Diesel Tank Vent Filters - Practical Sailor (2023)

Diesel Tank Vent Filters - Practical Sailor (1)

Over the last two years, Practical Sailor has dug deeply into ways to keep gasoline and diesel fuel tanks healthy. Weve investigated ethanol phase separation, anti-corrosion additives, biocides, and gasoline-tank vent filters (PS, January 2013, February 2013, and August 2013). We’ve learned that while effective additives can help, the bottom line is that clean, dry fuel is the only sure path to fuel-system protection and reliability.

The most common way for water to contaminate fuel is through leaky fill caps-this is particularly disconcerting because corrosive salt water is in the mix. Boat owners should inspect the fill cap O-ring regularly, and replace it early. A light coating of Vaseline will prevent sticking and help repel water. Any flowing water-rain or sea water-should be diverted away from the cap with rails or by relocating the fill cap.

Wet fuel can also come from the fuel dock as either free water or as water-saturated fuel. Neither should be surprising, given how many coastal tanks have gone under during storms.

Water can also enter through the fuel tanks daily vent breathing. In the January 2013 issue, testing showed that free water can condense and fall to the bottom of fuel tanks, primarily in cool, damp weather, but we also know that substantial dissolved water can be present in warmer temperatures-not visible, but still working its mischief. During long winter storage, perhaps, daily breathing is the most significant cause of water getting into fuel. It is this water source that can be stemmed by installing a fuel-tank vent filter.

Through lab tests and several years of field testing, we’ve found that silica-gel vent filters reduce tank corrosion and improve gasoline stability. But is the same true for diesel fuel and tanks? Thats what this test sought to find out.

Diesel Tank Vent Filters - Practical Sailor (2)

What We Tested

When we launched this test, there was only one vendor of diesel vent filters marketed for marine use, Pindell Engineering. The first in the marine desiccan’t business, Pindell offers its diesel tank vent filter in two models: the AVD2 for tanks up to 60 gallons and the AVD3 for tanks up to 200 gallons. The AVD2 contains 17 ounces of silica gel, and the AVD3 has 34 ounces.

The AVD filters are suitable for diesel or gasoline, and the H2Out AVD2 was testers Best Choice pick in our recent test of gas tank vent filters.

(Video) FilterSavvy - Baldwin Filters - Fuel Filters 3

The filters can be installed in any orientation. The silica gel changes from blue resin to pink once about 70 percent of the available adsorption capacity is spent. The color change is easy to see through the housings clear Lexan shell. To remove the spent silica, simply remove a hose clamp on one end and dump it out, but doing this neatly requires removing the housing from the line in most installations. The AVD2 retails for $129, and the AVD3 costs $189. Refills, available through Pindell, cost $30 for the AVD2 and $40 for the AVD3.

Since that test, Vetus Engineering launched a new tank vent filter that would be compatible with diesel, as well as gas. Unlike the Vetus No-Smell NSF16 we tested in the gasoline filter comparison, the new No-Smell NSFCAN will use a combination of activated bulk carbon and bulk silica gel as its adsorbent media. This approach is similar to the experimental filter PS testers constructed for the gas filter test, using the NSF16 housing and bulk silica gel. We plan to test the new Vetus filter once it is released.

Could a sailor build his own fuel-tank vent filter? Because of safety issues and materials compatibility issues, we are going to leave that question to the engineers. PS testers used PVC pipe to construct mini filters for the test, but PVC should not be used in on-board installations; PVC glues do not adequately resist petroleum, and the no-hub, flexible PVC fittings available in hardware stores are not suitable for use with petroleum. Could a boat owner adapt an industrial version? Perhaps, but there are design issues that prevent our recommendation-they often contain fine filters that can plug and endanger the vent function; they are often designed only for vertical installation; and some are not diesel compatible.

How We Tested

For lab testing, we selected a bundle of metal coupons (samples of standard alloys prepared into 1-inch by 2-inch rectangles with a hole in the center for mounting) used in ASTM method D1384, a method for evaluating engine coolants. We modified the ASTM test to serve our purposes. This approach ensures uniform metal alloys of known composition. Additionally, the coupon bundles are designed to mimic the galvanic corrosion effects common to units assembled from dissimilar metals. The couplings used were aluminum/steel/brass (to mimic a poorly assembled fuel system, since brass should not be coupled with aluminum, but we have seen it done) and copper/steel (to mimic a steel tank and typical fuel systems).

