Why do you have to change your motor oil on a regular basis?

Motor  oil  breaks  down  over time. When it breaks down, it loses  its effectiveness and can no longer properly protect your engine.

In  addition  to  lubricating  an  engine's  moving   parts, motor  oil  is designed to carry combustion by-products  away from the pistons  and cylinders. It is designed to deal with the small  amounts  of water  that form  as  the  engine  heats and cools, and to collect the dirt and  dust that  enter  the engine through the air-intake system. It  also  handles acids that  are  formed  by  the  reaction  between  water  and other contaminants. Sometimes  there  are even  fuel leaks (fuel dilution) or coolant leaks that get into the oil system.

As  a  car  is   driven,  the  level  of   contamination  in  the motor  oil constantly increases. The oil filter removes particles as the oil  passes through the filter, but over time an oil's additives are used up and  the oil itself can start to degrade (oxidize or thicken). At that point, t

Is a "straight weight" oil synonymous with a non-detergent oil?

Not  necessarily.  "Straight weight"  refers  to  an  oil's  viscosity, and usually   indicates  an   absence  of  viscosity  index improvers.  "Non-detergent" refers to the absence of  detergent additives that are used to handle combustion by-products.

What role does viscosity play in a motor oil?

Engineers  work  to  establish an  optimal viscosity for an oil, based on load  and  speed  conditions. They  balance lighter – or low-viscosity – oil, which  provides  little resistance to motion thereby saving fuel  and efficiently transferring horsepower, with a heavier – or high-viscosity – oil that resists being squeezed out of the contact area  between  metal surfaces.

The  complicating  factor  is  that  the  viscosity  of  an  oil varies with changes in temperature – thinner when hot, thicker when cold.  At low temperatures,  we  need  the motor oil to flow readily (not thicken too much or gel). At  high temperatures,  we  need the motor oil to  keep from   becoming   too   thin   and   allowing   metal-to-metal   contact. Therefore, engineers developed multigrade motor oils.

What does viscosity mean?

Viscosity is a measure of a fluid's resistance to flow. A fluid  with low viscosity flows easily and is often called "thin." Water is an example of a fluid with a relatively low viscosity. A fluid with high viscosity is often described  as  "thick."  Maple  syrup  is  an example of a  fluid  with a relatively high viscosity.

My car emits smoke when I start up. What does the smoke indicate?

If the cloud is relatively  blue or  blue/black, it may indicate that oil is being burned along with the fuel. The  possible cause  may be either worn piston rings or an oil viscosity that is too low.

If the cloud is black, it indicates that excess fuel is being burned.

If the cloud is white, it may simply be the moisture  in the cold engine and exhaust system being burned off. If there's a lot of  white  smoke and it continues for a long time, you may  have  an  internal  coolant leak.

What is the API service category classification   system?

Engine  oils  are  currently   classified  by  a two-letter code. Gasoline engine  oil  categories  start  with  the  letter S (originally designated "Spark Ignition" engine oils, we now associate the S with "Service"). Diesel   engine  oil   categories   start   with  the  letter   C (originally designated "Compression Ignition" engine oils, we now associate the C with "Commercial").

The  second  letter  is  simply  a  sequential  designation of improving quality levels over time. In other words, when a new  industry quality level  is  established,  the  next  letter of the  alphabet is used (so SJ replaces SH). The  letters  "I" and  "K"  were purposefully skipped to eliminate potential confusion with other commonly used designations.

What does a viscosity index number mean?

The viscosity  index (VI) number  is  a  measure of the relative change in viscosity of oil over a temperature range. The  HIGHER  the viscosity index, the SMALLER the viscosity change  over  temperature. The VI is not related to the actual viscosity or SAE viscosity, but is a measure of the rate of viscosity change.

The  VI  number  is  typically  used  only  as  an  indicator. The  actual performance  results  of  low-temperature pumpability tests and high-temperature  wear  tests  of  a motor oil are better predictors of good performance in an engine.

Generally,  multigrade   oils (0W-40, 10W-30, etc.) will have high viscosity  indexes.  Monograde  oils (SAE 30, 40, etc.) will have lower viscosity indexes.

What causes my vehicle's oil warning light to go on?

Your oil warning light can come on for a number of reasons including: Low oil level, a failing oil pump, a faulty oil-pressure sensor, blockage in the oil system, excessive foaming of the oil and more. In all  cases, you  should  shut down  your  engine as quickly as it is safe to do so. Continuing to operate your engine with low oil pressure can result in serious engine damage.

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