Old cars can actually benefit more from high-mileage oil than newer models. Combustion gases always leak past the piston rings and into the oil (even in new engines). The gases then condense to form corrosive acids. New engine oil contains enough acid neutralizers, anti-corrosion agents, detergents and foam inhibitors to counteract the effects of normal blow-by. But the extra blow-by in older engines causes the additives to wear out sooner. That’s where high-mileage (HM) oil comes in handy.
HM oils (about 75¢ more per quart) are formulated to handle the extra load and are well worth the money. To get even greater protection, add a high-mileage oil filter, too (the Fram HM is one choice; available through our affiliation with amazon.com). High-mileage filters contain a capsule of additive gel that dissolves slowly over a 3,000-mile period. So it continually feeds new additives into the oil. Together, HM oil and an HM filter add less than $7 to the cost of an oil change. It’s a good investment to keep your old wreck running longer.