We filled three 1-liter bottles with 300 milliliters of ultra-low sulfur (ULS) diesel from a busy retailer, placing a metal corrosion bundle in each bottle. The tips of the coupons were left exposed to ensure some air exposure. One bottle was sealed to serve as a control; another was vented through 10 inches of 3/16-inch ID vinyl tubing; and one was vented through a PVC mini-vent filter containing 6 milliliters of commercial-grade silica gel (from H2Outs AVD3 vent filter) and a tail of 7 inches of 3/16-inch ID vinyl tubing. This laboratory vent filter was sized to be proportional to an ADV2 fitted to a 30-gallon tank; however, we exposed the samples to greater temperature swings (due to their small mass) and a shorter vent hose than real-world installations, creating a scenario where the vent filter began to fail during the shortened test period; seven months of exposure in our test setup is comparable to three to five years of real-world exposure. The tested vent filter was exposed until the silica gel was 70 percent spent, as shown by its color; this took from December through July in typical Chesapeake Bay-area weather.

To get some real-world data, testers installed two H2Out AVD3 vent filters aboard test boats equipped with 75- to 100-gallon fuel tanks; the boats are kept in the water year-round.

Diesel Tank Vent Filters - Practical Sailor (3)

Lab Test Results

The photographs tell the story. The diesel fuel in the test setup with the vent filter remained clearer and contained less sediment than the free-vented or sealed samples. It seems that the silica gel actually dried the fuel, relative to the sealed sample-this was something we also observed in testing gasoline tank vent filters. There was a thin layer of pink, spent resin on the fuel-tank side of the filter, as well as a thick pink layer on the atmosphere side of the filter, with only a thin layer of blue resin separating the two.

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The discoloration of the fuel was the result of the metal coupons corroding, which was due in part to the presence of air and water in the test setup. Another catalyst was the disproportionate amount of copper; copper can cause fuel to polymerize and gum.

While the discolored fuel was evidence enough of corrosion, the degradation of the metal coupons was more dramatic. Testers rated the sealed test sample as fair, and the sample with the vent filter was pristine, but the free-vented sample displayed serious corrosion, including major pitting of the steel coupons. The aluminum coupons were unaffected. The small size of the samples certainly exaggerates these trends, but the findings are very clear: Dry air and dry fuel mean less corrosion and less fuel deterioration.

Field Test Results

So far, our field-test data suggests that Pindell Engineerings recommendation that the desiccan’t media in the H2Out filters be replaced about once or twice per season, is extremely conservative. In one year, we have seen almost no color change in several installations, and we believe two to six years is possible, depending on the vent configuration, tank size, fueling practices, and geography.

These results are in stark contrast to our e-10 gasoline testing results, which indicated that the ethanol present enables the silica gel to self-regenerate, allowing one refill to last at least several years. However, the cost and effort to replace the gel in the H2Out filters is minimal. The clear polycarbonate filter housing makes it easy to inspect the silica gel and to see whether it has changed color. Silica-gel resin is available through Pindell Engineering or from commercial desiccant vendors at significant discount.


The H2Out AVD vent-filter line performs well in diesel fuel systems, and the filters deliver value. Users will need to replace the media every few years, when the media color changes, at a cost of $15 (from Delta Adsorbents) to $40 (Pindell). The service cost can be justified as it can prevent a potential tank or engine repair down the road, then its financially smart. If on-the-water reliability matters, then its a very simple decision. An annual media inspection before winter storage would be a sound practice, as any remaining fuel will be sitting for a long period.

For a sailor who doesn’t burn through a single tank in a year or who doesn’t want to top off a tank with fuel that will only sit for another year and grow stale, a vent filter is one option, but full tanks help too. Anything you can do to preserve fuel quality is a benefit.

Fuel Systems Tips & Techniques

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Does a diesel tank need a vent? ›

Bulk diesel storage tanks should be equipped with a vent line to prevent vacuum formation or overpressure in the tank during drawdown or tank filling, or due to atmospheric temperature changes.

How does a diesel fuel tank vent valve work? ›

A diesel fuel tank breather is a valve apparatus that is connected to a fuel tank vent, which enables the tank to 'breathe'. It allows for the optimum intake of air as fuel is released from the tank, and expulsion of air as fuel is deposited into the tank (or expands within the tank).

