Here is an excellent article, by someone who knows, on oil, filters, antifreeze and gear lube. What he says is why I WILL and AM using synthetic oils. http://www.boss302.com/oil.htm

Synthetics are superior to conventional oils, more so when it comes to service interval length. However sometimes the extra cost just can't be justified. A Cummins 5.9 could probably run lard in the crankcase for 400k miles lol, so picking a certain brand is not as important as some have said.

Like myself I'm also running petroleum based lubes in everything and pulling 21-23 MPG which happens to be highier than most... So why waste the extra money on Synthetics when I'm beating most rigs that use it... :confused: LOL