Alex Chamberlain wrote:
Good point, Dave. For what it's worth, though, my #17 that blew
definitely did so on its own, so to speak---not because of
overheating. The car overheated routinely after the head cracked, but
not before, and once the head was replaced it ran perfectly
again---i.e. the cooling system was NOT the culprit. Pity I don't
have much maintenance history on the car. I don't know exactly when
the original head was replaced, nor when the trap oxidizer recall was
done. If there was an overlap, we could blame the trap for the #17
cracking.
On 11/7/05, Dave M. <[EMAIL PROTECTED]> wrote:
Before condemning the #17+ heads, you need to know the details behind
the failure (re: that SDL with a bunch of cracks in a '17.) Blowing a
radiator hose and driving for an hour with the temp in the red and no
coolant in the system will likely crack a #22 head also.
All heads CAN crack - even old iron heads. I've seen a small number of
OM601 and 602 heads (maybe about as many as OM61x heads) that have
cracked. The cracks look just like cracks in 603 heads - they crack in
the same places (around prechamber and valve ports mostly). They
represent a TINY fraction (<1%) of the number of 601/602 heads produced
(vs maybe 20% of the heads from '86-'87 603 engines). Most crack because
they are abused some way. Aluminum heads expand and contract FAR more in
response to heating/cooling than iron heads and because of that, require
that additional measures be taken to compensate for that activity. There
is evidence that aside from the heat stress of a trap oxidizer plugging
up, SOME of the cracking problem resulted from the design of the head
gaskets used before the the late '80s. Mercedes also redesigned the head
itself - several times. A few certainly cracked because they were flawed
in the manufacturing process. One problem with the introduction of
aluminum heads was that they couldn't be magnafluxed as iron heads could
to reveal flaws. That left pressure testing as about the only practical
method for testing in the field and Mercedes acknowledges in the engine
manual that even heads that pass the pressure test may still be flawed
and fail once installed.
Marshall
--
Marshall Booth (who doesn't respond to unsigned questions)
"der Dieseling Doktor" [EMAIL PROTECTED]
'87 300TD 182Kmi, '84 190D 2.2 229Kmi, '85 190D 2.0 161Kmi, '87 190D 2.5
turbo 237kmi