What does a holding tank vent filter do? ›

This activated carbon filter will keep your boat smelling clean and pleasant. Fits inline in your breather hose. Connections suitable for 19mm or 25mm breather tube.

What are the two types of filters are used in a diesel fuel system? ›


In series filters, all the fuel goes through one filter and then through the other. In parallel filters, part of the fuel goes through each filter.

Do fuel storage tanks need to be vented? ›

Generally, codes require vents for tanks containing flammable and combustible liquids that are installed in buildings, including storage tanks, day tanks on pumps and generators, etc., to be extended to discharge outside.

Why do diesel tanks need earthing? ›

Tanks and Vessels

Ground the shell of tanks that contain flammable products and those without flammable products but located in a hazardous area. Grounding the shell drains the outside charge but does not remove the chance of sparking inside the tank.

Which is a risk of a clogged fuel vent? ›

The fuel tank may build excessive pressure due to a blocked vent. This could cause fuel to spray on occupants or bystanders when opening the fuel cap, potentially causing injury. Additionally, if an ignition source was present, this could create a risk of fire, causing injury and/or damage to property.

How does a rollover vent valve work? ›

The fuel tank rollover check valve works by way of a ball or spring inside that allows pressure and vapor to escape the fuel tank when changes in temperature occurs. The Ball in the valve moves to the closed position when the vehicle experiences a rollover; in effect cutting off fuel from exiting the tank.

How does a roll over vent work? ›

Used in conjunction with your vent line, a rollover valve will allow your tank to breathe and not build up pressure or vacuum during normal operation. Remember, as fuel is added to your tank, air in the tank is displaced and has to go somewhere.

How do you vent a holding tank? ›

A holding tank vent must be located above the heeled waterline (usually led from a high point in the plumbing). Use commonsense when choosing the location: Place it away from the cockpit and galley ports.

How do you vent a sewage tank? ›

The ejector tank should be vented by a connection to the top cover that's at least 1 1/2 inches in diameter, although 2-inch vent pipe is common in this application. The tank vent should be a dry vent that either terminates at the exterior of the house or connects to another dry vent that terminates at the exterior.

What micron filter is best for diesel? ›

Recommended Best Practices

While the DFQC report recommends that fuel site operators use 10-micron filters to capture smaller particles in diesel, 2- or 5-micron dispenser filters will provide the greatest protection.

Which is better 2 micron or 30-micron? ›

Racor recommends that a 2-micron filter only be used in final or secondary filters where the fuel is first filtered by a primary filter. Further, the company says a 30-micron filter should be used as a primary to filter raw or poor-quality fuel before it is further filtered by finer media, such as a 10- or 2-micron.

Which filter is better 5 micron or 10 micron? ›

A 5 micron rating works well in many industries, including the food and beverage industry. This rating filters a little less than the 5 micron rating. Filters with a 10 micron rating can remove some unseen materials from liquid but not bacteria or viruses.

What causes vacuum in tank? ›

The most common cause of vacuum in tanks is caused by steam (water vapor). When you fill a tank with water vapor, most of the air is pushed out of the tank. As the water vapor cools, it condenses into liquid water. Now you have a little bit of liquid in the tank instead of a large amount of water vapor.

Why is the fuel tank venting controlled on a modern vehicle? ›

Fuel tank vent systems are common features on diesel trucks and fuel tanks. These systems help to prevent excessive vacuum and pressure buildup in the fuel tank. The vent allows any excess buildup to escape through a narrow tube that discharges near the ground.

What is a tank vent valve? ›

Tank vent valves are designed to direct vapors generated during the diurnal cycle. Vent lines from TVVs generally run to carbon canisters. Properly installed, TVVs help protect canisters from liquid fuel.

Does earthing stop static? ›

A key function of equipment earthing is to provide a controlled method to prevent the build up of static electricity, thus reducing the risk of electrical discharge in potentially hazardous environments.

What is bonding in tanker? ›

Grounding and bonding consists of connecting a tank from which a flammable liquid or gas is being discharged to the receiving tank and also to the earth so that any static build up can dissipate into the earth without causing a spark. Transportation.

Do tanks need to be grounded? ›

Most facilities that handle flammable liquids and gases require that transport tanks are properly grounded and bonded to reduce the risk of fire or explosion when emptying or filling these tanks.

