I've got a '74 240D (I know, I know - but I like it!) that consumes oil it
appears only at highway speeds (70 mph - yes, it does go that fast).
My mechanic believes the problem to be the Injection Pump Diaphragm. His
reasoning behind this is when we removed the Air Cleaner snorkel at the
Intake Manifold, there was engine oil present in it. Not much, but enough
to recognize it. There was a bit more oil than usual in the Air Cleaner
assembly as well. Franz's (his real name) theory is that the Injection Pump
Diaphragm is weak, allowing engine oil to pass through it and enter the
engine's Intake System. The car does NOT take off on it's own (remember the
late 70's Diesel Rabbits?), and does not run alone on this extracted engine
Another anomaly is that after a hour or so long highway run, the engine will
produce pre-ignition sounds (sort of like spark knock) at around-town
speeds, averaging 30 - 45 mph. Franz's theory on this is that the
pre-ignition is being caused by the trace amount of engine oil being sucked
in through the Intake Manifold and burned. This usually goes on until the
following day when magically, no more pre-ignition sounds once the engine is
warmed up. Speaking of which, according to the temp. gauge, the engine
sticks right at 175 degrees once it's at operating temperature.
A replacement of the Injection Pump Diaphragm was completed, with disastrous
results. LOTS of smoke, and horrible engine performance. Different shims
were even tried; but to no avail. The original Diaphragm was re-installed,
and all was once again as it were in my little Diesel-World. Franz's only
other recommendation was to have the Injection Pump rebuilt, or purchase a
rebuilt unit as a whole, with injectors as well.
The engine itself really runs like a top - even with the anemic performance
on the four-speed Auto Trans, it puts along just fine for me. A bit loud on
the Freeway, but not as loud as my '66 912!
My question is would anyone agree with the Injection Pump Diaphragm theory?
Thanks in advance for the assistance, everyone -