Synthetic vs. Mineral Oils - Changing Oil Preference

The customers in my shop, as well as many readers of Machinery Lubrication magazine have asked for guidance when deciding whether to use petroleum (mineral-based) or synthetic oil in their vehicles.

I’ve hesitated to comment on the virtues of one over the other because I was in a state of change; I am changing my mind about synthetic oil. Synthetic oil has become my first choice for cars, especially for newer cars.

In previous articles, I have presented strong convictions about oil. I have argued the pros and cons of multi- and single-weighted oils.¹ Yet, I have avoided choosing between mineral-based oils and synthetics. It was only on the Noria Web site message boards that I stated my preference for mineral-based lubricants.

Why? Because I was still trying to resolve “my final answer” on the question.

As with most decisions in life, this one was based on money. But other considerations also influenced the outcome: money, personal enrichment from continuing education and peer pressure have changed my mind about changing oil. Simply said, the three reasons for change are money, new knowledge and deciding to go with the flow of my fellow mechanics.

Cost Per Quart

The common price for a quart of 10W-30 brand-name petroleum-based oil at a local auto parts store is $2.25. The common price for brand-name synthetic oil is $4.95 per quart - about twice the price of petroleum oil.

Why would I want to pay twice as much for engine lubrication? I have to admit that synthetic oil lasts longer. The reason it lasts longer is not because petroleum oil wears out. I can remember re-refiners in previous decades that collected waste oil and refined it to a usable form. This was before we used the modern term “recycle.” It was certainly better than spreading the wasted oil on dusty roads.²

Synthetic oils have proven that they can last far longer than twice the recommended 3,000-mile oil change and still maintain their lubricant qualities.

I grew up in this business at a time when a car that lasted 120,000 miles was a phenomenon. Reaching 200,000 to 300,000 miles is now becoming the norm, and why not? My father bought an air-conditioned 1955 Chevrolet for $2,000. My first new car was a 1970 Grand Prix for which I paid $5,600.

I bought a new 1976 Volkswagen van with no air conditioning, and a stick shift for about $6,800. (I put a fuel-injected 2.0-liter Porsche 914 four-cylinder motor in it, and WOW - it was a fun car!) It would cost me about $32,000 to replace my wife’s Buick Park Avenue with a 2004 model.

When I used to change a lot of engines in the 1970s and 80s, the typical bill would run about $1,800 for installation of a remanufactured engine. That price has more than doubled today. The reason is that engines are much more complicated now than they were then. Overhead cams, aluminum blocks and heads, exotic intake and exhaust manifolds, and compact and precision engine compartments have added to the total bill. Anything to protect and extend the life of these components must be considered.

Graph these figures and you will see why it is cheaper to invest $5.00 in a quart of synthetic oil; it will extend the life of your engine and require less frequent lubricant changes.

Why Do Synthetic Oils Often Last Longer?

Heat and oxidation are the primary reasons for oil break down. Petroleum-based lubricants are mixtures of several sizes of hydrocarbon molecules, sulphur, paraffins, salts and metals.

With different evaporation, oxygenation and burn points for each size and type of molecule, the refined petroleum-based oils start changing to an extent the moment you start your car.

In time, a lubricant will have a diminished ability to perform its job, which is to lubricate metal-to-metal contact surfaces in machinery and to transfer heat away from the area being lubricated.

The diminished ability to lubricate increases as the molecules of various size and weight are consumed by evaporation and oxidation. Lubrication ability may continue to diminish as these various molecules interact with the blow-by gases and other contaminants in the engine environment.

Additives are used to control acid, stabilize viscosity, and keep soot in suspension. The additives are typically consumed as they do their job. Therefore, in many cases, but not all cases oil needs to be changed at familiar intervals of 3,000 or 5,000 miles.

Synthetics are more uniform. Synthetic oils are much more thermally stable as a result of this uniformity. For instance, synthetic oils need lessVI improver additive to keep their viscosity stable. Synthetic oil additives may be higher quality or at least work longer.

Synthetics may have better viscosity film strength than petroleum stocks at elevated temperatures (greater than 176°F/80°C). Film strength indicates a lubricant’s ability to occupy the space between two metal surfaces under pressure or heat.

This is the fundamental reason for lubrication, to hang in there and do the job. Higher film strength was one of the factors that changed my mind about changing oil.

However the final straw is the fact that many synthetics have a much higher base number (BN) retention than petroleum-based formulations. The BN is contributed by overbase additives such as detergents and is a measure of a lubricant’s ability to neutralize acid.

The longer a lubricant can resist turning to acid, the longer it can be used. This fact, along with the decreasing cost differential of the two lubricants, is reason enough to use synthetics.

Going with The Flow

I and my fellow mechanics are awakening to the idea of extended oil drain intervals. The quick-lube shops and petroleum oil manufacturers are naturally going to resist the idea for their own economic interests. But weighing the upward spiraling costs of today’s oil and gasoline, the synthetics with their better protection and extended drain intervals are looking good.

Briefly, I want to add that oil filtration must be the very best if you are going to practice extended drains. I will discuss oil filters in an upcoming issueof the magazine, because they are important enough to have an article devoted exclusively to their role and performance.

To those who are wary of suddenly extending your oil drain intervals, I would recommend to use oil analysis to confirm the results. 

Long ago I advocated frequent oil changes because I believed that a skilled person should look around under the car as he greased and changed the oil. My 1970 Grand Prix had 13 grease fittings; my wife’s 1998 Buick has two.

Not much time for a look-see. Most components are designed for low to no maintenance. Maybe my services are not needed as much in prevention as in repair. Like Bob Dylan wrote, “the times they are a-changing.”

Related Reading

1. Ramsey, P. “Multigrade Oil - To Use or Not To Use.” Machinery Lubrication, July-August 2001.
2. Ramsey, P. “A Breath of Fresh Air.” Machinery Lubrication, September-October 2001.