Gas Caps do seal out any condensation from entering the gas tank, despite the arguments here saying they do not

[Rivets]

Boy I hit a nerve. I just call them as I see them. I may not be right, but you also could be wrong. Let others who read this thread make their own decisions when they get both sides of this theory.

 

[bertsmobile1]

We had a fishing boat ( small one ) with an outboard and a sealed fuel tank so every now & then you had to pump it up

 

[Hammermechanicman]

We had a fishing boat ( small one ) with an outboard and a sealed fuel tank so every now & then you had to pump it up

Sounds like one of the old 50's era Evinrude dual hose system that used air from the engine to pressurize the fuel tank. Haven't seen one of those for a few years.

 

[bertsmobile1]

It was 10th hand throw away
dad had an old pulling boat of the 12 oars x 2 men per oar
It was a very sturdy boat but a real hand full single handed
I got an old victa lawn mower outboard conversion in bad shape but the 125cc engine & 4" prop did not give much of a push.
don't know where the outboard came from all I remember was it was 2 strike, would either foul the plug or whisker the plug & the fuel tank was similar to a race car it was a stand alone can with some pipes & a bulb pump that was forever perishing

There is a good reason why I took up motorcycle riding.

 

[Moparjoe499]

The gas cap is believed by some that even when screwed on tight, still allows for condensation to enter.

There is an article on IFishFishing Forum, & I'll quote from it:

There isn't enough air volume within a tank to hold much vapor.
On average, tanks are half full, further reducing volume
The amount of water vapor in air is very small, even at 100% humidity
Conditions aren't right to cause condensation in a fuel tank.
_________________________________________________________________

This makes the most sense to me. how can condensation (moisture) penetrate through a tightened on gas cap?? Please, if you have some logical rebuttal to this, then post it.

Assuming, I'm wrong & IFishFishing author are wrong, the same posters who believe gas caps don't keep moisture out recommend to take a piece of plastic wrap & place it over where you will tighten the gas cap. However, at least in Craftsman mowers & I would think other mowers have the same design, it DOES NOT WORK because there is a string coming out the bottom of the gas cap, and at the other end of that string is a U-shaped large piece that hangs in the tank, & you have to turn it sideways to get it out of the tank. End result is you are holding a gas cap with a string. I don't understand its purpose other than it is a way of telling you, if the U-shaped piece is not completely submerged in gas, that you need to add fuel. This whole design is IMO ridiculous. Just have a gas cap without this extra nonsense of strings & U-shaped pieces. If the user can't use a flashlight to look in the tank & see the level, then they should hire a lawn service.

So, NO plastic wrap for me. A friend of mine suggested just placing the plastic wrap (or better a zip lock bag) over the hole & use rubber bands to keep it on and seal any outside condensation from entering. IMO, this is just too much of a hassle. If you want to take this to extremes, take a good size piece of plastic wrap. Place it over the entire tightened gas cap, & use an appropriately sized rubber band to seal it to the top of the gas tank's tube.

If you disagree, please post with something other than just stating that gas caps are not airtight & allow moisture through. You should read the article, "THE MYTH OF CONDENSATION IN FUEL TANKS"

The Myth of Condensation in Fuel Tanks

www.ifish.net

If you use a mower often enough, there is no need to be concerned about condensation.

 

[Moparjoe499]

Looks like another great internet debate. Just me, I store my zero turn completely full. Everthing else is empty and run dry. Never have a water problem. Probably a quarter of everything customers bring in have some water in the tank. I dump every handheld, push mower, tiller and snowblower that comes in. I see lots of water.

A couple weeks ago I started a snowblower that had been sitting in my garage for 6 years. I ran it for 5 minutes without any problems. People get all anal about the fuel worrying about if the cap has a good seal, draining the tanks dry, putting fuel stabilizer in the tanks, ect, ect. Unless you are purchasing 100% gasoline, then it already has 10% alcohol in it and the water will be burned when it is running.

 

[Moparjoe499]

Yes water can get in tank with fuel caps as they do vent inwards. And some do go bad too. Just had a tiller earlier that I put on a new carburetor with new fuel lines and new fuel. It came back a month later with water damage to the new carburetor. I found a bad fuel cap allowing rain water to enter via the vent hole.

