Run on reserve every so often

[KG]

Went out for a ride with a friend and he switched to reserve after we got fuel. He said every so often he switches and runs off reserve for about half a tank.

Gas floats on water so the water settles to the bottom of the tank and if you always keep the tank full enough to not have to switch to reserve then when you do you will get mostly water. And the water can rust out the bottom of the tank.

I never thought of it as I just use stabil or Lucas in the gas tank. What's says the more knowledgable master mechanics of the Dragon is it a good ideal or just another useless tech tip?

[fudgie]

I dont use resv if dont have to. Ive ran out before. 

I dont think there is enough water in your tank to make a diff. I always use B-12, seafoam, stp in my tank every month anyway.

[MarkT]

I could be wrong about this but most gas has ethanol in it now, which is alcohol which absorbs water.  So I don't think there's a puddle of water in the bottom of your tank.

[lee]

Use it or Lose it.

[Ricky-D]

Naw, Mark's right - no water in the tank.

***

[JetDriver]

Once the girl runs completely out of gas, there is still about ¾ gal of "unusable" fuel in the cracks, crevices, and low points of the tank.  If there is water in the tank, that's where it'll be.  If there's gas sitting on top of it, it's not going to rust- it needs oxygen to rust.  When I turned my tank over and shook out all of the gas (how I discovered the ¾ gal of unusable fuel), I had no water in it.  That's after 15 years of never being completely drained.  Barring unusual circumstances, I don't think you have to worry about water in the tank.

[98valk]

I always run to 100 mile (I/S tank) on reserve. there is always a chance of phase separation of fuel due to ethanol, fuel additives, heavier than the gas, any type of sentiment, etc., is helped to clean out.

[Valkpilot]

First off, let me say clearly that I think the use of ethanol as an "extender" of gasoline is a travesty.

I do think it is useful for preventing the accumulation of water in fuel systems.  I lived in northern Illinois and Indiana for most of my driving career and ethanol blends have been common there for a long time.  I never had an issue with any vehicle that could be related to these blends in close to 30 years.

It's actually difficult to accumulate enough water to end up with a layer of water in the tank, although it will happen sooner with conventional gasoline than it will with ethanol blends.  

Very little water can be absorbed by "pure" gasoline and so phase-separation (separate layers of water and gasoline) happens before it will in an ethanol blend.  In E10, the ethanol will bind to water up to 0.5% by volume (approximately 3.8 teaspoons of water per gallon of fuel) and keep it dissolved in solution until it it's carried out via combustion.  

Unless you spill or pour water into your tank, or suck it in from a contaminated tank at a gas station, it takes a very long time to accumulate enough from the atmosphere via condensation to phase-separate in your tank.  At 70°F and 70% humidity, it would take over two years to accumulate enough water through condensation and absorption to cause phase separation in an open one-gallon gas can.  It takes longer with ethanol blends. (it's something of a misnomer to say that alcohol "attracts" water.  It will absorb it by chemically bonding to it when present, but it doesn't leap up and grab moisture from the atmosphere.)

Here is the source of most of this data: Water Phase Separation in Oxygenated Gasoline  It's language is remarkably unbiased for a subject that is often attacked in the most transparently biased ways by both those in favor and against the use of ethanol in gasoline.

And the purpose of running for a while on reserve to remove water from the tank is somewhat lost on me.  As indicated above, it's not likely to be there anyway.  If done after a fill-up, the turbulence caused by filling the tank will have disturbed any phase-separated water that may have been in the tank and created a mixture of gas and water that will take time to settle back out.  If you have enough water present that running on the reserve will let it flow from the tank, you're risking  pulling non-combustible water into the chambers.  If you're worried that you have that much water in the tank, throw in a container of Heet (basically methanol to bind the water in solution with the gas), run the tank out, and refill with quality gas from a known station.

[Jess from VA]

Good post.   

