Oil is the lifeblood of your engine, and it's extremely sensitive. Using clean, quality oil does wonders for the life and efficiency of your engine, but conversely, operating with dirty or degraded oil puts you at risk for hefty engine repair bills or even worse, a trip to the junkyard. While the engine manufacturer did most of the work to power your equipment, you're responsible for completing regularly scheduled oil changes to protect your engine and keep your lawn cut.
How engine oil works
Oil serves more than one purpose. For starters, oil's viscous, or slippery properties allow the tight-fitting, polished parts in an engine to slide past each other at thousands of revolutions per minute. By removing friction from those intricate moving parts, your engine uses less effort and operates more efficiently. Additionally, oil acts as a heat transfer. After cycling through the engine, it carries damaging heat away from those fast moving parts and into the sump where it cools before recycling.
Oil doesn't remain in the same condition as it was in the bottle. Besides heating to temperatures in excess of a brutal 200 degrees Fahrenheit, oil quality is compromised by oxidation and contact with moisture. Oxidation turns your oil to sludge, and warming and cooling across a broad range of temperatures allows condensation to form inside the engine, causing corrosion. So whereas an oil's viscosity or "rating of slipperiness" may have been 10W-30 (as an example) to start, it eventually degrades below the manufacturer's specification. The oil change intervals defined by the manufacturer in the engine manual are based on calculations of when the oil will deteriorate below its original condition.
Oil becomes contaminated
Unchanged air filters can wreak havoc on oil in one of two ways, if not a combination of both. If plugged, air finds other passages into the engine, allowing dust and dirt to enter the oil system, unfiltered. Or, the plugged air filter chokes the engine, making it consume more gasoline and dilute the oil.
Additionally, carbon, soot and acids produced during combustion and the shedding of tiny metallic shavings from friction between engine components all pollute the oil system. Depending on the quality of the oil filter, many of those impurities are caught, but only until the filter reaches capacity. After the filter is saturated, contaminants accumulate in the oil system where they remain until drained.
After the first 10 hours
Oil becomes extremely contaminated during its first hours of operation, or its "break-in" period. Certain engine components, though engineered and manufactured to precise tolerances, aren't a perfect fit. By design, the wall of a new engine cylinder has peaks; it's not perfectly smooth at a microscopic level. As the piston moves rapidly up and down that new cylinder, its rings file away the peaks into metallic shavings that deposit into the oil system until the end of the break-in period when the peaks become flattened. Using oil with a detergent will help lift those particles and allow them to drain from the system more easily.
Changing engine oil
You can't cheat physics. After a certain amount of use, engine oil deteriorates, becomes contaminated and requires changing. Whether you do it yourself or rely on one of numerous Ariens® or Gravely® service dealers to complete equipment maintenance, oil changes shouldn't be approached with a one-size-fits-all mentality. Engines of different sizes and manufacturers require different oil quantities, types, ratings and filters and should be performed at the intervals outlined in
your manual unless extra use dictates otherwise. Above all, make sure it gets done.