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Which 30 Weight Oil Do I Use, 0W-30, 5W-30 or 10W-30?

AMSOIL 5W-30 100% Synthetic Motor Oil (ASL)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 of the vehicle owners manual recommendation. To better understand, in a 5W-30 oil, the "W" stands for winter performance. 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. This multi-grade performance allows faster oil flow during cold start, however when the oil warms up, they all reach the designated 30 weight viscosity.

Video reference: Synthetic Oil Basics

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 kinematic viscosity of each lubricant. The kinematic viscosity is essentially the amount of time, in centistokes, that it takes for a specified volume of lubricant to flow through a fixed diameter orifice at a given temperature.

Let's compare the kinematic viscosity of the three AMSOIL lubricants

AMSOIL 0W30 is 57.3 cST @ 40 °C, & 11.3 cST @ 100 °C AMSOIL 5W30 is 59.5 cST @ 40 °C, & 11.7 cST @ 100 °C AMSOIL 10W30 is 66.1 cST @ 40 °C, & 11.7 cST @ 100 °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 equipment.

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.

Signature Series 0W30 100% Synthetic Motor Oil (SSO) Severe Service motor oilAMSOIL Signature Series 0W30 100% Synthetic Motor Oil (SSO) 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/1-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.

Click here to see the TYPICAL PACKAGE that most people use for oil in their cars for their daily drivers when they switch to Amsoil for the first time.

When you look at the different Amsoil products, you'll see category descriptions next to them. (Look to the right of the 10W40 bottle in this example and you will see a list starting out with the letters API.) This will help you determine which oil is compatible with your engine.

API Service Category for Gasoline Engines

Category Description Status
SN The API SN category is an improvement over the API SM. API SN was introduced October 2010, designed to provide improved high temperature deposit protection for pistons, more stringent sludge control, and seal compatibility. API SN with Resource Conserving matches ILSAC GF-5 by combining API SN performance with improved fuel economy, turbocharger protection, emission control system compatibility, and protection of engines operating on ethanol-containing fuels up to E85. Current
SM For 2010 and older automotive engines. API SM was first introduced 30 November 2004 for gasoline engines. Category SM oils are designed to provide improved oxidation resistance, improved deposit protection, better wear protection, and better low-temperature performance over the life of the oil. Some SM oils may also meet the latest ILSAC specification and/or qualify as Energy Conserving. They may be used where API Service Category SJ and SL earlier categories are recommended. Current
SL For 2004 and older automotive engines. API SL was first introduced July 1, 2001 for gasoline engines. Oils meeting API SL requirements have been tested according to the American Chemistry Council (ACC) Product Approval Code of Practice and may utilize the API Base Oil Interchange and Viscosity Grade Engine Testing Guidelines. They may be used where API Service Category SJ and earlier categories are recommended. Current
SJ For 2001 and older gasoline engines. API SJ was first mandated in 1997. SJ spec oil can be used where API SH and earlier categories are recommended. Current
SH For 1996 and older engines. Valid when preceded by current C categories. Obsolete
SG For 1993 and older engines. Obsolete
SF For 1988 and older engines. Obsolete
SE For 1979 and older engines. Obsolete
SD For 1971 and older engines. Obsolete
SC For 1967 and older engines. Obsolete
SB For older engines. Use only when specifically recommended by the manufacturer. Obsolete
SA For older engines; no performance requirement. Use only when specifically recommended by the manufacturer. Obsolete

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