What Is ZDDP And Why Is It Worth Buying For Your Antique Car?

Credit for this post goes to Model A.


A good balance of ZDDP (zinc dialkyldithiophosphate), detergent levels, and corrosion inhibitors are important when selecting an oil for your antique car. But, what is ZDDP and why is it worth buying?

ZDDP is an oil additive or component that is critical to flat bottom lifter, flat tappet, and cam lobe longevity in older engines. Modern engines use roller lifters which don’t require ZDDP as they don’t “slide” on the cam lobes the way flat bottom lifters do. ZDDP has been known to poison the catalysts in catalytic converters and was phased out of gasoline engine oils. Now that diesels use exhaust treatment devices, ZDDP has been phased out of all engine oils for on road use.

While most antique engines like Model T and Model A with extremely low compression ratios do not have excessive valve spring tension to exert on their tappets and cam lobes, some still feel better using ZDDP in their cars. I personally feel a big block from the muscle car vintage should use ZDDP additive or “cam oil” to protect the lifters and cam, as these engines had higher horsepower and stronger valve springs and used flat bottom lifters.

For more information, here are some good articles:

Oil for Your Classic: What You Need to Know

Classic Motor Oil

So... what do you think? Please leave me a comment.

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