That is another benefit to synthetic. It is added insurance to protect from sludge. Some engines have turned out to be prone to sludge, Some Toyota's, Saabs, etc. Toyotas problem caused them to change their recommended oil change interval from 7500 mi to 5000 mi.


'90 Montero XLS (Sold, sadly)
'95 Montero LS 160k
'03 Montero Limited 30k