Specially engineered for classic cars. Contains high levels of ZDDP, top-tier additives and rust inhibitors to protect your passion, deliver maximum performance and keep your classic engine free of rust and corrosion in storage.
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Product data sheets
View, download, or save a copy of the Product Data Sheet or Safety Data Sheet for AMSOIL Z-ROD® 10W-40 100% Synthetic Motor Oil.
AMSOIL Z-ROD 10W-40 is a 100% synthetic motor oil engineered for classic cars, hot rods, muscle cars, and high-performance street vehicles that run flat-tappet camshafts. The formulation pairs high zinc and phosphorus anti-wear chemistry with a dedicated rust and corrosion inhibitor package, making it suited for owners who alternate between summer driving and long-term garage storage.
High zinc and phosphorus protect flat-tappet cams
Lifters and cam lobes on flat-tappet camshafts slide rapidly against one another, producing concentrated friction and heat at the contact patch. These surfaces are splash-lubricated rather than pressure-fed, which puts unusual demand on anti-wear chemistry. Z-ROD 10W-40 carries elevated levels of zinc dialkyldithiophosphate (ZDDP) that exceed the limits of API SM and newer service categories, helping prevent the cam wear that otherwise costs valve lift and cylinder pressure.
Bench testing confirms the wear protection. In the Four-Ball Wear Test (ASTM D4172) at 40 kgf, 75 degrees C, and 1,200 rpm, Z-ROD 10W-40 produced a 0.33 mm wear scar diameter, a measure of metal-on-metal protection under sustained sliding load.
Long-term rust and corrosion defense for stored engines
Classic cars and hot rods often sit for weeks or months between drives, and humid garage air drives oxidation on cam lobes, cylinder walls, and valvetrain components. Z-ROD 10W-40 carries a unique blend of rust and corrosion inhibitors built for that storage cycle. In the Standard Test Method for Rust Protection by Metal Preservatives in the Humidity Cabinet (ASTM D1748-10), the metal coupon treated with Z-ROD 10W-40 showed no signs of rust, based on in-house testing of Z-ROD 10W-40 against a leading competitor obtained on 7/25/2019.
Resists thermal breakdown under hot street use
Vintage engines running aggressive ignition timing, richer jetting, or extended idle on a summer cruise night generate significant under-hood heat. Z-ROD 10W-40 holds a flash point of 242 degrees C (468 degrees F) and a fire point of 260 degrees C (500 degrees F) measured by the Cleveland Open Cup method (ASTM D92). NOACK volatility is 3.1 percent weight loss (ASTM D5800), which limits the lighter base oil fractions that boil off at high oil temperature, supporting consistent viscosity and reduced oil consumption between changes.
Stable viscosity from cold start to operating temperature
Cold starts on a long-stored engine are demanding, and an oil that flows quickly protects bearings during the first revolutions before pressure builds. Z-ROD 10W-40 has a pour point of -39 degrees C (-38 degrees F) by ASTM D97, with a kinematic viscosity of 14.9 cSt at 100 degrees C and 97.5 cSt at 40 degrees C (ASTM D445). The viscosity index of 159 (ASTM D2270) and high-temperature high-shear viscosity of 4.3 cP at 150 degrees C (ASTM D5481) together support a stable oil film once the engine reaches operating temperature.
Compatible with conventional and synthetic motor oils
Z-ROD 10W-40 is compatible with conventional and other synthetic motor oils and is safe for automotive seals. Mixing with other oils will shorten its service life and reduce the storage-protection benefits, so straight refills are the preferred practice. Aftermarket oil additives are not recommended; the additive package is already balanced for high-zinc operation, and added supplements can disrupt that chemistry.
Recommended applications and service intervals
Z-ROD 10W-40 is intended for engines that call for either 10W-30, 10W-40, or 20W-50 motor oil meeting an API SL or earlier service category. The elevated ZDDP exceeds the phosphorus ceiling defined by API SM and newer specifications, which is the same property that makes the oil right for older flat-tappet engines and unsuited for modern catalyst-equipped engines that require an API SP, SN PLUS, or SN class oil. Confirm the correct viscosity and service category against the owner manual using the AMSOIL vehicle lookup guide.
Maximum drain interval: 5,000 miles or two years, whichever comes first.
Owner-determined intervals: because classic, hot rod, and performance engines are commonly modified, the owner is responsible for shortening the interval based on tune, fuel, and storage conditions.
Excluded service: engines that require a current API SP, SN PLUS, or SN service category, racing-only engines, and alternative-fuel applications outside the API SL or earlier scope.
Outside the United States and Canada, confirm local availability and viscosity recommendations through the AMSOIL international site.
