Just found today after a few days of chasing information to help acquaintance with tractor fuel sediment. This large one should provide several hours of protection for his lift pump. He flushed his fuel tank with a water spray nozzle then flushed with diesel. Found about a quart of sand, grit, and about a dozen paper towels previous owners had placed inside.

Baldwin BF7850 2" X 8" with 5/16 and 3/8 molded hose connection. We plan to dremel off the 5/16" extension.


Price varies from about $8 to more than $30.

I bypassed the little prefilter on my E300D about 50,000 miles ago with a larger metal prefilter. Will probably install one of these larger ones in it's place since sediment should be visible for a few years before it yellows too much.

Here's a photo of it:



Is your fuel that contaminated where you are that this larger thing is really required?

Steve

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Steve A
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I am puzzled by this part which is the 125 microns.

The primary filter (the plastic one by the Fuel Supply/Lift Pump) is nominal 20 microns. And the secondary filter the spin-on one is a nominal 10 microns.

125 nominal microns would be poor filtration.

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84 300D, 82 Volvo 244Gl Diesel

As I understand it:

The pre-filter is primarily to protect the lift pump from larger particles.

I believe most engines with lift pumps have a 'large particle' filter ( or should have one ) before their lift pump. Quite often it is a sock/screen in the fuel tank. The external one is an additional safeguard.

The pre-filter typically is not pressurized and is not rated to withstand pressure.

I believe a 20 micron pre-filter ( if small in size ) would plug up fairly quickly and impede fuel flow.

Last week while searching for a better pre-filter for my friend, I found NAPA and other parts houses typically don't care about microns and tend to sell filters with a low micron rating to be placed before the lift pump. This is wrong and would lead to fuel flow problems and the resulting low power or worse consequences. The prefilters should typically be a screen and not be cellulose or other low micron material.

This previous post says the old style 'L' shape pref-ilter is much larger than 20 microns:

Fuel Filter Micron Rating

That thread also says the WIX pre-filter is 20 micron plus a lot of other google hits says it is 20 micron.

Wix site says it is 140 micron:

https://www.wixfilters.com/Lookup/Exactmatch.aspx?PartNo=33006

I know there are typically no problems with fuel supply while using the Mercedes specified prefilter but I like to have a larger filter since they are plentiful and low cost and would catch more crud before impeding fuel flow.

I plan to replace the metal pre-filter I installed about 30,000 miles ago with the long clear plastic filter & also to try to "stand it up" so water would tend to settle towards the bottom and not pass on to the final filter. Plus the water and crud would be visible while the filter is clear. Just another safeguard in case a service station pumped a little water with their diesel.

The black fuel line is Gates 'barricade' 3/8". It fits over the snipped off Mercedes clear plastic fuel line that was going to the lift pump. Also bypassed the fuel heater since we live in a mild winter state.

Attached Thumbnails

   

Keep an eye on these larger filters as some of them do not like hot fuel and can balloon up, they are good but they do not take heat like the correct pre filters.
Also mount them where they will not be subject to being pulled about either by engine rocking or fuel hose weighing on them.
A lot of people over here in the UK use them on vegetable oil systems and do experience these problems.

I have had my Mercedes since 2007 and even with the one tank full of bad fuel I have had I have never had the plastic (primary filter) plug up. If you are getting bad fuel or something is growing inside of your fuel tank you need to take care of that.

People have put between the Plastic Filter and the Fuel Tank another filter, usually a water separator that has a changeable element. If I had a 125 micron filter that is where I would put it.

I run the stock plastic primary filter (nominal 20 microns) and either a CAT 2 micron of similar Baldwin Filter in the modified Fuel Filter Housing with zero issues.

Filters are supposed to be change x amount of miles bit I don't do that. I wait till I have had some loss of performance of if the mood strikes me to change filters. However, I buy fuel at known places that have good fuel. I buy where the Big Rig Drivers buy.

If a Big Rig Driver gets a load of bad fuel he is on the Radio telling everyone he can to not buy from that station. That costs the Station big bucks. Hence those stations monitor the fuel quality.

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84 300D, 82 Volvo 244Gl Diesel

Note that may similar looking plastic or other see through filters are made for gasoline engines. Those may or may not be compatible with Diesel Fuel and Diesel Fuel Additives.

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84 300D, 82 Volvo 244Gl Diesel

Do you have any actual evidence that the primary filter functions at a 20 micron nominal level? Just based on a visual observation of the screen, it doesn't look like it could be anywhere near that fine. (20 microns is slightly smaller than .0008 inch, which is about 1/4 the thickness of a typical sheet of paper.)

Texasgeezer showed you a link which shows the corresponding Wix filter at 140 microns. What do you have to support your 20 micron claim?

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I read it someplace. Was a long time ago. There is some thread some where where I posted it at the time I found out and where I got the info from. Maybe I am wrong.
There is a decided visual difference between the nylon mesh filters and the ones with the paper element inside.

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84 300D, 82 Volvo 244Gl Diesel

When you look at the fitlers with a screen inside maybe this will give you some ideal.
20 micrions
"It's about one-fifth as tall as a sheet of Paper
In other words, 20 microns is 0.2 times the height of a sheet of Paper, and the height of a sheet of Paper is 5 times that amount.
(for US Letter, a.k.a. ANSI A; 215.9mm by 279.4mm (8.5 in x 11 in); 20lb)
A single sheet of 20 lb, 8.5 inch x 11 inch paper is just 100 microns thick. This style of paper weighs a mere 5 g per sheet."

"It's about one-fifth as wide as a Strand of Hair
In other words, 20 microns is 0.2 times the width of a Strand of Hair, and the width of a Strand of Hair is 5 times that amount.
(average)
A strand of human hair averages 99 µm (micrometers), with blond hair being the finest and black hair the thickest. On a healthy scalp, each strand of hair will last up to 6 years."

https://www.themeasureofthings.com/results.php?comp=height&unit=mc&amt=20&sort=pr&p=1

Another issue is a 20 micron nominal rating means that it will filter out 50% of 20 micron particles. That also means 50% of the 20 micron particles pass through it.

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84 300D, 82 Volvo 244Gl Diesel

Generally, any filter placed before the pump inlet has to have a large micron rating. The reason is that a fine filter would lower pressure in the inlet, which can cause the fuel to vaporize. This is called vapor lock in gasoline cars I'm not sure it ever gets that bad in a diesel, but if you hear somebody complaining about bubbles in the fuel, it may not be air. This is why fuel injected cars often have the pump inside the tank. Some Mercedes have the pump below the level of the tank, all the way at the rear of the car. This keeps the inlet run short and uses the weight of the fuel to keep it pressurized. A high micron rating doesn't hurt because pumps are generally insensitive to small stuff.

If you place the fine filter after the pump, fuel passing through the filter is pressurized, which will prevent vaporization. And son of a gun, that's exactly what Mercedes did. Now you know why.