David Brodbeck wrote:
Peter Frederick wrote:
Speaking of pressure vs flow, I remember hearing that in the 70's, Alfa
Romeo had big warnings in their owner's manuals about not exceeding
2000 rpm until the oil pressure came down off the peg at idle -- seems
that oil in those days was viscous enough at low temperature that there
was essentially no flow to the cams until the engine warmed up, and if
you ran the revs up to 6000 cold the cam lobes wore off pretty
fast.....
Even my '89 VW Cabriolet has a note in the owner's manual to avoid high
RPM until the oil temperature is over 50 C, which corresponds to the
bottom peg on the oil temperature gauge. I seem to recall hearing that
some cars had a three-state temperature light that would light up blue
at cold temperatures to remind you to take it easy, but I can't recall
which ones.
Sometimes I wonder just how high the oil pressure in a Mercedes gets
after a cold start. The gauges only go up to 3, of course, so we can't
really know. My Cabriolet has a 5 bar pressure gauge and it usually
pegs out on cold starts. I'm sure a Mercedes does even better.
As long as the pressure is 3 bar or greater, the engine is protected
using approved oil in the viscosity that is appropriate for the temps.
Using almost any group IV synthetic oil (even Mobil 1 15W-50) and your
better off in cold weather than using even an 0W-20 or 5W-20 weight
conventional oil. At high temps, the group IV oils also offer greatly
improved safety.
The over pressure valve on the oil filter and the oil pump open (thus
limiting pressure) at around 6-7 bar!
Marshall
--
Marshall Booth Ph.D.
Ass't Prof. (ret.)
Univ of Pittsburgh School of Medicine
[EMAIL PROTECTED]