[Farther]

Unless you spill or pour water into your tank, or suck it in from a contaminated tank at a gas station, it takes a very long time to accumulate enough from the atmosphere via condensation to phase-separate in your tank.  At 70°F and 70% humidity, it would take over two years to accumulate enough water through condensation and absorption to cause phase separation in an open one-gallon gas can.  It takes longer with ethanol blends.

One possible exception is that as ullage (empty space in tank/container) increases so does condensation.  Also, cycling through several cooling periods below dew point along with large ullage will increase condensation too.

[Valkpilot]

One possible exception is that as ullage (empty space in tank/container) increases so does condensation.  Also, cycling through several cooling periods below dew point along with large ullage will increase condensation too.

Correct.  Those things both increase the potential for water contamination, but it will still take quite some time to over-saturate the gas, especially E10, to the point of phase separation.  Months likely, not days or weeks (but faster in coastal or tropical areas.)  Any regularly-ridden bike should be pretty immune to water contamination through condensation.  

If it's going to sit, I make sure the there's fuel stabilizer in the tank and carbs, and that the tank is full of good gas.  (A 5 gallon tank full of E10 will need almost 1/2 cup of water added to it to phase-separate.)

If I knew it was going to sit for a VERY long time, I'd drain the carb bowls too.  In my opinion, varnish and gumming up due to evaporation is bigger risk than phase-separation.

I routinely run my bikes past reserve, sometimes to near vapor.  I think this helps keep things healthy.

[The emperor has no clothes]

Unless you spill or pour water into your tank, or suck it in from a contaminated tank at a gas station, it takes a very long time to accumulate enough from the atmosphere via condensation to phase-separate in your tank.  At 70°F and 70% humidity, it would take over two years to accumulate enough water through condensation and absorption to cause phase separation in an open one-gallon gas can.  It takes longer with ethanol blends.

One possible exception is that as ullage (empty space in tank/container) increases so does condensation.  Also, cycling through several cooling periods below dew point along with large ullage will increase condensation too.

That is true. "Back in the day" living in AK. It was prudent to keep your tank mostly full and to add heet. Otherwise the small amount of water would get in your fuel line and freeze and then you would be screwed in -30* and no vehicle or warmth. This hasn't been necessary for years though.

[Firefighter]

I like to top off my fuel after a ride, there is less air in the tank and less condensation. I can see lite surface rust in the tank opening ( what you can see while fueling), and want to do my best to keep any water out. I like to keep that metal area covered with fuel. I used to work on outboard boat engines, and the worst thing you can do is not use them. Unless your gone for months at a time I would at least start the bike and run it long enough to change the fuel in the carburetors often. I'm lucky, can ride year around.  Firefighter

[Gryphon Rider]

I learned a new word today! Ullage! Now if I can only remember it long enough to use it in Scrabble, then have someone challenge me on it. 

[Farther]

I learned a new word today! Ullage!

Good, I learn something new on almost all of your posts.

[larryh0841]

Running on reserve for the first 100 miles after filling the tank changes nothing as far as the gas source from the tank to the carburetors.  It is just the same gas flowing through a different port in the petcock.  There is no separate reserve space in the tank where gas is stored until the petcock is switched to reserve for use.     Larry

[KY,Dave (AKA Misunderstood)]

Ride lots of twisty roads which sloshes the fuel in the tank therefore keeping it mixed and no seperation 

[Daniel Meyer]

I hit reserve all the time...it's how I can tell I need to make a gas stop... 

[JetDriver]

Running on reserve for the first 100 miles after filling the tank changes nothing as far as the gas source from the tank to the carburetors.  It is just the same gas flowing through a different port in the petcock.  There is no separate reserve space in the tank where gas is stored until the petcock is switched to reserve for use.     Larry

That's correct, but the reserve port is right at the bottom of the tank, whereas the normal port is a couple inches above that.  Water and sediment weigh more than gas, therefore will be at the bottom of the tank.  If theres junk in the bottom, and you never go to reserve, you'll never suck that stuff through to the carbs, which is reason to me, if I was concerned, to never go to reserve.  I'm not concerned.