The Austin Healey Owners Club of NSW ( Sydney Australia) mag. has an article
written by a local oil chemist and from memory he made these points.
Oils may be formulated differently for different markets and countries.
Currently in Australia Castrol oils have 1000ppm of a product based on zinc for
improving mechanical wear properties.
It is important to operate oils at their designed temperature. He quoted
results from tests that wear was greater at 50.C than the designed 80.C.
Interesting he also stated that wear was higher at low revs ( 2000rpm) compared
to 4000rpm.
Also 'diesel' configured oil is not necessarily good for us and that some
companies were reducing the zincs to 800ppm.
When I converted my engine from Castrol R that intoxicating vegetable oil to
mineral oil some years ago I consulted a number of oil company chemists about
the change-over and replacement and they all said the same thing,"just use a
good grade of oil and change it more often"
Remember that oil performs many duties in an internal combustion engine;
.washes down all the crap from cold starts and loose rings.
.carries away all the surplus fuel that isnt burnt.
.cools the piston and other hot bits.
.carries away all the water that enters the engines as humidity overnight when
the bits cool down and water droplets form.
.then in its spare time while circulating for the duties above it provides a
film to seperate the sliding and rotating metal bits.
I always rub the dirty oil and the fresh oil between finger and thumb to feel
difference in the lubricity ( the wear control feature). The colour change from
new to used indicates the amount of crap being washed out of your engine.
Looks dirty then it is dirty and contains fine particles just like a good
quility car polish!!!! Which is slowly but surely removing the relatively soft
materials in the bearings.
Cam followers in Healeys need all the help they can get
Remember the 'relief ' valve is a flow control device and is generally open
allowing oil to bypass-more bypasses at start up when the oil is thick and the
clearances close as temps are low, this makes it hard for cold ,thick oil to
move along all those small drillings and holes. This is when the bypass valve
is at its most open. As temps. rise, the oil thins and the engine clearances
are wider accepting more oil volume.
I wont try to explain it here but there is a precise formula connecting volume,
temperature and pressure.
P(1)xV(1)divided by T(1) equals P(2)xT(2) divided by T(2)
Basically my message is at low temps you wont necessarily get good circulation
even though the pressure reads high.
At high temps you may not maintain pressure because internal flows are too high
and the pump may not provide sufficient volume to hold the pressure up.
Multi-grade Oil viscosity is used to help manage these varing conditions.
Unless you are an expert stick to the manufactures guidelines.
Austin and Healey handbooks always recommended different oil grade and supplier
for different continent/markets
Joe
|