How to Keep Water Out of Your Fuel Tank

by Darren OBrien January 02, 2024

How to Keep Water Out of Your Fuel Tank

There is a common misconception among boaters in North America that because the gas and diesel we buy is essentially the cleanest in the world, we needn't worry about the dreaded "water-in-the-fuel" problem encountered in other countries. And though the fuels we buy in the U.S. and Canada are typically fine, once we have it in our tanks we still need to guard against water contamination and the subsequent problems those can manifest in our engines down the road.

Basically, if you have fuel tanks in your boat, you need to be aware of how water naturally infiltrates your tanks: through the vent line. The H2Out Fuel Guard is a very simple, inexpensive, and proven way to stop that from happening.

I was reminded of this issue having just finished recording another episode of our new podcast "The Boat Geeks" with Chuck Laguna of H2Out (video at the end of this article). We've known Chuck a long time, and H2Out even longer. I fondly recall being introduced to the original Fuel Guards, which were then called Air Vent Dryers, at the 2011 Seattle Boat Show by H2Out's inventor, the late Rich Pindell.

Rich was one of those people you just referred to as a "force of nature", and nature was one of his loves (along with science, engineering, and jazz music). He had developed and tested the Fuel Guard over two years and then announced the product to the recreational boating industry.

The following year it won the 2012 Pittman Innovation Award. In 2013 it was an Editor's Choice for Practical Sailor. But likely the biggest thing that could happen to the H2Out Fuel Guard was having Nigel Calder personally endorse the product.

We were selling H2Out Fuel Guards in our booth at the 2012 boat show and they were doing OK. It was still a new concept, and we had to explain the science and reasons why they should be on every boat that had fuel tanks. Then, seemingly at random times, we would get a crowd of folks coming to the booth specifically to buy them. Turned out that those rushes coincided with the end of Nigel Calder's seminars, during which he literally said any boat that had fuel tanks should have them!

Chuck called me back in 2019 to make a video with Nigel who was going to be in town for Trawler Fest. I'd met Nigel a couple of times, but was still very excited to work with him. After all, he is likely the world's foremost boat mechanics guru who gives seminars all lover the world. And he fiercely guards his integrity. In other words, he cannot be bought. Just listen to the first few sentences he says in the video we created with him:

 

OK, so this post is not all about Nigel. But his endorsement should speak volumes about the necessity of having Fuel Guards in the vent lines of your fuel tanks. 

That's because there are two main ways water can get into your fuel tanks through the air vent lines. The first is quite simple. As we use the fuel in our boats, the level in the tank drops. The space in the tank that used to be fuel is replaced with air. Where does that air come from? Through the vent line. What is the air made of? Moist, marine air. 

The second way is less obvious, and is called "diurnal breathing". This is the term for the natural daily airflow cycle of your fuel tank. The air vent line allows this. During the day, the fuel in the tank expands due to the warmth of the ambient temperature. This pushes out last night's air. Then at night, when the fuel cools off and contracts, fresh marine air full of water vapor is sucked back into the tank. This is how boats that sit unused for long periods of time can still be adversely affected by water contamination.

Whether your boat is used regularly or sits all winter, an H2Out Fuel Guard spliced into the vent line will immediately begin keeping water vapor from getting into your fuel tank. The stainless steel canister is filled with silica desiccant that adsorbs water molecules, with only "dry" air emerging and into your tank. Notice I used the word aDsorb, and not aBsorb. What's the difference?

The main difference is that while aBsorption involves the mass transfer of particles into another material (one substance absorbing another), aDsorption takes place with the adhesion of particles onto the surface of a susbtance. In other words, water molecules adhere and become part of the desiccant. With absorption, the water molecules are soaked up (with a sponge for instance) and eventually need to be squeezed or drained out. Which, of course, would not work in something like a fuel tank vent line.

During the initial testing of the product, inventor Rich placed Fuel Guards on two different tanks of B100 biodiesel. Both petroleum-based fuels and bio-fuels attract water molecularly, but the bio-fuels are much more hygroscopic, readily attracting and retaining water vapor from the atmosphere. Thus, biodiesel made a better test as it is more vulnerable to contamination by water.

He tested two tanks of diesel. One a professionally stored tank of fuel, and the other a partially filled 55-gallon drum left outside in his back yard through an entire Pacific NW winter. Its only protection was an H2Out Fuel Guard. The results were astounding.

 

The jar on the left, with fingers clearly showing through, came from the Fuel Guard protected drum. This is the way your diesel should look: fresh, clean and dry. The jar on the right shows fuel from the professionally stored tank without any protection. A well-contaminated layer of sludge has sunk to the bottom of the jar, and the bottom of the water layer (remember diesel, gas and oil float on water). The murky dark layer on top is contaminated fuel.

As soon as the boat moves or the engine is started, the layers of fuel, water and sludge can become mixed and then pulled into the engine. This can ultimately cause engine corrosion and clogged injectors, which can be very expensive to fix. In the wrong place and at the wrong time, engine failure can also be dangerous.

On our boat, which can carry 820 gallons of diesel in two tanks, we only buy high quality ValvTect marine fuel (same for our gas outboard). However, no matter how good the fuel is when you buy it, we still need to protect it from water contamination. Thus the need for H2Out Fuel Guards.

Research has shown that the desiccant in a Fuel Guard will continue adsorbing moisture up to 3 years on diesel tanks, and 5 years on gas tanks. "Re-arming" your Fuel Guard is very inexpensive and easy with Replacement Media packs. Simply remove the top of the anodized aluminum canister and dump out the beads of desiccant. They are completely harmless and can be thrown away like household trash. Refill the canister with new replacement desiccant and place the Fuel Guard back into the vent line. Chuck simply replaces his annually, a practice we follow as well.

As our friend Andy Keenan of KTI Systems (inventor of the Filter Boss fuel filtering systems) famously says when it comes to engine problems in our boats it's usually due to one of three things: fuel, fuel, or fuel. There simply is no better and more affordable way to protect your fuel and engines than the award-winning H2Out Fuel Guard.




Darren OBrien
Darren OBrien

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