install a fuel-water separator

Diesel engines are finicky eaters. At the slightest hint of fuel-borne water, air or contaminants, their spirits droop, leaving drivers with less performance and lower fuel mileage.

Obviously, the best way to prevent such disappointment is by purifying fuel as much as possible before it’s shot into a cylinder. Standard original equipment filters do a fair job of getting rid of dirt and other particulate matter, but they usually won’t snag water droplets, fuel’s leading noncombustible substance. They also do nothing for air bubbles, which are an equally big problem, according to Brad Ekstam, national sales manager for Diesel Products, maker of the Fuel Preporator.

Ekstam got involved with fuel-air issues about 10 years ago, when his dad, a trucker, was having a series of low-power problems with a truck he’d just bought. Repeated trips to an engine distributor’s shop uncovered nothing, but the mechanics strongly suspected a small air leak.

While trying to determine how air might get into his fuel system, the senior Ekstam noticed that diesel fuel generated considerable foam when shaken, as it is going down the road. He then started designing a filtering device that would draw fuel out of the tanks, screen out any air bubbles and send it to the injection pump under a light positive pressure (as opposed to a vacuum, which is the norm). This effort resulted in the Fuel Preporator, which has been on the market for about five years.

Diesel Products has been selling the systems mainly to owner-operators. Lately, though, the company has attracted interest from the mining industry, the Missouri Department of Transportation and Nashville’s largest school bus fleet.

In addition to its air-removal capabilities, the Fuel Preporator also features an extended-life filter and a water separator. An optional fuel heater is available, too.

One of the oldest and best-known manufacturers in the water-separator business is Davco Technology, a company that started in 1975 and is now part of the Penske empire. Unlike some of its competitors, Davco has traditionally sold its products to large fleets.

“We have about every premier fleet out there,” says Gerald Lonski, a Davco technical manager. “Yellow, Roadway, Ryder, UPS, Ruan, Schneider National, Penske, Rollins – you name it. I’d guess we probably have a million units on trucks by now.”

Lonski says large-fleet managers buy his product because it saves them money. First, because it has a clear dome over the filtering element, the shop personnel know when to change it “and, more importantly, when to leave it alone.” Second, it standardizes fuel filter inventory, no matter how many different engines a fleet is running. The savings from this uniformity can be significant.

“A few years ago, a guy from Schneider told me the company saved more than $100,000 annually by switching to a standard filter for the entire fleet,” he says. “Of course, they were running about 9,000 trucks at the time.”

Owner-operators don’t have such high inventory costs, but Lonski says they can still benefit from Davco’s two main truck products: the Diesel Pro 232 for lighter duty applications or the Fuel Pro 382 for heavy-duty applications. Both units have clear-domed tops, enabling truckers to watch their fuel quality after each fill. Such information can be helpful in deciding which truck stops to patronize – and which stops to avoid.

Davco units are on the option lists of all truck and engine manufacturers. They come with a five-year, 500,000-mile warranty.

The information below applies to a Davco Fuel Pro 382 with 120-volt and coolant-based fuel heating. Shop time ranges from two to four hours.


2. Metal fabrication is sometimes required.

The job

1. Choose the correct unit. Truckers’ needs for fuel heating vary by engine brand and area of operation. The 382 accommodates all with an interchangeable bottom plate that features electrical (12-volt DC or 120-volt AC) or coolant-based heat. Information about recommended heating methods are available from Davco or your engine distributor.

2. Find a mounting space. A fuel-water separator must be mounted so the element is above the full mark on a truck’s fuel tanks. It should also be at least 18 inches away from the turbo or exhaust manifold. In Class 8 installations, most units are hung on the left frame rail, near the fuel pump. This typically requires at least one hole being drilled in the rail web (the vertical surface). Such drilling is safe, as long as it’s done no closer than 1 inch from the top or bottom flanges (the horizontal surfaces). If other components prevent a frame mount, you’ll need to fabricate a bracket to hang the unit on the engine.

3. Remove existing plumbing. Spin off the original primary fuel filter, then disconnect and unbolt the filter head. Next, remove the secondary filter (on engines that have one). Some secondary filter heads have priming pumps. If yours is among these, leave the head in place and seal it up with a spin-on diverter cap. Removing the secondary head won’t affect engine performance, but it might require a little extra work to route new fuel lines between the 382 and fuel pump.

4. Attach the unit. Make sure the bolts you’re using – Grade 8 is preferred – fit snugly inside the bolt holes. In cases where dissimilar metals are being joined, protect the mating surfaces with antiseize compound or a thin homemade gasket. Hoist the unit into position, with clear dome up, while an assistant loosely attaches one of the mounting bolts. Repeat the process on the second mounting bolt, then properly tighten both.

5. Determine coolant routes. The best place to tap into a truck’s coolant system is through one of the threaded holes in the block. These provide direct access to the engine’s water jacket, limiting the length of hoses needed to plumb in the 382. When unused, these holes are sealed with metal plugs, which are removed with either a 1/2- or 3/4-inch ratchet or breaker bar. Be sure to drain the coolant before unscrewing one of these plugs. An easier option is to insert a plastic T or Y into a heater hose, if one is nearby. Just pinch the hose on either side of your intended splice with locking pliers and two small pieces of flat, smooth metal – these to protect the hose surface from damage. Make the cut and install the plastic junction. Coolant can pass through the 382 in either direction. Just make sure the chosen outlet side feeds into the engine’s return flow.

8. The element dome should be filled with clean fuel before you attempt to start the engine.

6. Collect hardware. Measure the lengths for any necessary new fuel lines and have them made at a local auto- or truck-parts store. Make sure you bring along a list of all the fittings, clamps and coolant hoses needed for the job. These parts are not provided in the kit because nearly every application is different.

7. Connect the unit. Apply thread sealant to all threaded fitting ends that aren’t beveled. When installing this (normally brass) hardware, be careful to avoid over-tightening. Route the fuel and water lines and secure them with plastic ties to limit rubbing and chafing. Tighten all clamps and refill your engine’s coolant system if you drained it earlier. Plug the 120-volt electrical cord into the bottom plate, and tighten the metal fitting.

8. Fill unit and start engine. Any fuel poured into the clear dome’s top opening will be filtered before it reaches the engine, but you should still use the cleanest fuel possible, if only to maximize the filter element’s life. Fill the dome with fuel and spin on its plastic cap. Start the engine and run it at a high idle. Look for fuel or water leaks. After a few minutes, the fuel level in the dome will drop near the bottom. That’s normal with a new filter.

9. Revisit the installation. Check all bolts, fittings and clamps after running the truck for a day or so. Inspect the unit during normal maintenance intervals.

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