Seeing it's the first time in 5yrs, I'd run it for a short time then drain all the oil, change the filter & refill with clean oil - oil is relatively cheap so it's a false economy to try to save a few $'s - use something like an icecream container to position/ catch the waste oil under the drain plug & filter.
Further things to consider :
- IMO on mowers oil should be changed every 50hrs or so, or at the end of each season (whichever comes first)
- Clean &/or replace the air filter at the same schedule
- Drain the old oil when the motor is warm as it better flows/removes the contaminants (just be cautious not to burn you hands if it's too hot)
- Next when removing the oil filter make certain the rubber sealing ring/gasket remains on & is removed with the oil filter (& doesn't stay on the engine oil filter housing)
- When installing a new oil filter place a thin layer/smear of oil onto the rubber sealing ring/gasket on the new oil filter & the same with the filter thread
- Then use quality oil & a suitable grade recommended for the engine, make certain to use the correct volume taking care not to under nor over fill (check the marking on the dipstick once you fill, then in a few hours, shortly after starting post an oil change & then prior to every use))
- Invest in a rubber strap oil filter wrench (for a few $ it'll make the job of removing/installing the oil filter easy, but be carefull not to overtighten a new filter, spin it on hand tight then max 1/8 turn with the wrench - it should be firm, not reefed up tight with all your strength)
Same principles/process apply for engine oil changes for most equipment, vehicles, motorcycles....etc.
:thumbsup:Congratulations to all who have an enquiring mind, ask these type of questions & are willing to learn - mechanical skills are acquired rather than inherited (apart from saving the cost of workshop rates I'm surprised more people don't do their own basic maintenace if only for the feeling of accomplishment )