On Wed, 29 Apr 2009 15:34:03 -0700, SMS    
   wrote:   
      
   >clare@snyder.on.ca wrote:   
   >   
   >>  You can leave oil in YOUR car as long as you want. I'll change mine   
   >> every 5000 miles.   
   >   
   >That's great. Just don't change it every 3000 miles, with synthetic base   
   >stock or petroleum base stock, and think that it's providing an iota of   
   >benefit versus 5000 mile changes. It may make someone feel good to   
   >change their oil more often than necessary (recreational oil changing)   
   >but it doesn't do anything for the engine. Period.   
   >   
   >I've measured the compression on vehicles I've had for 10 years and 13   
   >years with 5K oil changes on dino oil and they've been close to the top   
   >end of the range of compression.   
      
   The compression may be perfect (or even higher than normal) and the   
   engine may still be severely damaged. Carbon buildup due to oil   
   consumption can increase compression significantly - enough to hide   
   the effect of both bad rings and bad valves in extreme cases.   
      
   Add to that the fact that bearing wear does not affect compression -   
   and even camshaft wear will often not give any indication of trouble   
   on a cranking speed compression test. The current "coking" issues will   
   not necessarily affect compression before the engine fails.   
   >You make it sound like an 18 year old engine that still runs is some   
   >sort of anomaly, but it's not. Engines that fail usually do so because   
   >they are run without oil or without coolant, or because of a design flaw   
   >(i.e. the Saturn engines that were prone to head cracking). Not because   
   >the oil was changed at 5000 miles versus 3000 miles, and unrelated to   
   >the base stock of the oil.   
      
   What percentage of vehicles sold 18 years ago are still on the road?   
   What percentage of those sold TODAY will still be on the road in 18   
   years?   
   Want to bet it will be those that were maintained?   
   The failure of Chrysler, Honda, and Toyota engines due to "sludge" or   
   "coking" can be 100% prevented by changing the oil often enough and   
   running premium quality (usually this means synthetic - but some dyno   
   or synth blends also qualify) engine oil.   
   And depending on the driving conditions, 3000 miles MIGHT be the   
   required interval (low mileage, short trips, temperature extremes,   
   etc) with a standard oil.. The additive package used by the refiner is   
   at least as important as the base stock - but that is not to say a   
   synthetic base may not be advantageous.   
      
   I think it is safe to say that GENERALLY an engine that fails fails   
   for one of 2 reasons. Neglect or design.   
   The odd one dies of "old age" at extremely high mileage due to wear   
   and fatigue, in spite of exemplary maintenance and superior design.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)