All Oil Isn’t the Same: 4 Thoughts on Oil for Gas Engines
Some thoughts on oils used to lubricate gasoline-fueled engines:
1. The latest, “highest” API (American Petroleum Institute) rating for oil used to lubricate spark-fired engines is “SN.” The API SN scale originally started with “SA” oils back in the 1930s, then worked up through “SB,” “SC,” “SD,” etc.
The fine print on oil cans says they are “backward compatible,” meaning an SN-rated oil should be safe for older engines. But it’s not. Older, flat-tappet engines require at least 1,200 ppm of ZDDP (a form of zinc) in their oil to protect the tappet/cam lobe interface.
2. Modern oils, from the late ‘70s forward, have around only 800 ppm of ZDDP to avoid a chemical reaction in exhaust gases that can damage catalytic converters. For that reason, older gasoline-fueled cars and trucks need to use special high-zinc engine oil, or use ZDDP additives in their SN-rated oil, to prevent damage to the valve train of engines in their antique, classic or muscle cars.
3. Engine oils made from “Pennsylvania crude” were traditionally considered a higher grade of oil. Pennsylvania crude oils tended to be greenish-colored. According to Eric Peterson with Northland Oil, Pennsylvania crude oils contained higher concentrations of wax, which gave them some natural benefits compared to crudes with lower wax content.
He said modern refining processes have eliminated any advantages one type of crude oil might have over another: “The new procedures have pretty much equalized the end products so that any differences are in the additive packages. If one engine oil is better than another it’s because of the way the manufacturer blends it, not because the base oil is better.”
4. Synthetic engine oils are not automatically better than mineral-based oils. Synthetic oils definitely withstand oxidation longer, which extends change intervals. Well-formulated mineral oils, with quality additives in the right proportions, lubricate engine components just as well as synthetic oil.
Cost wise, in some situations, it’s cheaper to change mineral oil twice as often as synthetic oil, and still be able to maintain proper lubrication.
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