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What You Should Know About Motor Oils & Lubricants

by Larry Carley copyright

motor oil filler cap

Without various oils and lubricants, no vehicle will go very far. The engine needs motor oil to lubricate and cool the bearings, pistons, rings, cylinders and other moving parts.

The motor oil you use should meet the viscosity and service ratings recommended in your vehicle owner's manual. Most engines today are factory-filled with 5W-20 because 5W-20 improves cold starting, fuel economy and allows the oil to reach critical upper valvetrain components in overhead cam engines more quickly than heavier viscosity oils.

Some European cars specify 0W-20 while Toyota specifies 0W-20 for its late model Prius hybrids.

Most vehicle manufacturers also approve 5W-30 and 10W-30 for year-round driving. But heavier grades such as 20W-40, 20W-50, straight 30W, etc. are formulated for higher temperatures and loads, and are too thick for cold weather driving. Using a heavier viscosity oil in a late mode vehicle with variable valve timing may adversely affect the operation of the cam phasers and set a trouble code.

Our advice is to follow the viscosity recommendations in your owners manual.

Types of Motor Oil

What type of motor oil should you use in your engine? The answer to that depends on the type of driving you do, how often you change oil, and how much you want to spend on an oil change.

There are three basic types of motor oil: conventional, synthetic and synthetic blends.

Conventional motor oils are refined from crude oil and treated with additives such as detergents, viscosity improvers, anti-wear agents and corrosion, oxidation and foam inhibitors to improve their performance. Many conventional motors oils today such as 5W-20 actually contain high quality base oils similar to those used in synthetic products. Most (but not all) conventional oils meet basic OEM lubrication requirements, and are fine for everyday driving. However, in our opinion conventional motor oils should not go more than 5,000 to 6,000 miles between oil changes. For longer service intervals (7,500 miles or higher), a synthetic oil is a must.

Conventional oils should NOT be used in applications where special performance and anti-wear additives are required. This includes many late model European cars and SUVs that have special motor oil requirements, as well as late model GM vehicles that specify a motor oil that meets their Dexos standards. Conventional motors are also not the best choice for turbocharged, supercharged or other high output engines. These types of applications require a synthetic motor oil.

Synthetic motor oils are man-made and highly refined to provide the best possible lubrication under the widest range of operating conditions, including extreme temperatures both hot and cold. Synthetic oils can withstand conditions that cause ordinary oils to oxidize and break down. They provide superior high-temperature protection, easier cold-weather starting and reduced friction for better fuel economy.

But synthetics are expensive so Synthetic Blends are also available as a more affordable alternative. A blend obviously can't deliver the full benefits of a 100 percent pure synthetic, but it is a step up from a conventional oil. You can also create your own "blend" by mixing one or more quarts of synthetic oil with conventional oil when refilling your crankcase after changing the oil.


Motor oil has a limited service life inside an engine. Heat oxidizes the oil and breaks down the lubrication qualities of the oil over time. Combustion blowby gases such as soot, unburned fuel vapor and moisture dilute and contaminate the oil. The oil filter only removes microscopic wear particles, dirt and soot, but it can't get rid of moisture or sludge. Anti-wear additives are also depleted over time as are corrosion inhibitors and anti-foaming agents. Eventually the motor oil wears out and must be replaced.

How often should you change your oil? It depends on the type of driving you do, the type of oil in your engine, and environmental factors. Short trip stop-and-go urban driving is much harder on oil than highway driving. Cold weather increases condensation in the crankcase. High heat applications such as those found inside turbocharged or supercharged engines also shortens oil life.

Most auto makers today recommend longer service intervals ranging from 5,000 miles to 7,500 miles to 10,000 or more. Our advice is to follow their recommendations, and make sure you use a motor oil that meets the OEM requirements for your engine.

For short trip stop-and-go driving, especially during cold weather, more frequent oil changes are a good idea to prevent sludge from forming inside your engine. With conventional motor oils, change it every 3,000 miles. With a synthetic blend or full synthetic motor oil, change it every 5,000 miles.

Many auto makers today recommend 7,500 mile oil change intervals, which is okay for newer low mileage vehicles filled with a synthetic or synthetic blend motor oi). But on some applications (notably certain Chrysler and Toyota engines), stretching the oil change interval to 7,500 miles has resulted in engine sluding problems and expensive engine repairs.

For older high mileage vehicles (over 100,000 miles), we would recommend changing the oil every 3,000 miles or 6 months if you do mostly city driving. If you do long distance commuting or mostly highway driving, you can stretch the interval out to 5,000 miles with a conventional motor oil.


