Think About Your Zinc
Have you heard about the zinc problem with modern motor oils? Many classic car owners and racers have experienced camshaft failures due to decreased zinc levels in modern motor oils.
Now, with levels about to change again this fall, it’s more important than ever for engine builders to think about their zinc.
If you’ve not had the pleasure of having your camshaft go flat due to modern motor oils, consider yourself very fortunate. As an owner of an engine parts warehouse, I’ve seen hundreds of perfectly good camshafts ruined by modern motor oils.
So, when I read about the new API SN motor oil coming out this fall, I started talking to the engine builders we supply parts to. They all said the same thing: car owners don’t know much about these modern motor oils and the problems they can cause in classic cars and racecars.
In many cases, modern motor oils are simply not good for classic hot rods and race cars. Here’s why:
“Zinc,” or ZDDP as it is commonly referred to, in motor oils is a type of chemical called Zinc DialkylDithioPhosphate. “Zinc” has been the most common anti-wear additive used in motor oils for the last 60 years. (I’ll just call it ‘zinc’ for the rest of this article.)
Zinc is a remarkable chemical that protects engine parts from metal-to-metal contact under heavy loads. It works by creating a film on the iron and steel parts in an engine.
Unfortunately, zinc also creates a film inside modern three-way catalytic converters. This “Zinc Poisoning” limits three-way catalytic converter life to around 70,000 miles.
The Federal Environmental Protection Agency mandates that car manufacturers warranty three-way catalytic converters on new cars built since 2004 for 120,000 miles. To achieve this goal, the car manufacturers worked with the American Petroleum Institute to create new, lower-zinc oils that allow three-way catalytic converters to live longer.
These new “Lower Emissions” oils have extended catalytic converter life, but they have shortened the life of flat-tappet camshafts.
Not long after these modern motor oils with less zinc hit the market, we started to notice an increase in flat-tappet camshaft failures. At first, it was the race engine builders, so we shrugged it off as some new “trick” the race guys were doing that caused the problem. Then we started to see stock flat tappet camshafts going flat.
Things got ugly really fast. Every camshaft company started researching the problem. So did the Automotive Engine Rebuilders Association. Everybody wanted to know: why are cams going flat?
The answer was less zinc.
Turns out, lower zinc oils work just fine in modern production car engines with overhead cams and roller lifters. These modern engines don’t rev past 5,000 rpm.
On the other hand, most hot rod and race motors have push rods and flat tappet lifters, and rev beyond 5,000 rpm. These engines need motor oil with more zinc.
The good news is that “High Zinc” oils are available.
If you have a classic car or racecar, I highly recommend using a higher-zinc oil. We use the Joe Gibbs brand, and there are others also available.
We have seen a dramatic reduction in camshaft problems when our engine builders started using higher-zinc oils designed for older engines.
Again, if you’ve not had any problems so far, consider yourself very lucky. But with the new formulas scheduled to be released this fall, switching to a high-zinc oil before the new API SN oils hit the shelves is like an insurance policy you’ll be happy you have.
We like selling engine parts, but I hate seeing good parts go bad—especially when they don’t have to.