Additives are not needed. Exhaust smoke is unburned fuel, although these
old engines will smoke some during acceleration they should otherwise be
relatively smoke free, especially as the sulfur is removed from the fuel.
Excess smoke can be due to low compression (unadjusted valves or low
compression due to ring wear), a mis adjusted injection pump or just a
dirty air filter element that restricts the air flow into the engine.
Sound to me like the ALDA may need adjusting (assuming the valves are
Before doing anything, check that the pressure line from the exhaust
manifold to the firewall mounted safety switch and on to the ALDA are
clear - This line has a banjo filter at the manifold that often plugs up.
You should not need any fuel additives and only smoke you should get, is whn
first starting up and if you floor it from the traffic lights!
Adjusting valves is about 1 to 1.5 hr job for an equipped garage. For a DIY
first time, it would take a bit longer. You need a set of offset wrenches
plus one that will fit the power steering pulley nut in order to turn the
engine over. You also need a set of feeler gauges. Istead of repeating what
has already been written, try a google search - here is the result of one
for Google Groups:
You could get a garage to do it for you, but make sure they do it with the
engine cold and that they use the proper clearances.
Make sure you ionstall a new valve cover gasket and make sure it is
properly seated (It's a bit of a trick to get the cover back on without
dislodging the gasket.
Adjusting the ALDA is a job that many garages either don't know about or
won't do. It is very simple, but there is a small risk that you might damage
the ALDA. Again, instead of repeating the method, here is the result of a
Google Groups search:
Cleaning the banjo fitting and the pressure tube from the manifold plus the
ALDA adjustment can do wonders for a sluggish 300D. Also, make sure none of
the ruber connectors on the pressure tube are leaking - the ones on the
firewall switch sometimes crack.
If those links don't work try your own search.
If you want to get into working on your own MB, there are a few MB mailing
lists that could be helpful if you join.
Have others noticed that diesel fuel now smokes a lot less than a few
years ago? I used to get heavy soot on the left rear trunk lid emblem
on my 300SD. Now, while there is still some, it's greatly reduced.
I'm assuming this is from the introduction of cleaner burning fuel.
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