Introduction: Installing a Secondary Fuel Filter (diesel)

About: I do a well many things, but not many things well.

For my first Instructable, I'll document the steps I took to install a secondary fuel filter in my 1983 Mercedes 240d. Currently I'm running a mixture of WVO and biodiesel. My fear is that I'll be on the road and have to do roadside maintenance because of a clogged filter- now I don't have that problem.

*Please note- if you try this, you do so at you own (and car's) risk.

Step 1: Tools and Materials

razor blade, or knife
protective gloves
something to catch the fuel that spills


Fuel filter- I used a Mann WK 842/3
***3/16" fuel line 4-5 ft***
In line fuel shut-off switch
(x2) 3/16 T-connections
zip ties


Hose clamps
-small: enough for all hose connections
-Large: To attach to optional mounting bracket
custom mounting bracket (not discussed in this instructable)

***If you're running WVO or biodiesel, you will want to get synthetic lins such as Viton or A1 grade Marine fuel line.***

Step 2: Diagram

Here is a rough diagram of how I installed the filter.

Step 3: New Filter Placement

Later on I'm going to build a bracket for the filter and mount it in the engine compartment. For now I'm just going to use zip ties to keep it in place.

So find the location that you want the filter to go. This will give you an idea as to how much hose to cut. (I did not do any measuring here and depending on where you place the filter, your measurements will be different.)

Step 4: Cut Your Hose

My old hose was in bad shape, so I did not even think about re using it.

You'll need to cut 7 pieces

Here they are:

1. Fuel pump to T-connector(1)
2. T-connector(1) to 2nd Fuel Filter
3. T-connector(1) to Shut-off switch
4. Shut-off switch to Orig. Filter
5. 2nd Fuel Filter to T-connector(2)
6. T-connector(2) to Orig. Filter
7. T-connector(2) to engine

Cut your hose with the razor blade and fit them to the secondary filter*

*Note. The filter connections are much bigger then 3/16" so they are really hard to put on. When I re-mount my filter I'm going to use a larger hose and 2 reducing couplers.

Step 5: Assembly

Assemble the components so that it looks like the picture in the last step. Remember that your lengths might be different.

Also note that there are arrows on the filter. Make sure you put it on the right way!

Step 6: Remove Old Hose Pt. 1

I started by removing the hose from the fuel pump to the filter, and replaced it with my set up. The image shows you where the hose goes.

Step 7: Remove Old Hose Pt.2

Remove and install the hose going from the Orig. filter to the engine. Here's another 2 images.

Step 8: Prime the Filter

Almost done!

Now that everything is hooked up, you're just about done.

First, loosen, or take out the bolt on top of the new filter.
2nd, unscrew the hand pump and pump it until fuel comes out the top of the filter screw hole (It took about 25 pumps for me).

Remember to re-screw you hand pump back down and then tighten up the filter bolt.

Clean up and you're done!

Step 9: How It Works

Now you are done. So here is how it works.

Keep the switch in the 'OFF' position. You'll be filtering your fuel through the new filter. When it gets clogged, just turn the switch and the fuel will go through the original filter so you won't have to spend a lot of time doing roadside repairs.

If you have any tweaks, let me know.