Pair Z-ROD 10W-40 with a quality oil filter sized for the engine, change the filter at every oil service, and avoid stacking aftermarket zinc supplements or friction modifiers into the sump.
Typical technical properties
Property
Value
Kinematic viscosity at 100 degrees C, cSt (ASTM D445)
14.9
Kinematic viscosity at 40 degrees C, cSt (ASTM D445)
97.5
Viscosity index (ASTM D2270)
159
Flash point, degrees C (degrees F) (ASTM D92)
242 (468)
Fire point, degrees C (degrees F) (ASTM D92)
260 (500)
Pour point, degrees C (degrees F) (ASTM D97)
-39 (-38)
NOACK volatility, percent weight loss (ASTM D5800)
3.1
High-temperature high-shear viscosity at 150 degrees C, cP (ASTM D5481)
4.3
Four-Ball Wear at 40 kgf, 75 degrees C, 1,200 rpm, 1 hr, scar diameter, mm (ASTM D4172)
0.33
Total Base Number (ASTM D2896)
9.0
Order AMSOIL Z-ROD 10W-40
Z-ROD 10W-40 ships in a one-quart bottle (ZRDQT-EA) and a case of twelve quarts (ZRDQT-CA), backed by the AMSOIL Limited Warranty. Match grade and viscosity to the engine's owner-manual recommendation with the AMSOIL vehicle lookup guide, compare the broader passenger-car lineup in the AMSOIL car oil guide, and place an order through the AMSOIL Z-ROD 10W-40 100% Synthetic Motor Oil product page.
after getting a new mower I decided to do things a bit different. I used a break-in oil for the first 10 hours and then switch to the Z-Rod oil. mower engines use a flat tappet cam, so this is going to help it live. I've read several stories that some engines have issue with the cams failing, heard that before. So, this is my attempt to get this thing to live a long life, because nothing is getting cheaper, just made cheaper.
By Allen from OK on July 17, 2026.
Would recommend this to a friend.
Excellent product
I switched from Dominator to Z-Rod to get the added moisture protection since moving to SC. SC is humid and the car sits for long periods. Z-Rod provides all the protection of Dominater for my 800+ RWHP engine both running and sitting.
By Philip from South Carolina on June 08, 2026.
Would recommend this to a friend.
Amsoil Z-Rod
Love this all works great and does what it’s supposed to …
Is high-zinc motor oil good for classic cars and flat-tappet cams?
Yes. Engines with flat-tappet cams depend on splash lubrication at the cam-and-lifter contact, where ZDDP anti-wear chemistry carries the load. Z-ROD 10W-40 carries ZDDP levels above the limit allowed by API SM and newer service categories, which is the formulation point that makes high-zinc oils appropriate for these older engines.
Can synthetic oil be used with a flat-tappet cam?
Yes, provided the synthetic carries the right additive package. Z-ROD 10W-40 is a 100% synthetic formula built specifically around high-zinc, high-phosphorus chemistry for flat-tappet cams, lifters, and rockers, so the synthetic base oil and the ZDDP work together rather than against each other.
What does the high zinc level actually do?
Zinc dialkyldithiophosphate forms a sacrificial film on rubbing metal surfaces under load. On flat-tappet cam lobes the film carries the contact pressure that a splash-lubricated oil film alone cannot, which limits scuffing and lobe wear and helps preserve compression and horsepower over time.
How does Z-ROD 10W-40 protect an engine in long-term storage?
The formula carries a dedicated rust and corrosion inhibitor package built for the humidity cycle a covered classic sees in a damp garage. In ASTM D1748-10 humidity cabinet testing, the coupon coated with Z-ROD 10W-40 showed no rust formation, based on in-house testing against a leading competitor obtained on 7/25/2019.
What is the recommended drain interval for Z-ROD 10W-40?
The maximum service guideline is 5,000 miles or two years, whichever comes first. Because classic, hot rod, and performance engines are commonly modified, the owner is responsible for choosing a shorter interval based on tune, fuel quality, blow-by, and how often the car sits between drives.
Can Z-ROD 10W-40 be mixed with conventional or other synthetic oils?
Z-ROD 10W-40 is compatible with conventional and other synthetic motor oils and will not damage the engine if mixed in an emergency top-off, but mixing shortens the oil's service life and dilutes the high-zinc and storage-protection benefits. Aftermarket oil additives are not recommended.
Is Z-ROD 10W-40 appropriate for modern engines that require an API SP oil?
No. Z-ROD 10W-40 is intended for engines specifying API SL or earlier. The ZDDP level exceeds the phosphorus ceiling defined for API SM and newer specifications, which can shorten catalyst life on modern emissions-equipped vehicles. Modern engines should run a service-current motor oil that matches the owner manual.
