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

[Cusser]

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.

THIS !!!!

This information is from a "well-known" cussing chemist !!!

 

[Tornadoman]

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

A plastic gas tank will usually have very little if any condensation. A metal tank is a whole other story. Lots of condensation. That is why most, if not all manufacturers of anything use plastic tanks.

 

[Gord Baker]

Hmmmmmmmmmm. Possibly.

 

[ILENGINE]

A plastic gas tank will usually have very little if any condensation. A metal tank is a whole other story. Lots of condensation. That is why most, if not all manufacturers of anything use plastic tanks.

Because that is due to most plastic gas cans contain non vented filler necks with no other venting system. Hence the expanding and contracting of the side when the temps change. Metal with the same non venting design don't have water condensation issue either.

 

[Shady oak]

Isn’t condensation caused by the difference in temps between inside the tank, and outside, with a little bit of humidity thrown in? Condensation doesn’t leak in through a gas cap. Asking for a friend!

 

[ChiefH]

So explain to me how my 4 different chainsaws with 3 different brands can have fuel added in the spring of the year from a sealed container with no water visible and then set on an elevated surface in a storage shed over the summer and come September-October when I get the saws out to use them the first thing I have to do is dump the gas and water out of the fuel tanks. Normally I will get 1/4 in of water in the bottom of a mayo jar from each saw, Were did the water come from.

Now to some more of your thoughts. First thing is the tether on the gas cap is just that. Regulations require that the fuel cap be attached to the tank for the same reason that the fuel cap on your vehicle is tethered to the tank. And lawnmower fuel caps have either not be vented or have charcoal ventilation since 2012 so therefore no chance of air exchange.

Prior to 2012 caps were vented and some were thread vented and would wick water up the threads after a rain or heavy dew, Some had visible vent holes in the top of the cap that would allow dew and/or rain to enter directly. Had a customer with a 5 hp OHV Briggs horizontal Intek that was stored under a tub out next to the garden would end up with half a tank of water after a heavy rain.

So the issue may not be condensation as you think but the water is coming from some place,

I do not know why you get so much water in your gas chain saw tanks. I have one chain saw, one backpack blower, one hand held blower, one line trimmer, two walk behind lawn mowers, one shredder-chipper, one snow thrower, and I do not get water in any of the tanks. I DO however, refill the tank after use so that the tank has little room for air (ever air with moisture). I use Sta-Bil in all of my straight gas containers, and 2-cycle oil in my mix gas containers. I do not seem to get moisture in my storage containers. I live in a summer time humid area (Shenandoah Valley, Va.)

 

[farmerdave1954]

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

In 57 years of using every conceivable kind of lawn equipment, I have NEVER had a problem with water in a gas tank. NEVER. And the only thing I've ever done is take the OEM cap off, fill the tank, and put the OEM cap back on. No plastic wrap, no rubber bands, only using the OEM caps. I do try to keep the tank full on all my equipment, refilling after every use, especially when the machine is going to sit idle more than a few hours. As for not being much water in air at 100% humidity, stand out in the rain sometime and then tell me that with a straight face. ;-) But, in the small confines of a full fuel tank, there's not enough to worry about. IMO of course.

 

[Moparjoe499]

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.

If anyone is getting that much water in their tank, they should check their gas can for water. Don't keep to much gas stored and don't leave the gas can outside. I sold a coworker a push mower. She uses it and comes to work the next day and yells me the mower I sold her quit running. I go to her home and drain water out of the tank. I look for her gas can and find it sitting by her home. The gas can had water in it.

 

[Moparjoe499]

In 57 years of using every conceivable kind of lawn equipment, I have NEVER had a problem with water in a gas tank. NEVER. And the only thing I've ever done is take the OEM cap off, fill the tank, and put the OEM cap back on. No plastic wrap, no rubber bands, only using the OEM caps. I do try to keep the tank full on all my equipment, refilling after every use, especially when the machine is going to sit idle more than a few hours. As for not being much water in air at 100% humidity, stand out in the rain sometime and then tell me that with a straight face. ;-) But, in the small confines of a full fuel tank, there's not enough to worry about. IMO of course.

There is enough alcohol in today's gas to burn up the small amount of water. In my opinion, people are not checking their has cans and they are putting water in their mowers.

 

[Gord Baker]

Isn’t condensation caused by the difference in temps between inside the tank, and outside, with a little bit of humidity thrown in? Condensation doesn’t leak in through a gas cap. Asking for a friend!

Yes.