Can I reuse lightly used oil when I change an oil filter?
This is more of an opinion based question rather than a &quot;how do I do this&quot; question.  Opinion based questions are discouraged here.  But I'm going to answer anyway and this is just my opinion.  The new oil got slightly contaminated by the old oil left in the filter. In the distant past it was a common practice to change the oil filter with every other oil change (cars and trucks) .  Some ppl did that, others replaced the filter every time. You should be fine re-using the drained oil with a new filter, but if you are really worried about, what is the cost of a the oil? It can't be too much for a lawn mower, so if it gives you peace of mind to get fresh oil and it only costs $10-$15, go for it.  That's pretty inexpensive to get peace of mind these days.