I owned a 1980 300D a while back and I remember the oil pressure indicated
at idle around "1.5". The engine was in need of an overhaul. Had excessive
oil consumption as well as blow by.
A worn diesel engine for a 300SDL should indicate a below "3" on the
My question is : a rebuilt engine (20,000 miles) should indicate a "3" on
idle, right? That should be a sign of "health" for a rebuilt engine.
No. Normal oil pressure is 3 bars (guage) when driving, and at least half a bar
at idle. Whether the actual reading hot, idling, is half a bar, one or two bars
has more to do with oil grade and age than engine wear.
425 White Horse Pike
Diesels' idling oil pressure is typically 1.5 to 1.75 BAR (22 to 26 psi)
when hot and 3.0 BAR on the gauge when cold or when being driven. The
actual upper limit is about 85 psi and that's regulated by the oil
pump's pressure relief valve. Worn engines will have somewhat lower oil
pressure at hot idle. No engine will have 3.0 BAR oil pressure at hot idle.
My '81 240d that I got a couple of years ago has 3 bar at all times. Gauge goes
to 3 at startup and never goes down until I turn off engine. The engine has
alot of blowby, shuts down in under 3 secs. after blocking valve cover hose,
yet it starts right up in the coldest of weather,no block heater. Maybe once or
twice during the hottest days of summer did I see the oil gauge drop half a bar
from 3. Does this indicate a bad pressure relief valve?
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