Exactly where is/was a 300SDL's trap oxidizer located, and what does
it look like?
After purchasing my SDL two weeks ago, I called service department of
the local Mercedes dealership to ask them to consult the database and
find out whether the car had ever undergone the removal of its trap
oxidizer under recall. Surprisingly, it hadn't. That was strange for
such an old car, I thought, but the service rep said there were still
a few stragglers out there. He also said that the recall had expired
a couple of years previously (news to me), but that the dealership still
I took the car in today to have the work done. When I got it back late
this afternoon, I looked under the hood to see what was different. The
piece that I thought had to have been the trap oxidizer -- a foil-covered
horizontal cylinder about 15 inches long and maybe 3-4 inches in diameter,
oriented fore and aft to the right of the valve cover and at about the
same level -- was still in place.
The only component of the exhaust system that was obviously new was a
length of exhaust pipe well downstream of the turbocharger, the segment
slanting downward aft of the turbo and leveling out underneath the floor-
pan before connecting to the front end of the muffler.
Now as I understand it, the problem with the trap oxidizer is that the
porcelain grid inside the thing might eventually come apart and enter
the hot section of the turbo, causing damage. If that's the case, then
it makes no sense to replace any exhaust-system components *downstream*
of the turbo as part of this recall.
It's also my understanding that this recall involves not just removing
the trap oxidizer and replacing it with either an oxygen catalyst or a
section of straight pipe (I've heard both versions; with my '85 300D, it
was the former), but also removing and inspecting the turbocharger for
damage, and if any is found, replacing the turbo.
The mounting hardware on the turbocharger had obviously not been removed
and replaced; it was still covered with the standard surface corrosion
that's commonly found on older exhaust-system components. The same was
true of the aforementioned cylinder to the right of the valve cover.
The work order reads "Replace oxidizer trap for diesels only. See bulletin
96-1121." Followed by: "Replacement of oxidizing trap for diesels only.
Trap replaced as per bulletin."
But the only parts that are listed on my receipt are as follows:
126-490-13-20 exhaust pipe
603-140-03-03 pipe elbow
202-492-01-81 coupling rin [sic]
126-492-01-82 ring, exhaust
107-492-00-82 damping pad
107-492-00-82 damping pad [listed twice for some reason]
There's nothing in there that would appear to be a replacement for the
trap oxidizer. "Exhaust pipe" has to refer to the long section under-
neath the car.
Is it possible that the dealership didn't bother pulling the trap oxidizer,
but simply installed a new section of exhaust pipe in an easy-to-reach area
so that something new and shiny would be visible in the engine bay to make
it *look like*
they did what I asked them to do?
Before anyone mentions black helicopters or tinfoil beanies, I can come up
with a reason why this might be so: because they recall expired a couple of
years ago, and despite what the service rep said about still honoring it,
the dealership may have felt it wasn't worth their trouble -- especially
if they were no longer going to be reimbursed by DBAG -- and didn't want to
piss off a customer by coming out and saying so.
'91 300D 2.5
"Am I crazy, or is it hot in here?" -- Charles Manson