As mentioned, variable valve timing often requires oil flow thru tiny, intricate passages, which can easily become plugged from sludge build up, and can be extremely difficult to clean out. A few other things with "modern" vehicles that concern me, are no engine dipsticks, so you can`t check the oil level or visual condition, but have to rely on either an "oil condition monitor " system, or an often confusing in dash computer procedure, rubber belt driven oil pumps, that live in oil (who thought THAT was a good idea?), that can cause early deterioration of the rubber, plus the material can cause rubber dust/debris to clog up the oil pickup screen. Also, now some engines don`t use a positively driven oil pump, but rather have a variable displacement oil pump, which reduces oil pressure , I imagine to reduce parasitic horsepower drain, which just seems like a bad idea to me. To me, it seems like many of these "innovations" , to free up any small amount of power, can come at a high cost. Things like "Start/Stop" engines, that turn off at a traffic light, cylinder deactivation, direct EFI, water thin oils with long drain intervals, VVT, etc, will in the long run, cost much more to maintain and repair than the amount of gasoline they will save. Same goes for diesel engines with all the emissions crap that has been added the past 10-15 years.
