Why Do You Need Zinc In Your Oil?
At Surf City Garage, we restore vintage cars for our collection. We’ve been doing that for over 40 years. In that time, I can’t even remember how many engines we have rebuilt. Everything from stock Chevrolet 327 small blocks to stroked 1200-horsepower big block screamers. We’ve learned a thing or two along the way about engines, the right combinations of parts, what makes them live under extreme conditions, and much more.
Experimenting has always been our preferred path to the truth about pretty much everything we do. Sure, you can find just about any answer to any question on someone’s website. The problem is that there are usually as many different answers as there are questions. We make full use of technology every day at Surf City Garage, but when we really want to get at the truth, there is no substitute for getting the facts firsthand ourselves.
The moment in 1985 when the Federal Government mandated that all new cars have catalytic converters installed changed everything for every car built before then. Before catalytic converters were used, most engine oil contained zinc and phosphorus to coat and protect the engine’s internal parts – specifically, the camshaft and the lifters – from premature wear. Any engine with a roller cam can’t have this problem because the roller at the bottom of the lifter rides on the lobe of the cam without extreme friction. The bigger problem is that there isn’t one single car built before the widespread use of catalytic converters that has a roller cam. They all use flat tappet hydraulic cams and lifters that make direct contact with the lobes of the cam. These were designed to operate with lubrication, which included zinc, to provide a protective cushion between the camshaft and the lifter base.
So why did the oil companies reduce or remove zinc from engine oil if we need it to protect our engines? Turns out Zinc is bad for catalytic converters – they don’t live as long with zinc running through them. You would think the oil guys and the catalytic converter guys would have worked together on this problem, but the Government was running the show. The EPA is in charge of what comes out of your car by way of emissions. Protecting the environment is something we should all be concerned with, but keeping your engine alive is not what keeps the folks over at the EPA up at night.
To separate fact from fiction and really find out for ourselves how big this zinc-less oil issue is, we did our own experiment. The test mule was a newly restored 1967 Pontiac GTO 400 V8, four-speed convertible. The plan was simple: fill the freshly rebuilt engine with break-in oil and do our normal startup procedure. Fire the engine and take it to 2200 RPM for 20 minutes, then idle down through the RPM range and make any adjustments needed. We then would put a few break-in miles on the engine to seat the rings under load. Next, we’d drain the break-in oil and fill the crank case with a good multi-grade oil without zinc and replace the filter. Next, we were to drive the car under normal road conditions for 500 miles and pull the engine apart to check for wear. The internal components consisted of tried and tested combinations that we knew worked well. The engine ran flawlessly through 50 to 60 miles. But at about 80 miles into the test, we noticed a slight tick that quickly became a knock, which a stethoscope confirmed was coming from the top of the engine.
The engine still made good power and ran fine but seemed to be getting worse with the knock. We pulled the engine and removed all its parts, carefully inspecting each of them. Overall, the internal parts looked as they should, basically new. There was one big exception: the camshaft and lifters. We saw right away that the cam lobes were visibly flat and worn unevenly. The bottom of the lifter base was also worn excessively for an engine with 80 miles on it. The camshaft and lifter set were manufactured by one of the largest cam companies around and we have used this same cam number at least 50 times with no issues at all. The cam pictured is the actual camshaft from our test car.
The results of this test were so convincing to us that we spent the next six months working with oil and lubrication experts to develop our own engine oil with zinc protection. Some may say that is an extreme reaction, but it’s pretty normal here at Surf City Garage. We have to know for ourselves what’s in the bottle. Today, Vintage Car Motor Oil is all we use in every one of our 100+ cars. Shouldn’t you be using it in yours? 10W-40, 20W-50 & SAE30 viscosity classic car oil
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