Terry G,
Your question was;
Isnt it true that engine contaminants affect
synthetics the same way they affect the
petroleum based oils and that it would be
more cost effective to buy the cheaper oils
and just change more often?
An oil, synthetic or petro, costly or cheep has to incounter the same comtaminants in the engine. (talking about diesel engines) This part of your question is true, however how an oil handles the comtaminants is the key to how much or how little wear happens, or how long an oil can handle soot before it can't handle it anymore and starts to develop deposits or build up soot that developes into bigger particles and starts to wear on you cylinder walls.
The answer is not all oils are made the same. you can buy a cheep oil and change it often and you still get the higher specific wear rate then you would if you used a high quality oil, weather it be synthetic or petroleum. For instance an oil that uses mostly calcium and not very much Magnesium is not a long drain oil and if you tryed to go longer oil drains you would end up with higher wear rates and soot buildup etc. But if you use an oil that was made for longer oil drains like LE or Amsoil and others etc. that have a lot of magneisum and don't rely so much on the cheep Calcium (Calcium and Magnesium do the same thing degergent/dispersant) then you can rest assured that the oil will go long drains without higher wear. You can buy cheep oil and you will always have a cheep oil in your $10,000 engine or you can spend a little more and have the best protection $ can buy. I believe that anyone that is in the oil business selling petroleum or synthetic high quality or cheep will agree that there are oils out there that will last longer and reduce wear better than a cheep oil.
I'll use Amsoil and LE for examples because they are the most talked about on this sight. Both Amsoil and LE have engines that have gone 100,000 miles without draining the oil. These same engines have gone over 1,000,000 miles with no overhauls. Knowing this and knowing how much the oil cost compairison is between say LE and regular oil about 3 times mor for LE you would only have to go 3 times longer for the oil to pay for itself. Since a lot ot guys only go 3,000 miles before changing oil that would only be 9,000 miles. Also keep in mind that we see 3 to 7% fuel savings using LE over regular oils (does fuel cost mean anything today???) Figure that into the equation and which one is more expensive now? Recently a comparison was done with a 8. 2L Detroit diesel engine in a school bus that was going 6,000 miles on an oil change using a major brand diesel oil talked about a lot on this sight. They switched to LE and that same engine went 25,700 miles without an oil change. The wear ppm per mile were recuced by; irom down 82%, copper down by 88% and lead down by 91%. Fuel soot was reduced by 76%, the viscosity was maintined in the middle of the SAE 40 range and the TBN is still high. I've used high quality oil for over 21 years and will never go back to cheep oil.
Sincerely, Kevin
Both oils drains were extablished by using oil analysis.
Attention: TDR Forum Junkies 
