We have a 1987 300SDL, that just turned over 250K over the holiday
weekend..As far as I know, the engine has never had major overhaul but when
we bought it our mechanic said it looked like the timing chain tensioner was
new as it had this shiny knob thing sticking out on the pass side of the
front of the engine..The car runs flawlessly and uses very little oil but
this weekend we went to north Texas and it was a bit chilly (28 degreesF)
and both mornings, we started the car and it fired right up and ran
good..But within about 45 seconds the engine started making a noise I can
best describe as what an AC compressor sounds like when it's going
out..Sorta made a grumbling, rattling sound..I raised the hood and it
sounded like it was coming from the valvetrain area..Soon it stopped and
didn't reappear till the next morning..But now we are home and it's not that
cold it didn't do it..Could the timing chain tensioner be hanging up or
something? I have a note into my mechanic but I think he is still out of
Thanks in advance!!! John
I have an '84 300TD. I have heard similar noises (Loud, senseless racket)
that turned out to be failed mounting bushings on the air cleaner housing.
At slow idle it was the worst and it would vanish at 100 rpm faster than
that. The noise is impressive; probably the loudest noise coming from under
the hood. I could also describe it as shaking a paint can with a handful of
rocks in it. Maybe the lower temperatures changed the idle speed just enough
to set up the harmonic rattling. It was at its worst when the engine is
idling slowly enough that is visibly shaking from side to side. Next time
just lean on the air cleaner housing with some authority and see if the
noise changes. Or you can lift up on the air cleaner housing. If it raises
more than the slightest fraction of an inch, it's the bushings.
Thanks for the reply...It's definately coming from the front of the engine,
but so far has not done it again..The six cylinder diesel engine doesn't
have the problem with the air cleaner bracket you describe, as it's remotely
mounted on the inner fender..I do know what you mean tho, had a 300SD that
did that and I had to replace the bracket...Had one guy mention the vacuum
pump and I do believe it to be original..Somewhere I read an article that
these engines are notorious for failing vacuum pumps and I right away talked
to our mechanic about it and he said he had never experienced one fail on
this engine..Been going to take the car out to him but won't do much good if
it won't re appear...Maybe when it gets really cold here..
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