What temp does #2 diesel fuel gel? ›

When diesel users talk about gelling, this is the issue they're referring to. Gelling starts to occur at a specific temperature known as the cloud point, coined after the white haze — or “cloud” — that appears as paraffin wax crystalizes. No. 2 diesel fuel has a cloud point of 14 degrees Fahrenheit.

How do you vent a boat fuel tank? ›

A typical vent line will run sideways across the top of the tank until it reaches the hull side and then angle upward to the vent fitting. The hose should run as straight as possible at this point in a manner that allows any fuel to drain back into the tank via gravity.

Which is a risk of a clogged fuel vent? ›

The fuel tank may build excessive pressure due to a blocked vent. This could cause fuel to spray on occupants or bystanders when opening the fuel cap, potentially causing injury. Additionally, if an ignition source was present, this could create a risk of fire, causing injury and/or damage to property.

What is a day tank for diesel generator? ›

A day-tank functions as the immediate fuel source, receiving fuel from a larger fuel storage tank. It can be a stand-alone tank mounted in proximity to the generator, or it could be a sub-base tank with provisions to be used as a day-tank.

How cold is too cold for a diesel engine? ›

Myth #2: Diesel engines won't start in the winter.

“Today's technologies for cold-start are very effective,” Ciatti said. ​“Modern diesel engines start in cold weather with very little effort.” The problem is that diesel jells at low temperatures. Below about 40°F, certain hydrocarbons in diesel turn gelatinous.

Will diesel 911 prevent gelling? ›

Diesel 911 does not prevent fuel gelling – use Diesel Fuel Supplement +Cetane Boost (in the white bottle) as a preventive measure to keep fuel from gelling. Diesel 911 and Diesel Fuel Supplement +Cetane Boost are compatible in diesel fuel and may be used at the same time.

Will gelled diesel thaw? ›

While gelled fuel sounds bad, the good news is that diesel fuel will return to normal as soon as the temperature goes back up above the gel point. Pushing a vehicle into a garage and leaving it for a few hours is typically all that is required to fix the gelling problem.

How does a boat fuel tank vent work? ›

When refueling rapidly or overfilling your fuel tanks, boats vent air that is often mixed with fuel. During refueling, gas goes into the tank and displaces air. The air escapes out through your boat's fuel tank vent.

How do you check a boat fuel tank vent? ›

fuel tank and vent testing - YouTube

Should the vent on a boat gas tank be open or closed? ›

It needs to be open when operating your motor. During storage, the vent must be kept closed to prevent evaporation and loss of your fuel as well as to prevent dangerous fumes from escaping, which could cause an explosion. This is especially true if your tank is stored in a locker or holding box.

Why does the gas pump keep stopping when my tank isn't full? ›

So Why Does It Keep Shutting Off? The shutoff mechanism is primarily designed to shut off the fuel pump when your gas tank is full. It shuts off the fuel supply in this situation because it would be a fire hazard if your vehicle's gas tank overflowed and spilled all over the ground, and the person holding the nozzle.

Why does my gas tank stop filling when it's not full? ›

Basically, the gas is coming out of the gas pump at a pressure that is too fast for the car to take in. If the air vapors do not get out fast enough and the tube gets covered by gasoline, a vacuum forms inside the nozzle which will automatically switch off the flow of gas into your tank.

What causes vacuum in tank? ›

The most common cause of vacuum in tanks is caused by steam (water vapor). When you fill a tank with water vapor, most of the air is pushed out of the tank. As the water vapor cools, it condenses into liquid water. Now you have a little bit of liquid in the tank instead of a large amount of water vapor.

How long is diesel good for in a generator? ›

Diesel fuel in a fuel tank can last the life of the generator – 30 to 40 years. It really depends on the maintenance that is kept on the generator in the fuel tank. It's that ongoing maintenance that will answer the question “is my stored diesel ready for an emergency”.

How long is diesel good for? ›

Under ideal conditions, diesel fuel can be stored between six and twelve months. To extend the life past twelve months, even under the best conditions, it needs to be treated with fuel stabilizers and biocides.

How Long Can diesel fuel be stored? ›

The ideal conditions for storing diesel fuel include keeping fuel dry and at a cool temperature (below 70 degrees Fahrenheit). Such conditions ensure storage life between six to twelve months. To extend fuel life beyond twelve months, fuel stabilizers are required.


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