AMSOIL Z-ROD® 10W-40 100% SYNTHETIC MOTOR OIL

AMSOIL Z-ROD 10W-40 100% Synthetic Motor Oil delivers high-zinc anti-wear protection and long-term rust prevention specifically formulated for classic cars, muscle cars, and high-performance engines running flat-tappet camshafts. It is built for engines that spend as much time in the garage as they do on the road.

Classic and vintage engines face a different set of problems than modern powerplants. Flat-tappet camshafts rely on a sliding contact between the lifter face and cam lobe that generates extreme friction and heat, and these components are splash-lubricated rather than pressure-fed. Modern motor oils have steadily reduced their zinc and phosphorus content to protect catalytic converters in newer vehicles, which leaves older engines dangerously underprotected in the areas that need it most. On top of that, cars driven seasonally or stored for months at a time are exposed to humidity and moisture that can corrode cylinder walls, bearings, and other internal surfaces.

HIGH-ZINC FLAT-TAPPET CAM PROTECTION
The cam lobes and lifters in a classic small-block Chevy, Ford FE, Pontiac 400, or Oldsmobile 455 operate under boundary lubrication conditions where metal-to-metal contact is inevitable without a strong anti-wear film. AMSOIL Z-ROD 10W-40 is formulated with high levels of zinc dialkyldithiophosphate (ZDDP) that exceed the limits set by API SM and newer specifications. That high-zinc, high-phosphorus chemistry forms a sacrificial protective layer on cam lobes, lifters, rocker arms, and other wear-prone surfaces. In Four-Ball Wear testing (ASTM D4172), Z-ROD 10W-40 produced a wear scar of just 0.33 mm, confirming its ability to minimize metal-on-metal contact under load.

FIGHTS COMPRESSION LOSS AND RETAINS HORSEPOWER
Wear on the camshaft and valvetrain doesn't just damage parts. It changes valve timing and lift, which directly reduces cylinder filling and compression. A worn cam lobe can quietly rob your engine of power long before it shows up as a noise or a misfire. Z-ROD's anti-wear formulation fights that progressive damage, helping the valvetrain maintain the profiles the cam was ground to and keeping your engine making the power it was built to produce.

PREVENTS RUST AND CORROSION DURING STORAGE
A classic car that sits through winter or between shows is vulnerable to moisture condensation inside the engine. Bare metal surfaces exposed to humidity will develop surface rust that pits bearing journals, cylinder walls, and lifter bores. AMSOIL Z-ROD 10W-40 is formulated with a proprietary blend of rust and corrosion inhibitors specifically for this scenario. In the Standard Test Method for Rust Protection by Metal Preservatives in the Humidity Cabinet (ASTM D1748-10), Z-ROD completely prevented rust formation on the test coupon. A leading competitor tested under the same conditions did not. If your 1969 Camaro, 1972 Corvette, or 1965 Mustang spends months under a cover in a damp garage, this is a meaningful difference.

SYNTHETIC DURABILITY WITH CLASSIC-CAR CHEMISTRY
Z-ROD 10W-40 combines the thermal and oxidative stability of a full synthetic base oil with the aggressive anti-wear additive package that older engines demand. Its flash point of 242°C (468°F) and fire point of 260°C (500°F) provide a wide margin of thermal safety for air-cooled or under-cooled vintage engines running hard at cruise nights or on the drag strip. Noack volatility of just 3.1% weight loss (ASTM D5800) means less oil burned off at high temperatures, keeping oil consumption low and maintaining viscosity over the life of the oil. The viscosity index of 159 indicates excellent stability across a wide temperature range, from cold startup to full operating temperature.

SPECIFICATIONS AND COMPATIBILITY
Z-ROD 10W-40 is designed for engines that require 10W-40 motor oil and an API SL or earlier specification. Its ZDDP levels intentionally exceed the limits of API SM and newer ratings, making it the right choice for pre-emissions-era engines rather than late-model vehicles with catalytic converters sensitive to phosphorus. It is compatible with conventional and other synthetic motor oils, though mixing will reduce its performance benefits and service life. Z-ROD is safe for use with standard automotive seals. Aftermarket oil additives are not recommended.

SERVICE LIFE
Because classic and high-performance engines vary widely in modification level and usage patterns, a single drain interval recommendation does not apply. As a general guideline, Z-ROD 10W-40 should not exceed 5,000 miles or two years, whichever comes first. For cars driven infrequently or stored seasonally, the two-year calendar limit is the more relevant benchmark.