Diesel and Water Don't Mix

The wrench is turned over to this position to tighten the filter.

As if it were administering the notorious Chinese water torture, H20 in your fuel system can destroy the interior of your engine, drop by drop.

Changing fuel filters at recommended intervals and servicing water separators as necessary will go a long way toward keeping you moving and preserving your injection system.

Pure diesel fuel that meets viscosity and lubricity standards is good for the injection system and will even preserve it from wear, rust and corrosion. But water that collects at the bottom of a fuel tank will often mix with the fuel and may pass out of your truck’s fuel tank and into the injection system. And since water rusts fuel tanks and lines, it often contains rust particles and other dirt that can enter the fuel system and cause serious trouble.

Water in your fuel can corrode finely machined injector parts. If there’s a high enough water content, it can even completely destroy an injector by blowing off the tip.

To prevent this, truck diesels are equipped with fuel filters capable of removing particles down to a very fine micron level and separating water out. Failure to change your filters can shut you down when debris in the filter blocks the flow. That debris can also mean dirt getting into your injectors.

Changing filters
You can replace primary and secondary filters with factory filters with the same part numbers. You can also take the part numbers to your supplier and may be able to buy similar filters that will replace the OEM ones. Your dealer or distributor can often identify the correct filters of other brands using the OEM part numbers.

Bill Lattemann, a technician at Penn Detroit Diesel Allison, says the most important thing in changing filters is to “avoid losing the prime.” This means keeping the system full of fuel so the truck will start up when you’ve finished.

Just follow the procedure below, and you’ll be able to restart. Remember to keep the primary and secondary filters properly identified via the labels or part numbers used on them.

What You’ll Need
Band-type filter wrench of
appropriate size
Container of clean diesel fuel
Oil can with clean engine oil in it
Bucket or other container to collect fuel that drains out of the system
Clean rags

1. Unpack your primary and secondary filters, and find a place to rest them that will hold them straight up, with the open ends upward. You may be able to use the square boxes they were packed in to do this. Refer to the tightening directions on the filters and note how tight you should make them upon installation (usually 3/4 to 1 full turn). Then fill them almost to the top with clean diesel fuel. Carefully lubricate the filter ring seals with an even layer of clean engine oil.

One of the most important keys to keeping the system full of fuel and ready to start is filling the filters before installing. But make sure to use clean fuel!

2. Shut the engine down. Some systems have a shutoff valve located after the secondary filter. If this system has such a valve, shut it off.

3. Place a bucket under the primary filter. (The primary filter is located between the tank and the fuel pump in the system). Wipe the filter base where the filter connects to it to remove dirt that could later get into the new filter during installation.

4. Install the filter wrench in the correct direction to turn the filter off (counterclockwise as viewed from below). The wrench is installed over the filter body from below, typically by reaching in under the frame rail. It will tighten up and grab the filter as soon as you rotate the handle, if it’s installed in the right direction. Turn the filter with the wrench till it’s loose, then loosen it with your hand till it clears the threads, and remove it. If you have trouble getting the wrench to grab the filter, try carefully wiping any oil or fuel off the filter body and from the inside surface of the wrench.

5. Make sure the filter’s flat ring seal comes off with the filter. If not, remove it from the filter base, as leaving it on will often result in a leak. Then wipe the filter base where the filter fits onto it with a clean rag.

6. Immediately install the new primary fuel filter. Waiting can cause loss of prime. (Removing the secondary filter at this point is even worse!) Check the labeling and make sure you have the primary filter and not the secondary (in some systems, the two have different thread sizes). Then carefully raise the filter into position until the female threads in its center are lined up with and butt up against the male threads on the filter base. Gently rotate the filter, keeping it as vertical as you can, until the threads engage one another.
Note: If the threads start to catch but it quickly becomes hard to turn the filter, don’t force it! It’s cross-threaded. Turn it back off, and try again at a different angle. If it’s perfectly vertical and the mount is also vertical, and you line it up carefully, the threads should engage easily.

7. Turn the filter till the gasket just contacts the filter base (it will suddenly get harder to turn). Then, begin watching how far it rotates as you tighten it farther. Tighten it by hand till it just reaches the recommended range or until you need the wrench. Then, if necessary, reverse the position of the wrench and complete the tightening operation. Since you’ve lubed the gasket, tightening should be easy. Don’t overtighten, as this kind of gasket needs little torque to seal.

