I have a friend that is almost 100 years old.He changes his oil himself on his car,his garden tractor and his rototiller.His car has almost 100,000 miles.His garden tractor has in his opinion around 5,000 hrs cutting 5 acres of grass.Rototiller looks like it belonged to jesus it is so old.He has never had a engine related problem ever,so i asked him why.He replies is, i don,t use fancy oil indicators,or manuals telling me when to change my oil.I pull the dipstick run it through my fingers and if it looks like it is starting to get dirty it,s has to go.Luck is luck but a run of almost 100 years is a pretty good track record.Sometimes old school methods make alot of sense.No fancy gadjets allowed in his house. ( 2 men fishing one man says to the other man "my wife is an angle" the other man says your lucky my wife is still alive.)