Oil for Your Classic: What you need to know

If you’ve spent any time reading or listening to stories about changes in oil over the past decade, you’re probably confused, scared, or both. The issue is that changes in oil formulation have reduced the amount of a Zinc additive (zinc dialkyldithiophosphate, ZDDP) and often increased the amount of detergent in modern oils. For awhile there were few oil products available for classic cars, but today, several companies have come out with products specifically designed for older cars.

The primary issue is that the phosphorus in ZDDP is hard on catalytic converters, and exhaust gas recirculation (EGR) systems perform better when there are more detergents and dispersants in the oil. So ZDDP has been reduced, while detergents and dispersants have been increased in modern oils.

For our classic cars, these changes can have a compounding effect. ZDDP is added to oil to coat and protect high-wear surfaces, like the solid-lifter valve trains featured in many classic cars. Increased detergent levels tend to wash away the little ZDDP that is still attempting to protect our valve trains. Finally, modern oils have more friction modifiers to increase fuel efficiency, which can lead to reduced oil film strength and damage parts.

When these oil changes first started occurring, the primary alternatives were diesel oils or racing oils, which contained higher levels of ZDDP than conventional oils. Each of these presented their own problems. Diesel oils have plenty of ZDDP, but unfortunately even higher levels of detergents than conventional oil. Race oils have a good balance of ZDDP and detergents, but lack the anti-corrosion additives that are critical to keep internal corrosion low in little-used classics. 

Today, several specialist oil companies have come out with oils formulated for classic cars. These oils balance the ZDDP and detergent levels adequately and include appropriate corrosion inhibitors to keep our engines from damage whether they’re running or in storage. 

While each specialist company has its own reason for getting into the classic car oil business, one of interest is Classic Car Motor Oil. The development of this product was driven by the Indiana Region of the Classic Car Club of America. Club members approached the D-A Lubricant Company near Indianapolis about the problems of modern oil in classic cars, and D-A worked with them to develop and co-market a specific blend of oil for Classics. Classic Car Motor Oil is now available in sizes from the quart to the case to the 55-gallon drum for enthusiasts with classic cars. The work from this club and this company show that grassroots efforts can yield great results.

While there still may be some confusion about oils these days, it’s reassuring to see that the marketplace is responding with products that will keep our classics living on. Make sure to consider your oil options next time you service your classic car.


Classic Car Motor Oil Company

Driven Racing Oil

Brad Penn Oil

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    The zinc information is false according to an engineer who has done numerous tests on oil. Read “540RAT” blog regarding zinc oils. He busted the zinc theory and proved it was useless after performing numerous oil tests.

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