And with ethanol fuels water vapor will combine with the fuel and then settle out as water. Small amounts at first until it builds up over time. Most is not noticeable as we are normally using our during the mowing season. It when they sit for extend periods that this settled out water seeks the lowest point which with gravity fed carbs is the carbs itself. Once there corrosion happens.

Besides most water get introduce from poorly sealed containers just like grass and other trash in fuel does. I rarely find in my eqiupment unless I get bad fuel from the local station which is why I quit them. There tanks has caps on them too but had a bad one that finally got replaced.

I have never had a problem with water in the fuel. I have some methanol left over from drag racing. That should take care of any water.

 

[Cajun power]

The gas cap is believed by some that even when screwed on tight, still allows for condensation to enter.

There is an article on IFishFishing Forum, & I'll quote from it:

There isn't enough air volume within a tank to hold much vapor.
On average, tanks are half full, further reducing volume
The amount of water vapor in air is very small, even at 100% humidity
Conditions aren't right to cause condensation in a fuel tank.
_________________________________________________________________

This makes the most sense to me. how can condensation (moisture) penetrate through a tightened on gas cap?? Please, if you have some logical rebuttal to this, then post it.

Assuming, I'm wrong & IFishFishing author are wrong, the same posters who believe gas caps don't keep moisture out recommend to take a piece of plastic wrap & place it over where you will tighten the gas cap. However, at least in Craftsman mowers & I would think other mowers have the same design, it DOES NOT WORK because there is a string coming out the bottom of the gas cap, and at the other end of that string is a U-shaped large piece that hangs in the tank, & you have to turn it sideways to get it out of the tank. End result is you are holding a gas cap with a string. I don't understand its purpose other than it is a way of telling you, if the U-shaped piece is not completely submerged in gas, that you need to add fuel. This whole design is IMO ridiculous. Just have a gas cap without this extra nonsense of strings & U-shaped pieces. If the user can't use a flashlight to look in the tank & see the level, then they should hire a lawn service.

So, NO plastic wrap for me. A friend of mine suggested just placing the plastic wrap (or better a zip lock bag) over the hole & use rubber bands to keep it on and seal any outside condensation from entering. IMO, this is just too much of a hassle. If you want to take this to extremes, take a good size piece of plastic wrap. Place it over the entire tightened gas cap, & use an appropriately sized rubber band to seal it to the top of the gas tank's tube.

If you disagree, please post with something other than just stating that gas caps are not airtight & allow moisture through. You should read the article, "THE MYTH OF CONDENSATION IN FUEL TANKS"

The Myth of Condensation in Fuel Tanks

www.ifish.net

the myth? lol....with years of proof that this is no myth you are going to expect anyone to accept that water ingress into fuel tanks is not a thing?

Lets start with some basics. gasoline is generally not water attracting..but the gasoline sold and used by almost all mower owners contains alcohol, which does attract water.

the cap bs and the volume bs. A rest, your assumption is that the volume is too small to make a difference and that the cap vent is either too small or that is provides some kind of one way valve protection against water vapor/condensation. So several things: 1) the tank vent is designed to release pressure build in the tank AND also to PREVENT negative pressure (vacuum), so it really is a two way valve. It's designed to be an "OPEN SYSTEM" operating to prevent fuel vapor from building up dangerous high pressure in the tank and also preventings a negative pressure a vacuum in the tank as the engine is operating. Whether this is a gravity fed fuel engine or a pump fed fuel engine, the design is the same. It's a two way valve. And this also occurs IN STORAGE. Because you see, the temperature ambient is also going to cause fuel vapors to expand and contract. And thus even in storage, this valve is constantly moving from open to close, close to open..ever so slightly, but over time, yes, this is going to allow water vapor from the atmosphere (AND CONDENSATION THAT FORMS RIGHT AT THE EDGES OF THAT VENT) to be entrapped and to enter the tank. Water vapor is heavier than fuel, and heavier than fuel vapor..so you have a density issue and this results in fuel vapor going to the bottom of the tank, below fuel. In this area, it accumulates because it cannot escape the lighter density of fuel vapor and fuel liquid on top. Over TIME, this also happens with fuel cans that you use to fill your fuel at the pump. When you open the cap on your portable fuel tank, you are allowing the inrush of fuel from the pump into a quite large opening..it is during this moment when you actually have a very interesting water vapor introduction into the fuel and into the fuel can. Also, one must understand that even at fuel stations, there is a certain amount of water contamination as well. Especially for gasoline sold as alcohol mix. For most vehicles, this small amount of water/water vapor is not really a problem, because auto engines are actually engineered and designed to operate with small amounts of water contamination and still be reliable. However for small engines, air cooled, small amounts of water/water vapor has a much greater impact over time.
Here is an easy experiment you can prove for yourself.

