Every car I've switched to Amsoil I've noticed upon start-up, the tach revs to a slightly higher RPM for idle then comes down to the normal idle RPM. I'm assuming it is because the engine parts are moving much easier with synthetic lubrication.

I've read that synthetic oils were created by the Nazis in WWII. With the Allies bombing their oil production facilities into oblivion, they were forced to come up with an oil substitute. Abandoned German tanks filled with synthetic oil were found 40 years later and the engines started right up!!!

Years back I took a tour of a Helicopter maintenance facility belonging to the Air National Guard. If memory serves me right, the maintenance guy showed me the ins and outs of a Black Hawk helicopter. He said each turbine jet engine costs $750,000. He said they ran them on synthetic oil and NEVER changed the oil. I figure if it is good enough for $750,000 jet turbines,, it is good enough for my thirty year old diesel!!!