Why AMSOIL
Published numbers, not marketing adjectives
Synthetic oil costs more than conventional, so the claim needs to be backed. Every figure on this page is one AMSOIL publishes, tied to a named industry test method, with the footnote printed right below. If a number is not sourced, it is not on this site.
The published test data
What AMSOIL demonstrates in standardized testing
Water contamination and still protecting
AMSOIL Synthetic Marine Gear Lube delivers excellent gear and bearing protection even when contaminated with 15% water.
More piston protection against LSPI
Even after 25,000 miles of use, AMSOIL Signature Series delivers 4X more piston protection against low-speed pre-ignition than the industry standard requires.
Better protection against volatility
AMSOIL Signature Series delivers 2X better protection against volatility, helping reduce oil consumption and keep engines cleaner over time.
More protection against piston deposits
In Sequence IIIH testing, AMSOIL Signature Series delivers 72% more protection against piston deposits than industry standards require.
Better protection in a double-length test
Even after doubling the length of the Sequence IIIH test, AMSOIL Signature Series provided 31% better protection than required.
Oil screen plugging over 125,000 miles
During a 125,000-mile accumulation study, the test engine running AMSOIL Signature Series experienced 0% oil screen plugging.
Sources and test conditions
- 1Based upon AMSOIL testing of AMSOIL 75W-90 Synthetic Marine Gear Lube in ASTM 3233 and ASTM D892.
- 2Using AMSOIL Signature Series 5W-30 100% Synthetic Motor Oil following a 25,000-mile service interval in the Sequence IX aged-oil LSPI test.
- 3Based on AMSOIL Signature Series 0W-20 100% Synthetic Motor Oil compared to the API SQ limit using the ASTM D5800 Noack volatility test.
- 4Based on AMSOIL Signature Series 5W-30 in the Sequence IIIH Test.
- 5Based on AMSOIL Signature Series 5W-30 in a double-length Sequence IIIH test.
- 6As demonstrated in a 125K-mile accumulation study on a 2025 Ford F-150 Raptor which had 0% plugging.
All performance figures above are published by AMSOIL INC. and are subject to change as formulations and testing are updated. Current product data bulletins and full test details are available on AMSOIL.com.
The Gulf Coast case
Six conditions that make this region hard on engines
National lubricant marketing is written for a temperate average. The Gulf Coast is not average — it is hot, humid, salty and seasonal in ways that change which product attributes actually matter.
Humidity means condensation
An engine that runs hot then sits in humid air pulls moisture into the crankcase as it cools. Water in oil promotes acid formation, rust on cam and bearing surfaces, and additive depletion. Marine formulations are built with corrosion inhibitors specifically for equipment that spends more time parked than running.
Salt water finds every seal
Lower units take on water through worn seals, and nobody notices until the gear oil comes out milky. AMSOIL publishes gear-lube performance under water contamination precisely because this is a known, common failure mode rather than an edge case.
Sustained heat, not occasional heat
A Gulf Coast summer means months of ambient temperatures in the nineties, not a handful of hot days. Heat drives oxidation and volatility. Oil that boils off leaves deposits behind and thickens what remains, which is why volatility resistance matters more here than in a temperate climate.
Ethanol pulls water out of the air
Ethanol-blended fuel is hygroscopic. In a vented tank on a humid coast it absorbs moisture, and past a threshold the ethanol and water separate out and sit at the bottom of the tank where the pickup is. Fuel additives are not optional maintenance down here.
Long storage gaps between uses
Boats, generators and lawn equipment sit for weeks or months. Deposits form, carburetors gum, fuel goes stale and seals dry out. A stabilizer and a fuel-system cleaner cost far less than a carburetor rebuild.
Corrosion is constant, not seasonal
Salt air attacks connectors, linkages, trailer bearings and any exposed steel year-round. Water-resistant grease and a metal protector are the cheapest insurance in the catalog, and the most frequently skipped.
Company background
1972
AMSOIL introduced the world's first API-qualified synthetic motor oil in 1972. It sat on store shelves next to far cheaper conventional oil, and consumers had no frame of reference for what synthetic meant. The independent Dealer network launched in 1973 to explain the difference in person — which is the reason this site exists rather than a shelf tag at a big-box store.
7 AMSOIL INC. company history, published at amsoil.com.
Marine certification
FC-W8
NMMA Catalyst Compatible certified
AMSOIL Marine Synthetic Motor Oil is certified by the National Marine Manufacturers Association for use in four-stroke outboard motors and meets the NMMA FC-W Catalyst Compatible specification, which is backward-compatible with FC-W.
8 Per AMSOIL published product information for AMSOIL Marine Synthetic Motor Oil, NMMA FC-W Catalyst Compatible certified.
Want the data for your specific engine?
Product data bulletins list the exact specifications, approvals and test results for each AMSOIL product. Tell me what you run and you will get the relevant bulletin plus a straight recommendation.