Red,
All motor oils contain detergency additives. This is nothing new. Synthetics do clean an engine better than standard oils, but it's not a problem. Years ago, standard oils left a lot more residue in engines than they do currently, and maybe the synthetics we had back then cleaned too well...anyway, back then folks thought that it was a problem. Now all the synthetic oil makers except maybe Amsoil say to just make the switch regardless of the mileage on your engine. Amsoil wants you to use their 15 minute engine flush (which I think is pretty ineffective). If you feel that your engine is heavily sludged and are concerned, a cleaning with Auto-Rx or Schaeffer's #131 Neutra is the best way to go.
I don't think that the term "semi-synthetic" has a standard meaning. Castrol Syntec is made from Group III base oils. That means that it's made from very highly refined petroleum. It does have the legal right to call itself fully synthetic, and it is good oil. Oil base stock fabricated from chemicals is called Group IV (polyaphaolephin...PAO) and Group V (other base oils including esters). These make better motor oil but cost more. The problem most of us have with GR-III oils is that they're priced the same as true synthetics and don't perform as well. If the price is proportional with the quality of the oil, and the consumer understands just what this oil will do and won't do, GR-III synthetics are an OK deal.
Ken
[ February 05, 2003, 01:46 PM: Message edited by: Ken2 ]