Lawn Mower Oil Change


If you don't do anything else to prolong the life and happiness of your small engines (and your automobile, for that matter) it should be an oil change at the recommended interval. Oil loses its lubrication and cooling effectiveness with use and this will gradually take its toll on your precision engine parts. Even a simple lawn mower engine is machined to very precise tolerances and any contamination will increase wear. Ultimately, its performance - starting and running - will suffer and its life will be shortened.

Since there is typically no oil filter, all the grit, metal particles, and other undesirable stuff continues to circulate with the oil to find its way in between precision engine parts.

For small engines, the oil change interval is usually specified to be about 25 hours of use. More frequent oil changes may be desirable if the equipment is operated in an extremely dusty environment.

A typical mowing season for a modest size lot is around this amount of time so an oil change once a season is probably satisfactory. I recommend this be done at the end of the season so that the old contaminated oil does not sit in the crankcase during the winter months and you will not (conveniently) forget to do this at the beginning of next season when you are eager to get at that straggly lawn.

An oil change isn't really a big deal

The oil change procedure is a lot simpler than for an automobile as everything is readily accessible and there is no oil filter to worry about.
  • You will need a funnel, low wide container or drain pan for the used oil, and a container like a plastic milk jug for temporary storage of the used oil for disposal.

  • Spread adequate newspaper on the ground to collect any drippings.

  • Run the mower for about 2 to 3 minutes to allow the oil to circulate and warm up so that it is less viscous and will flow more easily. Stop the mower and remove the spark plug wire.

  • If the fuel tank is less than about 1/3 full, then you will probably not have any problems, otherwise you will have to drain some gas or remove the fuel tank so that gas does not spill out of the breather hole in the cap.

  • If there is an oil drain plug, you can use this to drain the oil. However, it is usually more convenient to just turn the mower on its side, carburetor side up. This is usually acceptable for the short time that will be involved. Immediately check for any oil leakage - if there is any, we will need to avoid tipping the mower as much - look for the drain plug.

  • Wipe around the oil filler cap with a clean cloth or paper towel to remove the dirt and grime that has likely collected there. The oil filler will either be on or near the bottom of the engine or at the top of the shroud (Eager 1 type). If it is not right at the bottom, there will be a dipstick attached to it.

  • Place your wide mouthed drain pan under the oil filler cap and remove the cap. The oil will flow into your pan. Let it continue until the dripping stops - probably 10 minutes or so.

  • Set the mower upright on a level surface. Wipe any drips on the engine and deck up with a clean rag or paper towel.

  • Use the recommended oil for your engine. SAE30 is usually specified by the engine manufacturer but they will usually state that 10W-30 or 10W-40 (SG rating) are acceptable substitutes. These 'multi-weight' oils are widely available and inexpensive. Typical small engine oil capacity is just over 1/2 quart. Start low and incrementally add oil until just below full on the dipstick or at the top of the oil fill hole if there is no dipstick. DO NOT overfill. Give it time for the relatively viscous oil to find its way into the crankcase. Tipping the mower back and forth a bit will help this process.

  • Replace the filler cap. Wipe up any additional drips.

  • Replace the spark plug wire. Then, start and run the engine for a couple of minutes. Wait a few minutes, then recheck the level. Top it off if needed.

  • Transfer the used oil from your drain pan to the storage container and dispose of it in an environmentally safe manner.