I use synthetic oil in my bike and change it often .
It has lots of life left in it but the bike oil filter is a bit primitive and does not filter too well .
When I drain the oil from the bike I then " re-use" it in the tractors and lawnmower etc .
Give your old oil to a [poor] farmer ,it's also good for lubricating slow moving chains on farm machinery .
Blessed are the cracked, for they let in the light. - Spike Milligan
"When you come to a fork in the road ,take it ! When you come to a spoon in the road ,take that also ."