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Oil not only lubricates an engine, it also cleans
&; protects it, and helps carry away heat developed by friction. About
20% of the oil in your engine is additives intended to help the oil hold
up under the strain of heat, prevent oxidation, and combat contamination
from moisture. Moisture comes from condensation of the combustion process.
Demonstrate this to yourself: hold a cold dinner plate over the burner
on a gas stove. An engine produces a lot of water in the first few minutes
after a cold start, but after it warms up to temp, the amount is quite
a bit less. Water combines with oil to create acids and sludge, which will
destroy any engine given a little time. The additives combine with these
acids and water to render them less harmful, but depending on the manner
in which the vehicle is driven, these additives eventually are used up,
and the viscosity (the relative "thickness") of the oil is changed, and
never for the better.
So changing the oil (and the filter, which holds up to a fourth of the engine's oil inside it) now &; then will get rid of the acids &; sludge, and restore the original viscosity. Like a blood transfusion or washing the dishes?
I recommend changing the oil every 3,000 miles whether it needs it or not, but usually it needs it, no matter what it seems to say in your owners manual. If you examine that tome a little more closely, you will likely see that it recommends a much longer interval, such as 7,500 or even 10,000 miles, but it will also say "under normal conditions". Then it will give a much shorter period (like 3,000 miles) for "Severe Service", and go on to explain what severe service is , such as if:
Most trips are less than 4 miles in warm weather or 10 miles in cold
weather.
Letting the engine idle for a long time or stop &; go and low speeds
as in heavy traffic.
Driving in heavily polluted or dusty conditions like dirt roads.
Towing a trailer.
Carrying heavy loads.
Driving at sustained high speed , especially in hot weather.
Diesel, turbo, or turbo diesel engines.
Sounds about like what most of us do all the time
It used to be that oils only came in a single viscosity,
such as SAE 40, SAE 30, SAE 20/20W, &; SAE 10W. The larger the number
the heavier the viscosity, or to say it another way, the oil is thicker
as the numbers go up. Generally, the lower numbers are for cold weather
use, and vice versa. Now they are combined in multiviscosity oils, like
20W50, 10W40, 10W30, and 5W30, meaning the oil will serve over a wider
temperature range. Where you once changed to "winter grade" oil in the
fall and back to "summer grade" in the spring, you can now use the same
oil at any time of the year. Most manufacturers are now recommending 5W30
oil for year round use, even in fairly heavy duty applications. The idea
is that it flows more readily under both hot and cold conditions, providing
initial lubrication earlier when a cold engine is first started, and carrying
away heat more efficiently when the engine is hot. It also creates less
friction or drag on internal engine parts, allowing better fuel economy
and slightly more power output, too.
Oil Specifications
The markings on a can of oil have a meaning, (surprise, surprise). In the old days there was only non detergent oils. Then came high detergent, with the designations ML, MM, &; MS to consider. Now these are out the window, and we have API specifications for spark ignition engines such as SB, SC, SD, SE, SF, &; SG oils. These are combined with specs for diesel engines; such as CB, CC, CD, CE, &; CF oils. ("API" stands for American Petroleum Institute.)
If you hadn't already figured it out, the "S" stands for "spark ignition", and the "C" stands for "compression ignition", which is the basic difference between gas and diesel engines. The second letter of the designation stands for the level of service duty expected of the engine it will be used in, "B" being the lightest duty, and rising from there. Usually, the manufacturer of an engine will issue standards for each engine they build, and make recommendations for which oil to use according to these API specifications.
If you compare the recommendations in your car owners manual to the markings on the cans you get from the discount store, you might find that the oil you are using is not as good as it should be.
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