actually better than gas at drawing water out of the air. So not only is E85 less efficient, and destroys some kinds of tanks, it also makes the water problem worse.

One other suggestion I found is to leave a bit of space for expansion. (I think I read 5%) The rationale was that if you were topping off when you put the boat up and it was 40 degrees (as we do up north), and then don't get to drop and run it in the spring until it's over 60, you may end up with expansion and a gas being forced out of ... well, where ever it can.

(And I think it was concern for expansion when the tank warmed, rather than expansion when it cooled over the winder - as water does during freezing. Either way, it will expand while you're away.)

All that said. I would love to hear if someone has heard anything to the contrary.

Best to all,

Mick

[vabiker23518]

Could not have said it better than Knitchie...ethanol is a bad joke the politicians have forced on us.
I keep my tank full, and use STABIL addative. So far so good. I also use STABIL on all my mowers and tractors and they always start and run well in the spring.

[policecentral]

This will probably raise a fuss, but...

Years ago I decided to not worry about stale gas and condensation. I drained the onboard gas tank that holds about 30 gallons. Then, I got a sturdy five gallon gas can, and attached an internal syphon tube and gas line connector. This "portable" gas can is lashed in the port side lazarette.

To fill, I simply remove the can onto the dock and top off. This means that I do day-sailing with five gallons on board, and the more frequent refilling assures relatively fresh gasoline. For extended cruising, I simply reattach the gas line to the larger tank and fill up. I have had absolutely no problems with heeling, spilling, gas fumes etc. My bilge blower also ventilates that lazarette. Whenever necessary, I can completely empty the "fiver" and start with fresh gas -- of course complete with MMOil.

It's a great solution that works for me -- no condensate, and no stale gas, and I believe less tendency to varnish the carburetor. Coast Guard did vessel inspection recently and did not say a word...


Policecentral
Ranger 30 Northern Light
Savannah, GA

[Kelly]

No fuss from me, I'm just wondering what exactly is the "internal siphon tube"? Is it just the pick-up tube for the outgoing gas? And is the five gallon tank vented somewhere overboard or does the blower take care of that for you?

This comes back to the discussion earlier about expanding and contracting volumes. Are not all below-deck tanks vented to the atmosphere, thereby preventing problems such as these?

Kelly

[domagami]

vented

Kelly -

Duh! (smacks self in forehead) You are right - I completely neglected to consider the vent when considering any expansion. For our boats this is clearly not an issue.

MD

[CalebD]

Just to stir up the pot a bit...

David Pascoe makes the argument that filling the tank up with fuel for layup is a myth:

http://www.yachtsurvey.com/myth_of_condensation_in_fuel_tanks.htm

That said, we keep our tank mostly full over our winter layup. The only time we had an issue with doing this was when the tank was filled up to high and come the spring thaw there was some fuel leaking out of the tank vent on the transom.

[policecentral]

Internal siphon tube

Right, the "siphon" tube is internal and is a "pick up" tube extending to the bottom of the gas can. I used a piece of 1/4inch copper, soldered onto the fitting that I installed in the top of the can. For ventilation, I simply crack the screw-top open, and tighten it back when I shut down. All of the issues discussed here, stale gas, varnish, moisture, dirt in the tank, etc. are history. Think of the troubles gone: dirt in carb, water in the carb bowl (which will rust through), moisture in gas causing erratic running, etc. By the way, I also installed an in-line filter, too.


Policecentral
Northern Light, Ranger 30
Savannah

[roadnsky]

Pictures?

Jim-
Do you have a picture of your 5 gal setup?
-jb

[joec43]

half full or half empty?

As any long haul trucker knows, when you take fuel from a hot climate (summertime) to a cold climate (wintertime) and the tanks are not full, the moisture in the air will condensate and turn to water.
Thus, methyl hydrate is introduced to get rid of the moisture (now water) in the fuel. Unless, of course, you fill up with winter fuel in the cold climate. We don't do that in our boats.

So, if your tank is completely empty, the moisture in the warm air will condense when it gets cold, and you will get some water in the tank.
If your tank is half empty, the moisture in half the tank of air will get some condensation, and some water will get in the tank.

Now with ethanol, which will absorb and mix with water up to 30% by weight and form an emulsion, it will not freeze, but will absorb the moisture. Would need a scientific calculator to work it all out, but it certainly introduces some interesting thoughts.

Bottom line for me is, keep the tank full over the winter. No air, no moisture. A little bit of stabil to keep it good.

Will gas go bad over time, absolutely! Ask anyone who stocked up for the Y2K bug. But when it goes bad, it smells just like varnish, and will solidify in your injectors (car), carb, and lots of other places. Took mine 5 years to go like that.

As you can see, I'm bored here on the mooring field in Key West, waiting out high winds, anxious to get moving.

Joe

[sastanley]

Joe...can you see the S/Y "Legacy" from your location? Two years ago when I was there, it was still stuck on the marsh when Wilma had blown it there.

This past year when I was there, it had moved kinda to the northern end of the mooring field.

Apparently now, it is sort of floating, but I read somewhere that the keel dropped and it is aground at anchor.

[joec43]

boat on her side

I believe I can see it, although I can't read the name. I can't take the dingy over there, its too shallow, and the winds are still 25+ knots. My old British Seagull outboard only does 3 knots, so it would be a horrid ride.

She's the only boat on her side there, looking totally derelict.

I will try the max zoom on my camera and take a photo, pm me your email, I'll send it along.

Joe