quote:Originally posted by Buster:
Kirk, Grp III's have better solvency than Group IV's, but you give up a little volatility.
Those Group III's need the extra solvency to clean up some of the sludge/varnish that they are still to prone to creating. Group III oils were also used in some of those sludge monster cars,while group IV oils did a much better job in said engines. I recall reading many articles where motorists had sludge damaged engines with the M1(group III oils),and other group III synthetics that failed,where group IV held up!
Remember,Group IV's don't typically sludge,so solvency is not really needed.
Group III oils if you burn them will cause some varnish,while the group IV oils do not.
Another interesting phenomenon is that well formulated group IV motor oils seem to still clean an engine that is sludged/varnished.
Group IV oils have solvent like properties without actually having any direct solvents making them passively clean the engine,but more importantly.......KEEP THE ENGINE CLEAN IN THE FIRST PLACE.
This is a Noria link discussing solvency.......
http://www.machinerylubricatio...synthetic-oil-choice
"For example, there have been numerous studies showing that the poor solvency of certain types of petroleum-based synthetics (and for that matter, highly refined mineral oils) can result in a greater tendency to lay down varnish in high-temperature applications such as gas turbines because the oil does not have the solvency to keep the oil-wetted components clean."