Which 30 Weight Oil Do I Use? 0W-30, 5W-30 or 10W-30?
TSO ASL XLT
We get asked this question so often that we have included this special page dedicated exclusively
to answering the question.
AMSOIL 0W-30, 5W-30 and 10W-30 synthetic motor oils are ALL 30 weight oils. The answer is that ANY one can
be used regardless if your vehicle owners manual says to use, for example, a 5W-30. "W" means winter. In winter
weather the 0W oil will flow like a 0W oil, and the 5W will flow like a 5W oil and a 10W will flow like a 10W oil
just until the engine warms up. In order to understand the differences one has to first understand that the
numerical values given to these various weight oils are strictly empirical numbers. For example, 0W does not
mean that the oil has no weight. That is one of the reasons why we say it is strictly an empirical number.
In order to determine the differences between the three oils one has to look at the kinematics viscosity of each
lubricant. The kinematics viscosity is essentially the amount of time, in centistokes, that it takes for a
specified volume of the lubricant to flow through a fixed diameter orifice at a given temperature.
Let's compare the kinematics viscosity of the three AMSOIL lubricants:
AMSOIL 0W-30 is 57.3 cST @ 40 deg. C, & 11.3 cST @ 100 deg. C
AMSOIL 5W-30 is 59.5 cST @ 40 deg. C, & 11.7 cST @ 100 deg. C
AMSOIL 10W-30 is 66.1 cST @ 40 deg. C, & 11.7 cST @ 100 deg. C.
As you can see from the data above the kinematic viscosities are extremely close. Therefore, whether you use the
0W-30, 5W-30 or the 10W-30 is strictly a matter of choice. With the small differences in kinematic viscosity you
would be hard-pressed to detect these differences on initial engine start-up without specialized engine test
All three oils are excellent motor oils and ANY one can be used in a vehicle which
requires either a 0W-30, 5W-30 or 10W-30 oil as well as in several other engine applications including an engine
which recommends a 5W- 20 oil.
AMSOIL Series 2000 0W-30 Severe Service motor oil is one of the best synthetic lubricants AMSOIL manufacturers for
gasoline engine passenger vehicles and light trucks. The molecular and chemical technology used to develop this oil
was derived from AMSOIL's Racing Oil. It is a 35,000 mile/2-year motor oil. This is the same oil used by numerous
police vehicles and severe duty fleets nationwide. In fact, many national racing teams use the 0W-30 for the
qualifying event, then they change to the AMSOIL 20W-50 Racing Oil for the race. The extra horsepower and friction
reduction from the 0W-30 often assists a race driver in attaining a better starting position. In fact, we know
exactly which race teams use it, but cannot disclose that information.
This leads to the next topic: many people also ask us if the 0W-30 is too thin a viscosity oil for high ambient
temperature operation. The answer is absolutely not! Thicker viscosity oils are not always necessarily better
since in addition to its' various engine lubrication functions, an oil must also effectively transfer heat. Only
about 60% of an engines cooling is performed by the engine coolant, and only on the upper half of the engine. The
remaining 40% of an engines cooling is performed mainly by the engine oil.
Although a vehicle that is recommended to use a 30 weight oil can also use a 40 weight oil, it is usually not
needed. You will gain absolutely no benefit from using a thicker viscosity oil if it is not needed. The only time
we recommend a 40 weight oil, such as AMSOIL's 10W-40, to a customer in a passenger car or light truck application
is if the vehicle's engine is excessively worn and consumes oil at a higher than normal rate or if the vehicle is
being used for very severe duty, high load, high temperature applications.
We hope this brief discussion has answered your questions. If we have not sufficiently answered your questions or
if you would like an additional explanation or recommendation for your specific application please email us using
the link at the bottom of this page.
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