8. If the system has one, reopen the shutoff valve. Immediately start the truck and allow it to idle for a minute or two to remove all air from the fuel system.

9. Shut the engine down and, if the system has one, re-close the shutoff valve.

10. Install the secondary filter in exactly the same way as the primary, following Steps 3-7. This is the filter located in the line running from the fuel pump to the cylinder head. Again, make sure the filter is full of fuel and that you don’t wait to install the new filter after removal of the old one.

11. Once the new filter is installed, reopen the shutoff valve (if you have one), start the engine and run it for a couple of minutes, checking for leaks. Leakage will normally occur only on the secondary side. Drain and properly dispose of the used filters and the drained diesel fuel in an environmentally correct and safe manner.

Replacing spin-on filters or filter cartridges at recommended intervals, or as restriction gauges or fuel levels indicate, will keep those expensive injectors happy and keep you rolling down the road.


Position the special wrench as shown to loosen the plastic collar.

Pay Close Attention to the Model’s Specs

Some filters, notably the Racor 400R series, consist of a filter head with priming pump, a spin-on filter element and a re-usable collection bowl at its base. The Racor unit will work under up to 30 psi pressure (depending on the individual model) and can be used on either side of the fuel pump, but separates water more effectively in the primary position. The bowl is spun on and off the new filter cartridge and reused. The cartridge should be replaced every 10,000 miles, if your fuel vacuum gauge reads between six and 10 inches of vacuum, or if you notice a loss in power.

The replacement procedure is basically what has been described above except that you tighten the filter and bowl by hand, not with a wrench. As with all different manufacturers you will need to stay alert for ways that a particular model does things differently. With this Racor, for example, your first step is to loosen the vent plug at the top and open the drain valve, located on the bowl at the bottom, to drain off some fuel. Then re-close just the drain valve. Later, after your new filter is installed, your last step is to make sure the vent plug is still loosened, and then operate the primer pump on top of the filter
mount until fuel comes out of the vent plug. Close the vent plug, start the engine and check for leaks.

The 380 Fuel Processor is also a typical example of the many large units used in the primary position to separate water and filter the fuel. The part number for a new filter cartridge like this one is often marked on the unit’s base. Your dealer or distributor can normally cross the number over so you can get an equivalent filter of another brand if you wish. You can also take the old cartridge to them for identification.

Drain the unit completely (with cap removed) and then remove the large, plastic housing before changing the filter. Make sure to get new O-ring seals for the bottom of the plastic housing and for the plug at the top (they often come together in a kit with the new cartridge), and to clean the grooves before replacing the seals. Before reinstalling the cap, slowly fill the unit with clean fuel until bubbles stop coming up from underneath. Fill to a level about halfway up the filter before installing the cap.

When you re-start your engine after the replacement of this unit’s filter, remember that fuel levels in these filters depend upon resistance to flow through the filter. The level will start out low, but as the cartridge fills with dirt it will rise. Some units have a line that indicates when the level is high enough that the filter should be changed.


Routine Maintenance Will Go a Long Way
Standard, spin-on fuel filters should be replaced at the miles or hours the truck maker recommends, if there is high restriction on the fuel restriction gauge or if you notice a lack of power.

If you have a separator with a clear plastic bowl, inspect the contents daily. Water is heavier than the fuel and will sit on the bottom with an obvious line between the two. Drain the separator as often as necessary to ensure that water never reaches the top of the collection bowl. On most separators, just shut the engine off, and then place a container below the drain. Open the drain and allow the contents to pour into a container placed below.

If the unit has a pump, operate it to keep the separator full during the procedure and speed things up. On units without a pump, drain only long enough to get clean fuel to prevent losing the prime. If water keeps coming, remove only a small amount (a cup or two). If necessary, close the drain valve, start the truck and run it for a few minutes to make sure the system is fully re-primed. Then repeat the process to complete the draining. If draining frequently and using fuel from reputable suppliers, you won’t have to drain excessive amounts.


For further information, contact:

Davco Technology LLC
(Makers of 380,
382 Fuel Processors)
(734) 429-5665
www.DavcoTech.com

Detroit Diesel Corp.
(313) 592-5000
www.detroitdiesel.com

Racor Div. Parker
(209) 521-7860
www.parker.com/racor

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