A few easy ones, I hope. ('79 300TD fuel filters and hatch)

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Tom Plunket - 23 Nov 2006 18:55 GMT

I would like to change the fuel filters in my car. The translucent one
has recently turned black (I'm sure in part due to the 5 gallons of
virgin soybean oil I poured into the tank), so I figure that's as good
an indication as any. When I got the car a few weeks ago, it was the
color of cedar. The new filters I got from Autohaus AZ have a metal
screen in them, and don't look the same as when the one was new on my
car; is the color from the fuel, or are the Autohaus filters something
different/wrong/less desirable? The brand on them is Monark
Diesel/Bosch. (I also have the spin-on Mahle filter, which is branded
as Knecht/Mann and has a Kengst picture on the site, but obviously can't
see through those to judge their filtering capability.)

The real question is, how do I depressurize the system, so I don't get
fuel all over the place? Do people really just wrap this stuff in rags
and spin 'em off (which is as much as a search of this group has
yielded, and no websites have given me much more than, "the fuel system
is under pressure").

I also got a couple of new struts for the hatch, since the hatch won't
stay up by itself. I can see how the hatch attaches (three bolts on
each hinge, or so it seems), but I'm looking for tips on actually
removing it. What do people do? It seems like maybe a four-person job,
one wrenching and three holding it above their heads. ...and when I do
get it off, are the struts bolted inside somewhere? I don't see any
access to the interior bolt, if there is any. (The struts go straight
into the body, along the roofline.)

thanks for any tips,
-tom!

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T.G. Lambach - 23 Nov 2006 21:37 GMT

It's messy, wear latex / vinyl gloves!

The fuel system is under a bit of pressure but that makes more of a mess
than anything else. I'd try to do this work with a near empty fuel tank
so the fuel doesn't flow out while the small filter is being changed.

The issue when opening the fuel system is to get the air out of it
afterward. That's why there's a hand primer pump. It's that 6" high pipe
like device with a black plastic top which unscrews so you can pump it.
There's a rubber sealing ring under the plastic cap that eventually
breaks and the hand primer pump then needs to be replaced ($20) or there
will be seepage and air leaks into the system.

The air needs to be expelled or the motor will crank and crank while it
expels the air. Air compresses so the 2,000 psi injection pressure gets
to compress a lot of air before it's gone. Watch for the bubbles to
disappear from the clear plastic fuel lines while you hand prime,
remember, both filters must be filled with fuel.

Some shops fill the spin on filter with injector cleaner before
installing it. Saves work and priming. Clean fuel is fine too.

Happy Thanksgiving.

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Richard Sexton - 07 Dec 2006 14:24 GMT

A friend of mine put one tank of filterred Chinese restaurant oil
from his neighbor whose been using this stuff for a couple of years
in his 300D.

My friends cat clogged a fuel filter in about a day. He changed it and got
5 more miles down the road. Then it clogged again. 20 filters later...
... it finally ran 5 miles without clogging a filter.

Good way to clean all that crus in your fuel system I suppose.

Monark are the cheap Chinese filters. I've never used them just
the German filters, but I use Monark glow plugs. They don't last as long
as the BOSCH or Beru parts but they burn hotter.

Signature

Need Mercedes parts? http://parts.mbz.org
Richard Sexton | Mercedes stuff: http://mbz.org
1970 280SE, 72 280SE | Home pages: http://rs79.vrx.net
633CSi 250SE/C 300SD | http://aquaria.net http://killi.net

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trader4@optonline.net - 07 Dec 2006 15:51 GMT

Here's a related question. The "spin on" fuel filter is really more of
a bolt on, at least in my 80 300SD. The bolt that goes through the
top of the filter holder has a washer on it under the head. Where do
you get these washers? They don't come with the filters I've bought.
I've managed to reuse them, but new ones would be best to avoid leaks
around the washer at the top.

TIA

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Tom Plunket - 07 Dec 2006 19:23 GMT

> A friend of mine put one tank of filterred Chinese restaurant oil
> from his neighbor whose been using this stuff for a couple of years
> in his 300D.

Yeah, that's the end-goal. ;)

> Good way to clean all that crus in your fuel system I suppose.

Yep.

Now, though, since changing out the filters, I get bubbles coming into
the fuel prefilter. Not just air in it, but bubbles entering it from
the supply line. Any tips on what I should look at for this?

As for the hatch- the struts weren't too hard to replace once I figured
out how to get at them. Dropping the trim panel over the back speakers,
there're a couple of holes in the headliner that /almost/ line up with
the bolts holding the struts to the body, and one of them was set with
permanent loctite which was no fun to get out but I did eventually
triumph. It was sort of tedious to get the pin back in through the
hatch itself, but with enough perseverence and a thin coat of antiseize
and it eventually slid through. The hairiest part was doing the first
one, since the struts wouldn't hold the hatch up and I was constantly
afraid that my prop was going to fall out, crushing my fingers. ...once
I got the first one replaced, though, the hatch did stay up by itself.
With both of them replaced, it actually takes some effort to shut the
hatch, a nice turn although not having the key to the lock means if I
don't slam it hard enough I gotta crawl back into the car, unlock it,
and try again...

Pics of the operation were taken, and I'll get those up on my website
before long along with the story of bypassing the ACC servo.

-tom!

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