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Pdf-fb on overheated engine heart-wrong oil

Posted 04-20-2011 at 07:42 AM by

Biological Resources Engineering FACTS
Understanding Engine Oil Labels
David S. Ross
Extension Agricultural Engineer
University of Maryland System
Selecting an engine oil can be very confusing. Labels have bright colors and catchy phrases to describe the oils within. How do you decide which oil is best for your car, truck, tractor or piece of machinery? Or, how can you be sure you are buying oil that meets the specifications in your owner's manual? A brief overview of engine oil chemistry, selection and advertising will follow so you will understand some important things about oils. However, the most important information on the oil label are the American Petroleum Institute (API) Classifications and Society of Automotive Engineers (SAE) viscosity numbers.

Engine Oil Chemistry
Every engine oil on the market is a mixture of a base oil and numerous additives. The base oil can be mineral oil, refined from petroleum crude oil or synthetic oil produced chemically. There are hundreds of additives and they are not easy to categorize. Just note that every quality engine oil has an additive package that enhances its quality to perform in your engine.

Selecting an Engine Oil
Consult your owner's or operator's manual to find the recommended oil for your engine. The manual will specify both API Service Classifications and SAE viscosity numbers. It is important to know what these terms mean:

The American Petroleum Institute (API) Service Classifications are based on two engine service groups and a quality rating. The current API Service Classifications have been in use since 1972. For engines manufactured before 1972 the owner's or operator's manual will designate an oil according to an older API system. Consult an equipment dealer if there is a question about which classification of oil to use.

A typical API Service Classification found on a can or bottle is SG-CE. (See Figure 1.) The first letter of each of these pairs (S and C) denote the engine service group. API recognizes two engine service groups: the S series and the C series. The "S" stands for spark ignition - engines fueled by gasoline, alcohol, natural gas or propane. The "C" stands for compression ignition - oil fueled (diesel) engines.

The second letter of the pair denotes the quality rating. At this time a high quality rating for an oil is designated by the letter F or G. New quality ratings are assigned as better classes of oils are developed and tested. Generally, the new higher quality oils can be used where lower ratings were specified for older engines.

The engine service group and the quality rating are combined to give the API service classification such as SG or CE. The SG means it is for a spark ignition engine and has a quality rating of G. The CE means the oil is for a compression ignition engine and has a quality rating of E. A given oil may satisfy both engine service groups and have an API service classification of SG-CE, for example. Currently, SG (spark ignition, G quality rating) and CE (compression ignition, E quality rating) are the top engine oils in their respective categories.

The Society of Automotive Engineers (SAE) has established a scale which indicates oil thickness (viscosity). SAE numbers include, for example, 10W-30, 5W-40 and sometimes just a single number such as 5W, 10W, 20, 30, 40 or 50. The "W" next to a number means the oil thickness was measured at a very cold temperature, as low as -35 degrees F, when the oil is thickest. A number without a W suffix indicates the oil thickness was measured when the oil was hot (210 degrees F).

Two numbers separated by a hyphen indicate a multiviscosity oil. Multiviscosity oils are tested at both hot and cold temperatures and are recommended for all-season use. Multiviscosity oils are able to lubricate moving parts over a wide range of temperatures. These oils contain a viscosity index improver or polymers to change the viscosity of the oil as temperature changes. A multiviscosity oil such as a 10W-40 will function like an SAE 10W oil at cold temperatures and like an SAE 40 oil when the temperatures are warm or hot. Note that a multiviscosity oil can not be made by combining individual SAE oil viscosities together. Multiviscosity oils require the addition of polymers in order to gain the ability to function differently at different temperatures. Equipment operator's and service manuals specify which oil viscosity should be used under specific weather conditions.

Engine Oil Advertising
Engine oil packages would be very plain and similar if only the necessary API Service Classifications and SAE viscosity numbers were shown. To sell the oil, engine oil packages contain many other letters and words that tell very little about the oil within (Figure 2). Also, personal testimonials by non-experts are used to sell oil. Some service people and sales personnel are very knowledgeable while others know less than the information in this fact sheet. Know your engine requirements from your owner or service manual and shop for the correct API Service Classifications and SAE viscosity.

Figure 1. Official API Symbols show both the API and SAE official information. The symbol may be imitated to suggest official testing to the buyer.

Figure 2. The API Service Classification and SAE viscosity values are often shown on the front and back of the label.

Be cautious about advertising phrases that talk about an oil's ability to save gas, reduce engine friction, or reduce engine wear. Do not go by advertising claims alone. Instead, look for the API label to find the best oil. The American Petroleum Institute labels energy conserving oils with the designations "Energy Conserving" or "Energy Conserving II" displayed within the API symbol (see Figure 1). These designations mean the oil gives at least 1.5 percent or 2.7 percent, respectively, fuel savings over a standard reference oil. On an annual basis a consumer might expect 1 to 3 percent less fuel consumption with these oils.

Many oils advertise that they are "high-detergent," "fight sludge," or have a "superior cleansing agent." All good oils have detergent/dispersants blended in at the refinery. These will prevent new deposits but are not going to remove years of old deposits. They are not intended to clean the engine.

Combinations of numbers and capital letters such as: "APP," "fortified with A-9," and "HD" are also found on most engine oil packages. These reveal little about oil quality. Many are product codes companies use for their different oils or additives. The popular belief is that "HD" means heavy duty or high detergent but it, in reality, has no meaning. The "SG" or "CE" rated oils are heavy duty, in a sense, because they are the best oils currently available.

Engine Oil Life
Engine oil does not last forever. While checking on the correct oil to use, check also on the allowed service life of the oil and oil filter for the engine as given in the operator's or owner's manual. The service interval will likely be specified for both a normal and for a severe engine load or environment. Changing the oil and oil filter at the correct intervals for the service conditions are also important.

Don't be confused by engine oil advertising. Check the owner's or service manual for the API Service Classification and SAE viscosity specified for your engine. If you find these two items on an engine oil label, you have found the oil you need.

(Adapted from "What Engine Oil Labels Tell You," Agricultural Engineering Fact Sheet PM-103, 1990, James W. Garthe and Debra J. Hutson, The Pennsylvania State University, 4 pp. and from Bach, Fred, Selecting and Using Oil Instructional Materials Service, New York State College and Agricultural and Life Sciences, Cornell University, Ithaca, NY.)
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