On Tue, 30 Apr 1996, Robert Rhodes wrote:
> Answer: Investing in fully synthetic oil for your Minor would
> waste money and could even do more harm than good. Older engines have
> larger bearing clearances and oil pumps with lower rates of delivery than
> modern ones; thus they generally need a thicker oil to maintain optimum
> pressure. Synthetic oils have be designed to cope with modern engine
> developements such as turbochargers, with highly stressed bearings
> working in extreme temperatures. A top grade synthetic, with its high
> lubricating efficiency, would even prolong the running-in of your newly
> rebuilt engine.
> Many oil companies have introduced or reintroduced 'classic' oils
> recently..."
>
> So he thinks that 'classic' oils are the way to go. Any
> engineers or mechanics out there have another opinion on the clearances
> and oil pump theory? What oil pressure have those who have switched to
> synthetics seen?
Ummm..... I have a hard time with this explanation. If you're working
with a good synthetic that is the same viscosity rating as was originally
specified, then film strength and viscosity (hence oil pressure and
lubrication) should be at least as high as with the dino oil.
I don't have any LBC experience with synthetic oil yet, but I have a '74
BMW with something in the neighborhood of 200-250K miles (maybe 50-100K on
a DPO's half-assed rebuild). To make a long story short, when I changed
from the DPO's 20W50 of unknown brand to Mobil 1 15W50, the hot oil
pressure stayed the same, the cold oil pressure improved (went down), and
the engine got (and stayed) cleaner. Although this is not an LBC, this
particular engine seems to me to be a bit on the loose side, so it's
probably a similar situation.
The case that Mr. Lots-of-stuff-after-his-name mentions, I believe, is an
A-Series engine, right? It is my impression that Mobil 1 is a pretty
popular oil for people who race this particular engine. At the least,
Vizard feels that it is not a bad choice. I'll be reporting, at the time
of my next oil change, on what happens when I switch to synthetic in my
freshly rebuilt A-Series.
The one caveat I have repeatedly heard is that the claim that synthetic
oils are good for 25-30K miles (with 3000-5000 mile filter changes) is
dubious on a modern engine, and really not applicable to older engines.
Although the oil will not break down from combustion by-products in that
time as natural oils would, the little bits of crud that are too small to
get filtered out will accumulate in the oil. The result can be increased
wear.
Hope this helps-
Michael Chaffee
mchaffee@ux1.cso.uiuc.edu
CCSO's secretary has officially disavowed any knowledge of my actions.
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