Rust is very harmful to engine durability in a variety of ways. Most people think of rust as the typical brownish coloration (barnyard rust) often found on ferrous- containing (iron) components which have been exposed to the elements. That is only one small part of the problem.
A more accurate term for what most people know as rust is corrosion. Corrosion can exist in many forms, and one of those forms is barnyard rust. Corrosion occurs any time a surface is left unprotected, and the metal on the surface is allowed to combine with oxygen (oxidation). Oxygen in the air (or water) combines with the metal to form a fairly coarse abrasive material.
Rust occurs particularly quickly if an unprotected surface comes in contact with water and chlorine or sulfur. The chlorine or sulfur combine with the water to form hydrochloric or sulfuric acid, and it quickly attacks the metal surface. That’s why all good lube oil formulations are basic – to help prevent corrosive wear. In modern day engines corrosive wear is usually more prevalent than abrasive wear.
Iron rust is abrasive, and it can play havoc with cylinder and valve train wear accelerating it by a factor of 2 or 3. Highly stressed areas, such as push rod ends and valve springs are particularly susceptible. But iron rust isn’t nearly as abrasive as aluminum corrosion. (Aluminum oxide is used on grinding wheels.) If aluminum corrosion gets into critical clearance areas such as cylinders or the valve train, it can actually cause engines to fail.
Rust inside an assembled engine or transmission can occur any time the oil is allowed to drain off a component due to infrequent use. Engines which are operated daily or weekly seldom encounter this problem, but many street rods, muscle cars, and race cars are often stored for several months without being turned over or fired up. This is a recipe for rusting problems.
Water and low temperatures significantly increase the propensity to rust. Engines fired up infrequently generate a tremendous amount of condensation. If the engine isn’t allowed to completely warm up, this condensation remains inside the engine. (Water will not burn off until the internal engine temperature (oil temperature) reaches 212 degrees F.) This water will then attack any surface which isn’t adequately protected by either an oil film or a vapor phase rust inhibitor ( new tools which often contain a packet of vapor phase rust inhibitor to prevent rusting in shipping and storage).
The recent trend of using ethanol in gasoline fuels increases rusting tendencies significantly since alcohols have a tremendous affinity for water. In other words, alcohol, whether it is ethanol or methanol, acts like a sponge to gather up any free water in the area. Any unburned alcohol in your engine will soon be fully saturated with water. That’s why racers never leave alcohol containers open to the atmosphere. Open containers must be thrown away because they will contain significant water after only a brief period of time.
Military vehicles often sit unattended for extended periods. The military lost so many engines due to rust problems that they came to the major specialty chemical (additive) manufacturers for a solution. A 500-hour humidity cabinet rust test was developed to both accelerate and replicate the problems the military were experiencing in the field (even in desert climates).
Today the military demand that all engine oils supplied to them must pass the 500-hour humidity cabinet rust test. When the Driven Hot Rod Oil was developed, street rodders requested protection against rust for vehicles which are often stored for months (even years). Additive chemistry which allowed the Hot Rod Oils to pass the 500-hour humidity cabinet rust test was incorporated into all of the Driven Hot Rod Oils.
No other commercial engine oils on the market contain this chemistry.