Some new vehicles do not even have a recommended service interval for changing the oil and filter. They use an "oil monitor" system to let you know when your oil should be changed.

Most oil monitor systems do not actually test the oil's condition (though some may use a sensor to measure oil conductivity to determine contamination). Most oil monitor systems estimate remaining oil life by tracking hours of engine operation, miles driven, ambient temperatures, time spent idling and other factors that affect oil life. Using algorithms based on laboratory and field testing, the oil reminder system calculates how much oil life has been used and how much is left.

Under ideal operating conditions, the oil change light may not come on for up to 10,000 miles or more on some vehicles, but that is under ideal operating conditions only. Many vehicles operate under "severe service" conditions in regular city traffic. Severe service includes short-trip driving (seven miles or less, especially during cold weather), extended idling, towing a trailer or driving in dusty conditions.

What's more, the oil life monitor estimate is based on using a high quality full synthetic or synthetic blend, not a conventional motor oil that may not go the distance.

Choosing the "Right" Motor Oil for Your Engine

Always follow your vehicle manufacturer's recommendations as to the VISCOSITY and SERVICE RATING required for your engine.

Most late model engines specify viscosity ratings of 0W-20, 5W-20 or 5W-30 for gasoline engines. The required viscosity rating may be marked on the oil filler cap on your engine, or on the dipstick. You can also find it in your Owners Manual. Using the WRONG viscosity oil may cause your Check Engine light to come on. Many engines are very sensitive to the thickness of the oil, especially late model engines that have Variable Valve Timing. Oil that is too thick may slow changes in cam timing that can affect emissions, performance and fuel economy.

All vehicle manufacturers also requires motor oils that meet specific performance standards for the year/make/model application. The American Petroleum Institute (API) and the International Lubricant Standardization and Approval Committee (ILSAC) have various service ratings that motor oils must meet. These ratings are marked on the oil container so make sure the rating matches the one required for your engine.

For the latest API and ILSAC ratings, see API Motor Oil Classifications


A wide variety of aftermarket oil and crankcase additives are available that may provide various benefits for your engine. Most auto makers say crankcase additives should not be necessary as long as the motor oil you use meets their performance requirements. However, for older high mileage vehicles many additives can be quite useful. These include oil additives that reduce oil burning and leakage such as STP, Casite and others. These type of "motor honey" additives can help reduce oil consumption and help quiet noisy valve lifters. Some also contain zinc/phosphorus (ZDDP) and other anti-wear additives to protect older engines with flat tappet camshafts and lifters. There are also additives to reduce friction and wear, and cleaners for removing sludge from the crankcase in neglected engines.


Automatic Transmission Fluid (ATF) is a type of oil formulated for use in automatic transmissions and some power steering systems. ATF contains special friction modifiers, seal conditioners and anti-wear additives required by different types of automatic transmissions. For more information on this subject, see Guide to Automatic Transmission Fluids.

Continuously Variable Transmissions (CVT are another type of transmission that also require a very specific type of ATF.

CAUTION: Different automatic transmissions require different types of ATF. Make sure the ATF you buy is the correct one for your transmission. If you use the wrong fluid, it could cause shift and engagement problems or damage your transmission! If you are not sure what type of ATF to use, refer to your vehicle owners manual or the marking on the transmission dipstick filler cap.


For manual transmissions and differentials, a single 80 or 90 weight gear oil or a multi-viscosity gear oil may be required. But many manual transmissions, transaxles and power steering systems specify ATF for lubrication. Some vehicles that have limited-slip differentials require a special type of oil for the clutch packs.

CV joints require their own type of grease (never ordinary chassis grease), but U-joints can typically operate just fine with chassis grease or multi-purpose grease. Wheel bearings always require a high temperature grease.

Other special lubricants that may be required for certain jobs include: moly-based brake grease for lubricating calipers and shoe pads; silicone brake grease for lubricating caliper and wheel cylinder pistons and seals; white lithium grease for lubricating door hinges, cables and other sliding mechanisms; dielectric grease for lubricating and protecting spark plug boots and electrical connectors; and anti-seize for spark plugs, oxygen sensors and fasteners.

motor oil More Motor Oil & Engine Lubrication Articles:

API Motor Oil Guide 2020

ISLAC GF-6 Motor Oil Specification Update February 2020

New Motor Oil Specifications 2014

What Every Motorist Should Know About Motor Oil

How Often Should You Change Your Oil?

How To Change Your Oil

Oil Filters

Certified Master Technicians Speak Out On Oil Change Intervals

API Motor Oil Classifications

Motor Oil Additives

Motor Oil Viscosity

Synthetic Motor Oil

Troubleshooting Low Oil Pressure

Oil Pump Diagnosis

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