The great seismic shift in engine oils came about as a result of fuel economy and emissions reduction requirements. Before the mid-1970s, engines were big, loose hunks of iron with relatively primitive vacuum and mechanically linked fuel delivery systems. Flat tappets were the king of the hill in valvetrains, and 3,000-mile oil changes were almost universally recommended.

In addition, 70 to 80 percent of oil changes were done by the vehicle owner, Mr. Do-It-Yourself. The only hardware change was the adoption of the positive crankcase ventilator to recirculate blowby gases into the intake manifold.

When lead was removed from gasoline, the needs of the engine oil changed. With lead, there were acidic materials in gasoline to scavenge lead from the blowby gases in the crankcase. With the removal of lead, the scavengers were gone, and the deposits now were due primarily to combustion byproducts. That led to a reduction in detergents and an increase in dispersants. Simply stated, detergents tend to prevent deposits on metal surfaces. Dispersants capture the pieces that will form the deposits (precursors) in the oil and suspend them. Thats what makes your engine oil get dark.

Then 1973 happened, a year which will live in automotive infamy (to paraphrase President Franklin Roosevelt). The first Arab oil embargo occurred, and the abyss was opened. We had lines of cars at service stations waiting to get gasoline. In some places, depending on your license plate, you could buy gasoline on either odd or even numbered days. People were pumping gasoline and not paying. Fights broke out when the pumps ran dry. Congress, fearing that the United States would run short of gasoline, enacted laws mandating fuel economy improvements that were the beginning of the end for the big iron behemoths.

The first thing to fall was viscosity. Where SAE 10W-40 ruled the passenger car motor oil market in the 1970s, by 1980 SAE 10W-30 was making significant gains and SAE 5W-30 was beginning to show up in the market. The shift was made to gain the fuel economy benefits of lower viscosity. The trend continues to this day and influences the use and type of viscosity index improver. Shear stable V.I. improvers, it turned out, are a double-edged sword: Higher shear stability means staying in grade is possible, but lower shear stability enables better fuel economy.

An interesting sidelight to this progression was a program in which I was involved. An additive was developed in the late 1970s that contained only 0.05 percent by weight of phosphorus, no zinc and had a total sulfated ash content of 0.5 percent by weight. The oil was field tested in a fleet of Ford delivery vans at 7,500- to 15,000-mile drain intervals. It worked wonderfully! However, when it was engine tested in an early API Group II base oil, it was unable to pass an ASTM Sequence IIID oxidative stability test. The product was dropped from consideration, even though there were possible additive adjustments that might have fixed the problem.

Emissions controls continued to be developed and included the introduction of catalytic exhaust converters. It soon became apparent that higher levels of zinc dialkyldithiophosphate had some negative effects on catalyst life. Phosphorus tended to poison the catalyst, effectively negating the reduction in emissions that the catalyst was supposed to achieve. In addition, the zinc formed a glass-like compound, zinc pyrophosphate, which physically blocked the catalyst surface, also neutralizing it. That fact led to the reduction of ZDDP in the oil. ZDDP is also an antioxidant, so additional oxidation inhibitors had to be added to make up for lost oxidation protection. The reduction of ZDDP in oil led to concerns about successfully lubricating flat tappet designs.

Engine design moved to roller followers in the valvetrain to gain fuel economy performance. Friction modifiers were added to the oil to improve fuel efficiency, which also helped engines that were shrinking but had higher output and that were designed more precisely, making friction control crucial.

The next great shift was computer control of the ignition process and the introduction of fuel injection. These two went hand-in-hand and were both related to emissions reduction and fuel economy. By 1993, the onboard computer in automobiles had more computing power than the onboard computers of the Apollo space missions.

The last 25 years have been a steady progression of engine design changes and oil formulation improvements to make the new designs work. Ive mentioned before that in 1975, an engine typically delivered 0.5 horsepower per cubic inch. Forty years later, an engine typically delivers 1.0 to 1.5 hp/cu. in. That means my 2008 Nissan 3.5-liter (213 cu. in.) engine, which delivers 240 horsepower, would be equivalent to a 7-liter (426 cu. in.) 1975 engine, assuming I get one horsepower per cubic inch. Youve got to know that higher output engines tend to put more load on the oil.

Currently, there are growing numbers of gasoline-fueled engines in the marketplace that use direct injection, turbocharged combustion systems. These engines deliver an amazing amount of power to the car. The concept is simple: The more air you can inject into the combustion chamber (turbocharging), the more fuel you can ignite (fuel injection) and the more power you can generate. This, however, can lead to low-speed pre-ignition, which can cause high-pressure spikes, loud knocking noises, detonations and even engine damage.

In a paper presented at the 2014 SAE World Congress titled Impact of Lubricant Composition on Low-speed Pre-Ignition (2014-01-1213), authors from Cambridge University and BP International noted that, Although the mechanism leading to megaknock is not completely resolved, pre-ignitions are thought to arise from local auto ignition of areas in the cylinder, which are rich in low-ignition delay contaminants such as engine oil and/or heavy ends of gasoline. These contaminants are introduced to the combustion chamber at various points in the engine cycle (e.g. entering from the top land crevice during blow-down or washed from the cylinder walls during DI [direct injection] wall impingement).

Basically, the oil creates a hot spot in the combustion area, which ignites the fuel prematurely. Youve probably all heard knock before. It can sound like marbles rattling around in the engine or maybe a rumbling sound. Megaknock can tear an engine up pretty quickly and is a real concern to original equipment manufacturers right now. The LSPI test, also known as the Sequence IX, is designed to measure the engine oils ability to minimize this problem. One of the concerns is the ash content of the oil. There are some reports that the type of ash (calcium vs. magnesium) has an effect.

So here we are today, 45 years later (yikes), and oil change intervals are averaging 4,500 to 5,000 miles, and the majority are now done by others (do-it-for-me). Engines are delivering the same power as the iron behemoths but are much smaller and better engineered. Oils have changed from SAE 10W-40 to SAE 0W-20 and are headed down to such viscosities as SAE 0W-8. Engine oils have much different chemistries and are being made from much more highly refined base oils and true synthetics.

This takes me back to that discarded 1970s oil formulation. It was 0.05 percent by weight of phosphorus but it wasnt ZDDP. It had 0.5 percent by weight of sulfated ash, which was a magnesium detergent. At the time, there wasnt an additional antioxidant in it, no friction modifier and it was based on a classic olefin copolymer V.I. improver. I think that the concept should be looked at again and modern additive advances incorporated into the composition. It could be the truly revolutionary oil needed for the most advanced gasoline engine oils.

Is the oil formulation we were looking at in the late 1970s the right way to go? It could be the new Z-7 or some other name. How about X-99?

Industry consultant Steve Swedberg has over 40 years experience in lubricants, most notably with Pennzoil and Chevron Oronite. He is a longtime member of the American Chemical Society, ASTM International and SAE International, where he was chairman of Technical Committee 1 on automotive engine oils. He can be reached at steveswedberg@cox.net.