Good Gas to Go

The lowly fuel tester is the cheapest thing you'll ever buy for your airplane. Jeppesen makes the best; improve it by stealing the float ball from the AirTrans.

The cheapest flight insurance around comes not from your friendly underwriter-shopping broker but in the form of a little plastic cup that most owners take for granted.

With prices from $4.95 to $15.95, fuel testers don’t get much thought. Just root around for whatever is stuffed into the seat pocket, drain a slug of gas and get on your way.

Nonetheless, a couple of companies have taken a new look at the lowly fuel tester and none too soon, now that owners of new Cessna 172s are confronted with 13 sumps to drain and many airports have begun to frown on the practice of dumping gas on the ramp. It chews up the asphalt and, over time, leads to soil and water contamination. Although the average fuel sample represents only about two cents worth of avgas, returning clean fuel to the tanks will save enough to buy a new fuel tester every couple of years or so, not to mention doing the right thing environmentally.

If there’s such a thing as a standard fuel tester, its the 6-inch-tall clear plastic cylinder that could pass for a cigar tube were it not for the screwdriver tip mounted on the end. We tried a basic model available for $4.95 from Sportys and found it competent, if not inspiring.

A reversible probe allows the tester to be used on both flush mount drains and the Curtis-style petcock drains used on Pipers and some older Beech aircraft. It samples about one ounce of fuel and/or water at a time, which most pilots pour on the ground. If water is discovered, it may take many stabs with that spindly probe to clear the contamination.

While this fuel tester is simple and cheap, it does have three drawbacks. With a diameter of only 1 inch, its easy to splash fuel on your hand if its a windy day or if the cylinder isn’t precisely straight up and down. In addition, the narrow barrel of fuel takes on only a slightly bluish cast when testing 100LL.

More than one pilot has filled the tester, held it up to the blue sky to look at it, and concluded it was filled with uncontaminated avgas when in fact it was pure water.

Last, the yellow plastic probe, while flexible enough to insert into sump opening, occasionally flexs too much and the base of the probe gets jammed cockeyed in top of the cylinder. Once the probe breaks, the tester is junk.

ASA Fuel Testing Cup
One solution to splashback is to make the cup wider. ASAs Fuel Testing Cup is a simple clear plastic cup that, at 1 3/4 inches in diameter, presents a bigger target to downward dribbling avgas. It also means the sample will have a darker hue of blue for 100LL, green for 100 and red for 80 octane fuel.

The cup is made of robust plastic with a stainless steel probe for flush mount drains. It cant be adapted for petcock-style drains. We tested it on a 1997 Skyhawk and a 1978 Mooney and found it easier to use on the Cessna. The stainless probe is rather long and has a tendency to flex if the cup isn’t held perfectly plumb. That was much easier to do while standing under a high wing than when squatting under the Mooneys wing.

In addition, the probe had worked its way loose after draining only three samples. That makes us wary of how long it would remain in service. While it could be glued or re-anchored somehow, for five bucks most people wont bother.

What it did do we’ll was show the color of the fuel. The short, 2-inch-tall cup also made it easy to dump uncontaminated fuel back into the Mooneys tank, but we doubt many Cessna drivers will take the trouble to climb on the wing to save an ounce and a half of fuel.

Jeppesen Fuel Tester
One of the most trusted names in aviation weighs in with a product that provides an interesting solution to the problem of spilled or blowing fuel.

The Jeppesen aircraft fuel tester, at $12.95, is similar to the cigar-shaped benchmark from Sportys, but with some interesting design elements added. The most obvious is a removable collar that slides over the neck, giving fuel a target more than 2 inches in diameter. When not in use, the collar hooks onto the side of the cylinder, allowing for easier storage.

Another refinement is found in the flush mount/petcock adapter. Instead of a simple plastic probe wedged into the neck of the tester, Jeppesen opted for a bronze rod that runs the length of the tester. An internal plastic centering bracket near the top prevents the rod from flexing in use and also allows it to be easily removed for use on a petcock.

