How long can motor oil be used without changing? This has been a popular question ever since the early days of the automobile. Developments in the past few years have made this question even more prevalent.

Many motorists are now asking: “With all the advertising about new and improved motor oils, why can’t they be used a lot longer between drains?”

Other questions involve the many varieties of crankcase “gadgets” which are on the market. Some of the “gadgets” are claimed to neutralize acids, and others to prevent oil oxidation or deterioration, with claims that motor oil can then be used from twenty-five to fifty thousand miles or even with no oil changes at all!

Quaker State Motor Oils are fortified with inhibitors to give them remarkable stability and resistance to oxidation and deterioration. They also contain acid neutralizing additives to eliminate any fears of acidity or engine corrosion.

Quaker State Motor Oils won’t break down, or wear out, or become acid under normal operating conditions in a passenger car engine. So why bother to change oil? Unfortunately, the answer to this question is not short or simple.

Motor oil must perform two primary functions. It must lubricate the engine, which is obvious; but it also has to serve as a collector of contamination. Summed up in a few words, good motor oil won’t wear out, but it can be contaminated to death. So the question is: What is this contamination and where does it come from? T comes from the engine combustion chambers where the gasoline is burned to produce powder.

We’re faced with two different types of fuel combustion in engines: efficient combustion or clean burning; and inefficient combustion or dirty burning. If you’re old enough, you may remember the kerosene lamps your grandmother used, or maybe it was your great-grandmother. Anyway, if the lamp wick was trimmed and adjusted properly, she got a clean, bright flame; but if the wick was ragged and scorched or turned up too high, the flame was dull and smoky and the lamp globe quickly became coated with greasy soot. Strangely enough, these same differences exist in engine combustion chambers and have a vital effect on the crankcase oil.

But just as a modern engine is a lot more complicated than an old-fashioned kerosene lamp, so is this problem of dirty burning in engines a lot more complicated. When dirty combustion occurs in engines, soot isn’t the only thing formed. Sticky, gummy products, which oil chemists call resins, and lead oxyhalides. Small quantities of acidic combustion products are also formed. Last, but by no means least, is water. For every gallon of gasoline burned, a little over one gallon of water may be formed, believe it or not! So during the burning of gasoline in engines, we have a potential problem with soot, resins, acids, and water which are formed. If these combustion products work down past the pistons to get into the crankcase oil, then we do have the problem of dirty, contaminated oil. If the oil is allowed to become too dirty and contaminated, sludge deposits will form to cause plugged piston rings, oil pump screens and oil filters. Engine wear and even engine damage can then result.

So now you may ask, “When does dirty combustion occur, and when does the contamination work down past the pistons and get into the oil?” The answer is when the engine is cold. An engine used in typical city driving with a lot of short runs, stopping and starting, seldom gets a chance to warm up thoroughly and operates at its lowest efficiency, which means dirty combustion. The cold cylinder walls of the engine act as condensers for the soots, resins, water and unburned gasoline. These are washed down past the pistons into the crankcase oil. An engine has to have a good, steady run before it is thoroughly warmed up, and a considerable longer time in winter. The first few minutes after each cold engine starts is the hardest on the oil.

After an engine has been run long enough to get thoroughly warmed up, it’s then operating at its best efficiency, which means clean combustion and a minimum of combustion soots and contaminates. Furthermore, the hot cylinder walls no longer act as condensers, so the contaminates are minimized and don’t work down past the pistons into the crankcase oil.

Contrary to popular belief, a truck, bus or passenger car driven at highway speed on a long trip is the easiest job to lubricate and the least demanding on an oil of good quality. The really tough lubricating job is the engine, which gets only short runs with lots of stops and starts, especially in cold weather.

Did you notice something? The worst conditions for both the engine and the oil are the very conditions under which the great majority of passenger cars are used most of the time.

Oil changes are necessary, not so much because oil wears out, but chiefly to flush contaminates from the engine before they build up to dangerous concentrations.

If a car is used for a lot of steady cross-country driving, where the engine runs hot and efficiently, a good oil can be used for 7500 miles and longer. But, if a car gets most of its use in town with many cold starts and few long runs to get it really warmed up, then oil changes every 90 days are good life insurance for the engine, and that’s especially the case during winter driving. Maybe a car owner can get away with using oil longer, but after all, oil is pretty inexpensive when you consider the important job it has to do. One engine repair job can cost a lot more than all the oil needed for several year’s safe lubrication.

Most car manufactures recommend oil changes at the end of a specified mileage or after a certain time interval, whichever comes first for specific driving conditions. This type of recommendation permits the high mileage driver who operates his car under favorable conditions to change oil at fairly high mileage intervals. It also insures that the stop-and-go type of driver who operates his car under unfavorable conditions changes oil at regular time intervals before contamination becomes excessive.

At improvements are made both in engine design and lubricant formulation the car manufactures extend their recommendations. With specially formulated oils such as Quaker State Sterling Motor Oil even longer drain intervals are possible and the car manufacturers will be recommending longer drain intervals when oils of this quality are used.