KA: There’s a government requirement that every modern engine and its emission control components must last at least 100,000 miles. Zinc and phosphates degrade the oxygen sensors and the catalytic converters on modern engines. So the oil makers have removed ZDDP (Zinc Dialkyl DithioPhosphate) from the motor oils that are commonly sold in stores. The API specification for motor oil won’t allow it any more.
PR: Why is this an issue for older cars?
KA: ZDDP was used for over 50 years. Because of very high pressures between the cam and tappets. Engines were designed to use oil with ZDDP. The zinc is deposited, compliments of the phosphate, on the cam lobe and the follower to provide a sacrificial barrier, to prevent metal-to-metal contact. It may also improve ring contact.
PR: So what oil should we use for our older cars?
KA: Your older car needs over 1200 PPM (Parts per million) ZDDP. Right now, there are only two mainline oils that meet this standard. Those are Castrol Syntec 20/50 Classic and Valvoline VR1 20/50. It’s important to get the Syntec 20/50 Classic, and not the general Syntec 20/50 if you choose the Castrol. Remember that the Valvoline is a natural oil and the Castrol is synthetic. Also, Joe Gibbs Racing Oil is now producing street oils that seem the best available for our engines and distribution of this product is just starting in North America. Red Line Oil, a smaller manufacturer on the West Coast, is available at many racing shops, with 10W-40. Eastern States seem to be able to find Brad Penn Oil, Swepco and Hi-Z.
PR: Is this true for all engines?
KA: Some diesel engines need ZDDP on the wrist pins. We used to be able to use Delo and Rotella diesel oils until about a year ago. But now they’re putting catalysts on diesels, so those oils are out.
PR: Is this just for break-in, or throughout the life of the engine?
KA: The whole life of your engine. But break-in is a whole different story. You still need ZDDP, but you don’t want a modern oil. Oils are so much better now than they were in the 60s and before, that our cars won’t break in on a modern oil. So we used Castrol HD30 for break-in, for 3,000 miles. We add ZDDP and use cam lube.
PR: Are there additives you can use to put ZDDP in your oil?
KA: I like two additive products on the market. One is Cam Shield, made by a startup company, led by an expert chemist and spun off of a racing enterprise. We’re the west coast distributor for Cam Shield. Another product is ZDDPlus. ZDDPlus was made back east by a place that specializes in turbo Buicks.
PR: What does it cost?
KA: The two manufacturers are comparable. It costs about $9 to $12 per 5 quarts to treat the oil correctly.
PR: With the additive, can you use any brand of oil?
KA: First of all, multi-grade oils are vastly superior to single grade. The other thing is detergent vs. non-detergent oils. People should use multi-grade detergent oils unless they have a brass era car - 1918 or earlier. For most all old engines, we like 20/50. Other than that, it’s mostly just branding and the additive package that makes a difference. So use any oil you prefer. If the automaker says to use Castrol, then use Castrol, but put your ZDDP additive in. One exception: If you have been running a non-detergent oil it might be advisable to stay with what you have been using until a new engine is built.
PR: Is there anything else we should know?
KA: For the cars that use engine oil in their gearboxes, the lack of ZDDP may pose a problem, as these additives could be very critical in preventing gear wear. We will be using oil specifically formulated for manual gearboxes with brass synchronizers. The only oils we are aware of that fit the criteria are from General Motors and Redline.