Jeppesen also designed a thicker cylinder, which the company bills as a magnified viewing area. Try as we might, we couldnt see a practical difference between it and a standard tester without the magnification. The tester we tried did have one bug that suggested someone was asleep in the quality control department. The reversible screwdriver bit was virtually impossible to insert because of a flaw in the plastic tip.

After much effort, we succeeded in getting the Phillips head inserted (the slotted head was usable), but it took a manly tug on a pair of pliers to get the bit out again.

Retailers and mail order houses will generally make good on an exchange-as were sure Jeppesen would-but who wants the hassle with a $13 item? If you can buy it retail in a pilot shop, try out the screwdriver bit on the spot before purchasing.

Airtrans Fuel Tester
The $11.95 Airtrans Fuel Tester represents yet another variation on the basic theme. Trapped in the cylinder is a yellow float with a specific gravity higher than avgas but lower than either water or jet fuel.

If the ball stays on the bottom, its either stuck or the tester is filled with avgas or automotive gas. If its in suspension, the avgas sample is contaminated with other fuels. If its on top of a clearly defined layer, the sample includes water, jet fuel or other liquids. The specific gravity float relieves the pilot of some of the burden of checking for water in the fuel, but some still may be present in the form of bubbles. Of course, checking fuel samples means more than just checking for water. If you fixate on the floating ball, you might miss debris floating in the fuel.

Quality of construction is average, in our view. The actuator for flush mount drains is plastic and probably more susceptible to the bends than the Jeppesen tester. Fit and finish is roughly the same as the basic model and inferior overall to Jeppesens, in our view.

The GATS Jar is the most complicated of the fuel testers and certainly represents a high-tech answer to a low-tech problem. It was the only fuel tester to come with a four-page instruction manual. (Yeah, we know; this is going a little overboard.)

The $15.95 tester has a number of parts. The jar is a rather standard 12 or 14-ounce plastic jar, roughly the size and shape of something you might find in your pantry. The lid is the heart of the product. A reversible sump actuator snaps loosely into place on one edge of the lid and works with either type of drain. Its flanked by two large holes.

Most of the lid is made of 250-micron mesh that filters water and debris and allows the fuel to be returned to the tanks. In order for the mesh to work correctly, it must be wetted with fuel before any water touches it. It also has to be cleaned before the fuel is dumped back into the tank, or else debris filtered out when the fuel was going into the tester will ride along when the fuel is poured out of the tester.

If used properly, water will remain inside the jar after the fuel is returned to the tank. In addition, the user can detect jet fuel in minute quantities by observing the evaporation of fuel from the screen. If it sounds complicated, it is. It took several tries to get the thing to work as advertised, and by that time we were prone on the ground in order to get samples from the Mooney.

With the learning curve past, the GATS jar works quite well, in our opinion. But testing fuel consumed more time than the rest of the preflight items combined. This tester also needs to be kept in a plastic bag to protect the screen from contamination while its riding in the back of the airplane.

A good fuel tester needs four basic talents: It should be stone simple to use; collect cleanly even under windy conditions; it must clearly show water or other contamination and, ideally, allow you the option of returning fuel to the tanks.

Each of the products we tested fell short of this ideal, making the best choice the one that offers the best compromise. Because even the most expensive ones are by far the cheapest thing your airplane needs, cost really isn’t much a factor here.

The GATS Jar meets three of the criteria, but you pay for it with a product thats tedious to use. The testers by Jeppesen, Airtrans and ASA each fill the need better than the basic model, but have different strengths and weaknesses.

Overall, if we were buying just one, wed pick the Jeppesen because its clean, sturdy and promises years of no-hassle use (as long as you get one that passed quality control).

An even better solution would be to buy both the Jeppesen and the Airtrans. Slip the collar of the Jepp tester onto the Airtrans-it fits, we tried it-and use it until the plastic probe breaks. Then scavenge the little ball from the Airtrans and pop it into the Jeppesen tester.

Or maybe one of the manufacturers will just take care of that for us in the near future by stealing the other guys good idea.

Also With This Article
Click here to view “Sussing Out Alcohol.”

-by Ken Ibold
Ken Ibold is a freelance writer and aircraft owner. He lives in Florida.