Changing Freightliner Fuel Water Separator Filters: Step-By-Step Guide

Changing the fuel water separator filter on a Freightliner truck is a maintenance task that should be performed regularly. However, it can be a challenging process, as some people have reported issues with draining the filter and preventing fuel from siphoning out. In this guide, we will walk you through the steps to successfully change the fuel water separator filter on your Freightliner, including tips and tricks to overcome common challenges.

Drain the fuel filter

To drain the fuel filter on a Freightliner, you will need to open the drain plug and wait for the filter to drain. However, it is important to note that this process may result in a significant amount of diesel fuel being released, as some people have reported collecting up to 4 gallons of diesel during the draining process.

If you want to minimise fuel loss during the filter change, there are a few techniques you can try. One method is to pinch the rubber fuel line to stop the flow, which has been suggested by other Freightliner owners. Another option is to install a shut-off valve in the fuel line, which will allow you to control the flow of fuel more easily.

Additionally, you can try to lower the level of diesel in your tank before starting the process, as a full tank can make the filter change more challenging and messy.

• Remove the fuel line from the top of the filter housing. This will require loosening the nut on the fitting.
• Plug the end of the fuel line to prevent fuel from pouring out. You can use a rubber "air tubing cap" that fits inside the line to achieve this.
• Open the petcock at the bottom of the Water/Fuel separator to drain the filter.
• Clean the inside of the sight glass at the bottom of the old filter. Scrub out any crud and rust debris that has accumulated.
• Reattach the fuel line to the filter housing by snugging down the nut and ensuring that the brass ferrule is seated properly in the fitting.
• Cycle the ignition a few times to fill the new filter with fuel using the fuel pump.
• Crank the engine a few times until it starts. You may need to repeat this step a few times to work out any air bubbles in the fuel line.

By following these steps, you can effectively drain and replace the fuel filter on your Freightliner while minimising fuel loss during the process.

Remove the fuel line

To remove the fuel line, you will need to identify which line is the fuel line and which is the fuel pump line. The fuel line will lead to the tank, while the fuel pump line leads to the fuel pump. Once you have identified the correct line, you can proceed to remove it.

First, loosen the nut on the top of the housing with a wrench. A 3/4 open-end wrench may be too small, so you may need to use a medium-sized crescent wrench. Be careful not to crush the fuel line and cause further problems. Twist the nut with the wrench until it can be loosened by hand, then finish backing it off.

At this point, you should be able to see the compression fitting, which consists of a brass ferule around the fuel line that fits into the fitting on the filter housing. The brass nut should be snugged against the ferule to create a tight seal. There may also be a small bushing inside the fuel line to prevent it from being crushed when tightening the brass nut.

Gently tug and wiggle the line to free it from the fitting on the filter housing. Once the line is removed, plug the end of the fuel line to prevent fuel from leaking out. You can use a rubber "air tubing cap" or a similar item that fits inside the line.

By following these steps, you can safely and effectively remove the fuel line when changing the fuel water separator filter on your Freightliner.

Clean the sight glass

To clean the sight glass of your Freightliner fuel water separator filter, you'll need to remove the line from the fuel tank that connects to the top of the filter housing. First, identify the correct line—one line goes to the tank, and the other to the fuel pump. The nut on the top of the housing should be accessible with a wrench.

Once you've located the correct line, use a wrench to loosen the nut. In the experience of one user, this was surprisingly easy to do. A few turns with the wrench, and they were able to finish backing the nut off by hand.

With the nut removed, you'll be able to see the fitting, which is a compression fitting. A brass ferrule around the fuel line fits into the fitting on top of the filter housing. The brass nut snugs against the ferrule to seal it tight. There is also a small bushing inside the fuel line to prevent the end from getting crushed when tightening the brass nut.

After removing the fuel line, plug the end with a rubber "air tubing cap" to prevent fuel from pouring out. These caps are available in various sizes and resemble rubber bullets with the centre drilled out. Select one that fits inside the line and plug the end as soon as you pull the line off.

Now you can remove the sight glass and clean it out. It may take some effort to scrub it clean, but it will be worth it to ensure your fuel system is free of contaminants.

Remove the old filter

To remove the old filter, first, locate the fuel water separator filter in your Freightliner. It is usually found near the fuel tank or fuel pump. Before removing the old filter, it is important to relieve the pressure in the fuel system. This can be done by removing the fuel fill cap or opening the drain plug to release some of the fuel and reduce pressure.

Once the pressure is relieved, place a container under the filter to catch any fuel that may spill. Identify the fuel line connected to the top of the filter housing and loosen the nut holding it in place using a wrench. Be cautious, as fuel may still spill out. To prevent this, you can use an "air tubing cap" or a similar rubber plug that fits inside the fuel line to stop the flow of fuel.

With the fuel line plugged, you can now remove the old filter. Clean the inside of the filter housing, removing any debris or residue. You may need to use a screwdriver and a rubber mallet to create leverage and loosen the old filter if it is too tight. Be careful not to damage any nearby components.

Once the old filter is removed, make sure to clean and inspect the housing for any signs of damage or wear. It is important to ensure that the housing is free of debris and rust before installing the new filter.

Install the new filter

Now that you have removed the old filter, it is time to install the new one.

Firstly, you will need to clean the inside of the sight glass. This can be done by scrubbing out any remaining gunk and rust debris. Make sure to clean it thoroughly and ensure it is completely dry before reattaching it to the new filter.

Next, take your new filter and attach the two new gaskets that come with it. One gasket is thicker than the other, so place the thicker one on top of the new filter, and the thinner one inside the lip of the sight glass.

Now, you can attach the new filter to the engine. Ensure that the sight glass is securely attached to the bottom of the new filter before tightening it into place.

Once the new filter is securely attached, you can reattach the fuel line to the top of the filter housing. Use a wrench to tighten the nut, being careful not to over-tighten it. Check that the brass ferule is seated well inside the fitting before snugging down the nut.

Finally, you will need to fill the new filter with fuel. To do this, cycle the ignition key 4-5 times to allow the fuel pump to fill the filter. You may need to repeat this process a few times to ensure that all air bubbles are removed from the fuel line.

Now, you can try starting the engine. It may take a few attempts to start as you work out any remaining air bubbles in the fuel line. Once it starts, let it run for a few minutes and rev the throttle a few times to ensure that it is running smoothly.

You have now successfully installed your new fuel water separator filter!

Frequently asked questions