So far NOT ONE car that has been properly maintained has had > sludge...I > stand by the statement... > [Sluge has been repeatedly found in some motors that have been > properly > maintained; that is the point of the warranty extention issued > by Toyota and > others]. >

Sludge is caused by not changing your oil. > [This is not a logical statement. Sludge is created when > various > contaminants, in the presence of water, can no longer be > nutralized and held > in suspension by the oil. Some motors under some use > conditons can go a > very very long time without the motor experiencing sludge > formation. It is > circular reasoning to say it is caused by not changing your > oil. One needs > to change the oil just before the oil's ability to nutralize > the acids and > hold the solids in suspension is lost. Most Americans tend to > change the oil > too frequently under this criteria]. >  >> > Normal varnish is to be expected. This is a golden browning, > like the color of toast, but its only a discoloration, not a > build up of > sludge and in normal and unavoidable. > [Varnish is formed by the exposure of certain compounds > (usually associated > with viscosity index improvers) to air and heat. Avoiding > multi-viscosity > oils that use excessive amounts of viscosity index improver is > the best way > to avoid varnish formation. It is avoidable and excess varnish > formation can > cause stuck and even cracked rings.] >

A properly formulate synthetic tends to use a lot less > viscosity index > improver additives, and tends to do a much better job at > forming coke, > neutralizing acids, holding solids in suspension, and > marinating stable > viscosity over time. If you change your oil ever 2,500 miles > your motor will > not demand those improved characteristics; except possibly > better cold > weather flow characteristics. >

Richard.