Fuel Filter in vacuum line? - PeachParts Mercedes-Benz Forum

cook · #1 06-11-2005, 09:25 PM

I noticed a link containing a picture of a fuel filter in the vacuum lines leading to the interior stuff and transmission. This is on a 1980s 300D I think.

It said the filter helps keep oil out of the lines.

I'd like to understand this more....

Where would the oil come from? Why?

How does a fuel filter stop the oil?

boneheaddoctor · #2 06-11-2005, 09:36 PM

Its a check valve....it allows flow in one direction only...

cook · #3 06-11-2005, 09:42 PM

Here is the link....

http://207.210.95.34/~boostd/Vacuum/2.jpg

I think I see the check valve, but that other thing sure looks like a plain o' fuel filter.

boneheaddoctor · #4 06-11-2005, 09:50 PM

Quote:

Originally Posted by cook

Here is the link....

http://207.210.95.34/~boostd/Vacuum/2.jpg

I think I see the check valve, but that other thing sure looks like a plain o' fuel filter.

Damned if you aren't right..............

Never saw that before......and no you should NEVER have oil in the vacume lines...you have a shutoff solenoid that has failed if you do.

I can't think of what logic possesed them to do that.

rg2098 · #5 06-11-2005, 09:51 PM

Its there in case the vacuum pump fails and dumps oil in the lines. It can be a very big mess if it happens, but those pumps don't fail frequently. I have heard of people putting them in the shut-off valve line, those will dump oil in the vac lines when they bust as well.

Palangi · #6 06-11-2005, 09:57 PM

That doodad is called a strainer. It's not actually a fuel filter. The part number can be found waaaay back in some obscure thread several years ago. Its purpose is to give a visual indication of oil in the vacuum system.

cook · #7 06-11-2005, 09:57 PM

Wouldn't oil flow (very slowly) through a fuel filter?

Maybe the filter buys you a little time to keep oil out of the rest of the system?

sokoloff · #8 06-11-2005, 11:30 PM

It's a pretty common item on our diesels. Lots of folks use them. I have two on my 240D. It gives you a quick visual check to know that the vacuum lines are clear. Will alert you to oil or ATF in the vacuum system before it gets into everyting includiing the passenger compartment. Good idea and cheap insurance I think.

Len

JimmyL · #9 06-12-2005, 12:04 AM

My '85 wagon came with one.

mespe · #10 06-12-2005, 08:03 AM

I pump WVO through into my fuel tank. I can pump up to 100 gallons of
WVO through the filter before it starts to collapse.

hockeynut · #11 06-12-2005, 10:10 AM

I agree with Sokoloff - they are there simply as a visual check for a torn vacuum shutoff valve diaphram. Will alert you to any oil before it becomes a big mess. I put a new one inline after I did a bunch of vacuum line work and replaced the shutoff valve. Funny thing is the PO had one in as well, but it was all full of oil

I've had it in for several months now - no vac leaks and it is clear as can be.

Palangi · #12 06-12-2005, 07:55 PM

I kinda cheated. I just replaced a couple of the short hunks of rubber vacuum hose with clear vinyl tubing. So far so good.

cook · #13 06-12-2005, 09:02 PM

All the info sure is good, but I still have lingering questions.

Is it just a plain ol' fuel filter?

And its main purpose is to allow you to see in the lines to be sure there is no oil in them, right?

So the filter part serves no purpose? Or does the filter part maybe give you a surface so you can see discoloration and know that oil has been in the line?

Also, which direction should the filter be installed..... Should the vacuum flow in the same direction as the fuel would flow, or in the opposit direction?

Palangi · #14 06-12-2005, 09:17 PM

I would think it would not be an ordinary fuel filter. It has to pass air (vacuum actually) with very little restriction. There is a specific MB part number for it. As I recall, there are supposed to be two of them at specific locations, and they are directional. I believe the part number can be found in an ancient thread but you would have to search pretty deep for it. Maybe somebody who has one can read the part number off of it.

Also, there was a writeup on this in an ancient Star Magazine. Maybe somebody still has it around.

dmorrison · #15 06-12-2005, 10:12 PM

The filter is only put in the vacuum line to allow you to see if any components, vacuum pump, shutoff valve or tranny, are leaking into the system. If so and IF you check it on a regular basis you can repair the one unit leaking before it ruins the entire vacuum system.

I have 2 in my cars. one in the main vacuum hose sub units and the other from the shutoff valve to the ignition switch.

I am using the fram in line furl filter. any filter will work. for a while I had lawn mower in line CLEAR filters. worked very nice.

The fram filter.

http://www.acehardwareoutlet.com/productaddonsdetails.asp?id=85326&source=froogle

it works very well.

The dealer used to sell a clear in line filter for this I have not seen it lately at the dealer. Besides the Fram filter is only 2-3 bucks/

Dave

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