fill your mower tank half full with gas. let it sit for 3 months over the winter. At 3 months, drain the tank completely in a glass mason jar. Notice the fuel-water separation. That is just reality.

now the argument about how much damage can happen with water in fuel? that's a separate question, but important nonetheless. Over time, especially with long storage fuel, water becomes a problem associated with rust and corrosion and also tends to cause fuel lines to become brittle or to collapse internally. Some fuel filters also have different metal components and water creates dissimilar metal corrosion internally, just as it will do with carbs...it's the water that becomes the ion transport, not the fuel...almost all carb contamination from corrosion is caused by water/water vapor. what can you do about it? again, another separate question. It's actually a good practice to NOT STORE Fuel in a tank or a carb for long periods. I do this by emptying the tank and running the engine until it starves from fuel and then I open the carb and allow it to dry, and open the fuel lines too. I smoke the head cylinder with a little motor oil, and then put it all back together. When it comes out of storage, the tank is filled with fresh fuel, and I drain about a 1/2 pint of it out of the fuel line right before the carb...into a glass mason jar. I look for contamination and water vapor. because you see EVEN IN AN EMPTY FUEL TANK< WATER VAPOR CAN HAPPEN. it's a combination of hot/cold weather and that tank vent which is a two way valve...water Can and does accumulate there even when it's empty. This is particularly true for the deep south where high humidity is a year wide environmental reality.

 

[Gord Baker]

The gas cap is believed by some that even when screwed on tight, still allows for condensation to enter.

There is an article on IFishFishing Forum, & I'll quote from it:

There isn't enough air volume within a tank to hold much vapor.
On average, tanks are half full, further reducing volume
The amount of water vapor in air is very small, even at 100% humidity
Conditions aren't right to cause condensation in a fuel tank.
_________________________________________________________________

This makes the most sense to me. how can condensation (moisture) penetrate through a tightened on gas cap?? Please, if you have some logical rebuttal to this, then post it.

Assuming, I'm wrong & IFishFishing author are wrong, the same posters who believe gas caps don't keep moisture out recommend to take a piece of plastic wrap & place it over where you will tighten the gas cap. However, at least in Craftsman mowers & I would think other mowers have the same design, it DOES NOT WORK because there is a string coming out the bottom of the gas cap, and at the other end of that string is a U-shaped large piece that hangs in the tank, & you have to turn it sideways to get it out of the tank. End result is you are holding a gas cap with a string. I don't understand its purpose other than it is a way of telling you, if the U-shaped piece is not completely submerged in gas, that you need to add fuel. This whole design is IMO ridiculous. Just have a gas cap without this extra nonsense of strings & U-shaped pieces. If the user can't use a flashlight to look in the tank & see the level, then they should hire a lawn service.

So, NO plastic wrap for me. A friend of mine suggested just placing the plastic wrap (or better a zip lock bag) over the hole & use rubber bands to keep it on and seal any outside condensation from entering. IMO, this is just too much of a hassle. If you want to take this to extremes, take a good size piece of plastic wrap. Place it over the entire tightened gas cap, & use an appropriately sized rubber band to seal it to the top of the gas tank's tube.

If you disagree, please post with something other than just stating that gas caps are not airtight & allow moisture through. You should read the article, "THE MYTH OF CONDENSATION IN FUEL TANKS"

The Myth of Condensation in Fuel Tanks

www.ifish.net

Air contains Moisture. A Fuel Tank MUST be vented to allow fuel to flow out, thus fresh air is being constantly drawn into the tank. Covering the fill neck with plastic will help with that if it is a tank not being used for an engine. To store Fuel, fill the tank to the Top and keep in a cool dry place. Try to use it within 30 days and refresh tank. Ethanol absorbs Moisture. That is the big problem.

 

[Gord Baker]

I have never had a problem with water in the fuel. I have some methanol left over from drag racing. That should take care of any water.

Be careful with the Methanol. It can seize plastic shutoff valves etc.