jury is NOT out on the
use of multi-viscosity oils for racing;
it�s just that some people are not yet up
to speed on the benefits of new technology
crankcase lubricants for racing applications.
Some still adhere to the �straight grade�
oils that can do the job in some situations
but also leave something to be desired.
is probably a good time to explain what
the oil viscosity numbers mean and how they
can relate to the real world of racing.
Viscosity is a measure of oil�s ability
to flow through a certain size orifice at
a designated temperature. Let�s use typical
SAE 20W/50 oil as an example as to what
the numbers mean. The viscosity grade number
of this oil (20W/50) can be divided into
two parts; �20W� and �50.�
The first part (20W) means that 100 milliliters
of oil must flow through a certain size
orifice within a given amount of time at
The test temperature varies with the viscosity
grade, but all are at or below 32�
The �50� part of the viscosity grade number
means that the oil must flow through a certain
size orifice within a given amount of time
all viscosity grades from 20 to 60. As the
grade numbers get higher, the oil is thicker
and flows at a slower rate.
summarize this, multi-viscosity means the
oil meets two viscosity requirements, one
at a low temperature depending on the first
number of the viscosity grade, and a second
the second number in the viscosity grade.
What all of this means is that an SAE 20W/50
oil flows like an SAE 50 oil at 212�
and flows like an SAE 20W oil at 14�
This provides the best of both worlds; good
lubricant flow at low temperatures to get
to the critical areas quickly, and adequate
film thickness to protect those same critical
areas at high temperatures because the oil
does not �thin-out.�
take a look at straight grade oil used in
a racing engine and see if there are any
undesirable conditions that develop. A good
example of this is the racer that uses a
straight grade SAE 50 oil, then heats it
F with a heating
blanket around the dry sump tank or has
a heating element in the tank. The engine
is cold and is fired up for qualifying and
run one lap to warm up and one lap for time.
But what happens to that 212�
oil when it
hits that 70�
cast iron block?
You can bet pole money that it cools down
significantly and gets thicker. Cool (thick)
oil does not flow as freely as hot oil,
so the pump may max out on pressure and
start to bypass. Why heat oil up only to
have it cool down? When it cools down after
hitting the cold cast iron and the pressure
increases to the point of bypassing, power
is wasted pumping and bypassing thick oil
when that power could have been more effectively
used at the rear wheels. Bypassing oil at
the pump also reduces oil flow to the bearings.
SAE 20W/50 oil were used in place of the
SAE 50, flow characteristics would be like
an SAE 20W oil at the low temperatures and
like SAE 50 oil at higher temperatures.
If the 20W/50 hits the cold cast iron block
and drops to 100�
like the SAE 50. It will still flow well
because it has thin oil characteristics
at low temperatures. The bypass will probably
not be opened and the oil pumped is all
going to lubricate engine parts.
same benefits exist with other multi-viscosity
oils like SAE 10W/30 or SAE 10W/40. One
thing to be aware of with lower viscosity
oils (especially 10W/30 or thinner) is that
the oil film thickness (the ability to lubricate
bearings and to carry load) is less then
a 20W/50 and on some engines may not protect
as well as higher viscosity oil. This can
be due to a number of variables that include
engine speed, horsepower output, bearing
clearances, oil system efficiency, and oil
item to watch for on the label of the container
is �Energy Conserving.� This information
is found on the label inside the API doughnut
that also indicates the API service designation
and the viscosity grade. In the lower part
of the doughnut will be the words �Energy
Conserving� which means the oil improves
fuel economy in a standard test by reducing
internal engine friction in a passenger
car engine. In a race engine, this relates
to increased horsepower.
of the Winston Cup teams use 10W/30 for
qualifying then switch to 20W/50 for the
race. On restrictor plate engines that develop
about 430 horsepower, some of the teams
use SAE 10W/30 or 10W/40 Motor Oil at Daytona
and Talladega. Frequently, 10W/40 is used
in unrestricted engines early or late in
the season when the weather is cold.
summary, the use of multi-viscosity oils
in racing applications is advantageous.
Reliability is improved since the oil flows
well when it is cold and gets to critical
areas quickly. It also protects the engine
well under high speed, high output, and
high temperature conditions.
of this information applies to gasoline
racing engines only. Racing engines that
use methanol or nitromethane fuel is another
Your Nearest Distributor, call 1-800-345-0076.