Most motor oils only provide minimal protection against damaging engine rust and corrosion.
The effects of rust and corrosion are easy to see on the exterior of vehicles and equipment. However, they can also form on the inside of your engine if you’re not using a properly formulated motor oil.
The problem is especially problematic in engines used in applications that sit idle for extended periods, including the following.
Despite what most people assume, motor oils have no natural ability to protect against rust or corrosion. Instead, special rust and corrosion inhibitors must be added to the formulation to provide the required protection, and some oils simply don’t contain the correct additives in the correct concentration.
Idleness equals no protection
During engine operation, a layer of oil coats engine parts and the crankcase walls. The lubricant film protects against rust and corrosion as long as it remains in place. However, after you shut down the motor for the day, gravity draws the oil back down into the oil sump, leaving components unprotected. The longer the engine sits, the more rust and corrosion can form.
Once rust begins to form, it doesn’t stop. It can slowly spread to the crankshaft journals, cylinder wall, piston rings and other areas. It acts like sandpaper and scours metal surfaces until engine failure eventually results. It can also prevent the piston rings from forming a good seal against the cylinder wall, which reduces compression and leads to power loss.
Aluminum parts may not rust, but they can corrode, especially in marine motors constantly exposed to humid air. If the valves aren’t completely sealed when the engine shuts down, damp air infiltrates the combustion chamber and causes aluminum pistons to corrode. Corrosion on the piston crown invites conditions that can lead to pre-ignition, a phenomenon where the fuel/air mixture ignites sporadically and potentially causes catastrophic engine failure.
Passenger car motor oils don’t cut it
It’s vital to use a motor oil formulated with anti-rust/anti-corrosion additives in vehicles and equipment that sit idle for long periods. These additives form a resilient protective layer that clings to engine parts for maximum protection. Since passenger cars/trucks are typically driven daily, rust and corrosion largely isn’t a concern. As such, most passenger car motor oils don’t contain sufficient rust and corrosion inhibitors for engines used periodically. Instead, use a motor oil specifically formulated for your application.
AMSOIL Synthetic Motorcycle Oil, AMSOIL marine engine oils, AMSOIL Z-ROD® Synthetic Motor Oil and AMSOIL Formula 4-Stroke® Synthetic Small Engine Oil contain robust rust and corrosion inhibitors. They deliver outstanding performance for your engines when you’re driving, and superior rust and corrosion protection when they sit idle.