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9.2 SELECTING THE CORRECT MOTOR OIL; AUTOMOBILE REPAIR AND MAINTENANCE
By
Don Patten
Don
Patten is a leading expert in automotive education. His text book Automotive Service
Basics published by Prentice Hall is used in automotive instruction courses world
wide.
==
Oil Functions:
Everyone
that drives a vehicle has an opinion about what motor oil to use. They may be right but
this depends on whether there have been any motor oil changes since they formed their
opinion. New oils are being developed yearly. Most of these were developed to solve past
problems. Motor oil performs several functions when used in the engine. The most important
is a lubrication which reduces friction and wear. The oil coats the parts and keeps them
from touching each other. Another function is to keep the engine cool. This is especially
important in air cooled engines. The oil absorbs heat and passes it off through the oil
pan. The third function is to act as a sealant. There is an oil seal formed between the
piston rings and the cylinder walls. This helps prevent compression loss.
==
Oil Additives:
Another
part of motor oil chemistry is the additives. Detergents are added which dissolve engine
dirt, sludge, and varnish deposits. Dispersants keep any dirt suspended in the oil so it
can enter the filter and be trapped. There are viscosity index improvers and pour point
depressants which make the oil sensitive to temperature and ability to pour. Inhibitors
are added to prevent oxidation, rust, and corrosion. Other additives reduce foaming and
improve lubricating qualities. How is the motorist able to sort all this out and get a
motor oil that will meet his needs? == Oil Quality:
Check
the service classification label on the oil container. Look for two letters starting with
"S" which means Service Station. The next letter is the quality of the oil. Up until
recently the best classification was "H." We now have a new classification, and it is
"SI." As new classifications are made, they will continue along the alphabet and the
letter "J" will be used. This oil is now being developed and will be the next product
introduced. A typical classification would be "API Service SI/CF-4." Classifications "A
through H" are older oils and should not be used when SI oils are recommended.. Quality is
also measured by the American Petroleum Institute. This is a star burst seal placed on the
container. When you see this, the oil has been developed to high quality standards and
should perform well.
==
Weather and Engine Condition:
Weather
extremes require different viscosity oils. Generally speaking, colder temperatures require
the use of thinner (lower viscosity) oils. We now have multi viscosity oils. An SAE 10W -
30 viscosity oil would be an excellent selection for zero up to 100 degrees Fahrenheit.
Every owner's manual for your particular vehicle will have a section that recommends motor
oil and the correct viscosity for the season and temperature. Follow this advice. Many
owners use an SAE 5W - 30 viscosity motor oil in the summer. This oil is NOT recommended
when the outside temperature exceeds sixty degrees Fahrenheit. When there are extreme the
weather conditions, viscosity changes are recommended. Heavy viscosity oils cause problems
in the winter. They do not flow as well and take more time to circulate in the engine.
Engine damage can occur if a brief engine warm up time is not allowed. As the engine parts
wear, thicker viscosity oils should be used. A change from SAE 10W - 30 to SAE 20W - 40
may be necessary for the same outside temperature. This is a change from the normal
recommendations and should be communicated to those servicing your vehicle.
==
Oil Change Frequency:
Always
follow the manufacturer's instructions concerning oil change frequency as a starting
point. This can be extended if both the filter and the oil are changed at the same time
but reduced if the filter is not changed each time. Changing both the oil and filter every
3,000 miles is the best plan. Additives in the oil get depleted, and acids, dirt and
sludge start to build up when time intervals between changes is extended.
==
Oil Level Checking and Filling:
Always
perform frequent oil level checks in between oil changes. The ideal time is in the morning
after the vehicle has been parked overnight. Place the vehicle in a level area and keep
the motor off for at least three minutes. This lets the oil drain back into the pan so an
accurate check can be made. Pull the oil dipstick out and wipe it off with a clean cloth.
Examine the stick and look at the markings to find the low and full marks. Put the stick
back into the engine and remove it. The level of the oil is the height the oil dampens the
end of the stick. If the oil is below the "LOW" or safe driving range, add the right
viscosity and quality motor oil into the engine until the oil level reaches the "FULL"
mark. It normally takes one quart of oil to go from the "LOW" mark to the "FULL" mark.
==
Oil Problems:
Always
look for additional problems when checking motor oil. Black thick oil could mean the oil
change frequency is not often enough. A white thick substance in the motor oil is an
indication that water is entering the oil. This is a serious problem and should be
investigated further. On engines with mechanical fuel pumps, fuel can enter the engine if
the pump is defective. This will show up as gasoline in the oil. The level will be way
over the full mark and the oil will be thin. It will have a gasoline smell. Blue smoke out
the exhaust means that oil is entering the combustion chamber and being burned.
==
Additional Recommendations:
One
rule to remember, is always buy the best quality motor oil available if your vehicle is in
good condition. It can be damaging to an engine if a lesser quality is used when a higher
quality was developed to solve problems. Follow manufacturer's directions on viscosity.
SAE 10W - 30 is a good starting point for automotive engines when you are not sure. This
can be used in a wide range of temperature differences. It also can stand high
temperatures. Oil additives are not needed if a frequent oil change plan is followed. (You
should always develop an oil change plan for every vehicle and motor you own). There are
additives in each quart of high grade motor oil. It is not recommended that multi
viscosity motor oils be used in air cooled engines such as lawn mowers. SAE 30W is a
widely recommended oil for this use. Just because you have a can of motor oil sitting on
your storage shelf does not mean that it is suitable for every motor you own. Follow the
guide lines and instructions for your automobile and you should have happy motoring during
the life of your vehicle.
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