I use Castrol GTX in 20W50 grade. However, thicker does
not automatically mean better -- like it used to. This is
a topic of due consideration. I have researched oils and how
(and why)they work and would enjoy jumping in the mix.
Given the engines in our LBCs, 20W50 is probably best.
Multi-viscosity oils obviously have properties unlike single
viscosity oil -- which isn't really just one viscosity! Oil,
like many liquids, thins or becomes less viscous as temperature
increases. And what is the right viscosity for a COLD engine
is different from the needs of a HOT engine. Leaving out
specific temperatures (because I can't remember them), 20W50
oil has the viscosity of cold 20 weight oil -- when cold and hot
50 weight oil -- when hot. That is, it is thinner than 50
weight when cold for better circulation when cold and thicker
than 20 weight oil when hot for better thin film tear strength.
But what do all these words mean?
Short answer: Use 20W50 in your LBCs
Long answer: The meaning of 20 and 50 are given above. The
" W " is/was for "winter." 20W50 weight multi-viscosity oils
are made by adding coil-shaped polymers to pure lighter weight
weight oil. The polymer coils unwind as they are heated and
cause an apparent thickening of the oil. This increased
viscosity improves the tear strength of the thin film covering
the bearings and preventing metal-to-metal contact. Thicker
oil also doesn't flow through narrow spaces as quickly helping
to keep oil pressure higher with worn bearings <with excessive
clearance>. This is of course, is a double edged sword as one
of oil's main uses is to cool the bearings by flowing the hear
away in the oil. Thicker oil cannot carry the heat away as
quickly. So what is the logical answer?
(1) Shoot Rick. He's on one of his techno-posts. or
(2) for a healthy engine, use a multi-viscosity oil with as
small a viscosity range as possible. Why? Because, although
the polymers thicken the oil they provide NO LUBRICATION and
in fact, their addition dilutes the lubricating properties of
I like being a physicist.
> I've used a number of different brands of 20W50 in my MGs, and
> I swear some are thicker than others. I just tried Pennzoil
> and it seems the thinest. Quaker State gets my vote for the
> thickest. This is based on my totally subjective impression of
> pouring rate, oil consumption and pressure reading on the gauge.
> I just wondered if anyone else has noticed a difference.
> BTW: Does anyone have an opinion on which brand is best?
> Bob Donahue (Still stuck in the '50s)
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