I notice a lot of people on this forum say 'change 3k miles or 3 months, whichever comes first', and a more than one year OCI is almost universally shunned among participants, even the AMSOIL freaks with their beloved 25000mile/1year warrantee.
Many posters would have you believe that if you drive a car even 500 miles a year, ie: a couple summer drives, you still shouldn't leave a group IV synthetic in for more than a year. (note I say Group IV, it has been said that some group V ester-based oils can be fairly hydroscopic)
What is the logic, if any, behind this? I can understand the logic behind the 3k mile/3 month, whichever comes first OCI is to implicitly compensate the interval for individuals who operate their vehicles with an inordinate number of cycles (leading to fuel contamination, soot buildup, etc. -- all the cons of running a cold engine). But for rarely driven vehicles, this advice would hardly seem appropriate.
After all, engines these days are sealed fairly tightly when sitting stationary, and unless exposed to a flood or leaking gaskets, water ingress is nearly impossible. Oil is naturally anti-corrossive and low oil acidity (low TAN/high TBN) keeps internal engine corrosion to a minimum. Synthetic oils do not suffer oxidative breakdown at all at normal atmospheric temperatures, so why then, do people still speak of such short time-based intervals on cars that are relatively rarely driven?
Many posters would have you believe that if you drive a car even 500 miles a year, ie: a couple summer drives, you still shouldn't leave a group IV synthetic in for more than a year. (note I say Group IV, it has been said that some group V ester-based oils can be fairly hydroscopic)
What is the logic, if any, behind this? I can understand the logic behind the 3k mile/3 month, whichever comes first OCI is to implicitly compensate the interval for individuals who operate their vehicles with an inordinate number of cycles (leading to fuel contamination, soot buildup, etc. -- all the cons of running a cold engine). But for rarely driven vehicles, this advice would hardly seem appropriate.
After all, engines these days are sealed fairly tightly when sitting stationary, and unless exposed to a flood or leaking gaskets, water ingress is nearly impossible. Oil is naturally anti-corrossive and low oil acidity (low TAN/high TBN) keeps internal engine corrosion to a minimum. Synthetic oils do not suffer oxidative breakdown at all at normal atmospheric temperatures, so why then, do people still speak of such short time-based intervals on cars that are relatively rarely driven?
