Picture of Installing a Secondary Fuel Filter (diesel)
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.
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Step 1: Tools and materials

Picture of 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

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

Step 3: New Filter Placement

Picture of 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.)
Monkeyboy134 years ago
Dude! I have that same car!
ronorr5 years ago
Very Important. The filter in the parts list is a WK842/2 but the filter in the photograph is a WK842/3. They are rather different. You want a WK842/3 NOT a WK842/2
skree (author)  ronorr5 years ago
Ronorr, Thanks- I've changed it to the correct filter.
skree (author) 6 years ago
alex: Yes, unless it is clogged then the fuel will go through the origional. Linux- correct alex- senthetic lines are the way to go- but I'm under the hood enough to watch 'em. Plus, this will work for regular diesel as well. gog- I mention that as optional. The fuel is under low pressure and they were not orignally, so again- I'll keep an eye out. BTW, I keep a couple of feet of fuel line along with a lot of tools in the trunk- just in case. Thanks for the comments!
Derin skree6 years ago
also,diesels feed fuel via gravity
skree (author)  skree6 years ago
I've added the synthetic line info and use of hose clamps to the parts/tools step. I guess that I should have been more clear. Thanks.
Sandisk1duo6 years ago
That's cool, but wouldn't fuel still flow through the secondary filter even if the switch is "on"? Yay biodeisel, just filter the fuel BEFORE putting it in your tank
I think they use the 2nd one and have the original as a backup
oh, now i see the creator should change his fuel lines to synthetic ones, Biodiesel (the home-made type) will eat away at your tubes until nothing else is left!
gog6 years ago
I'd recommend some hose clamps on those fuel lines so they cant pop off.