In 1980 I had a 78 --280Z . Penzoil was advertising a 7500 mile oil and STP was advertising a 15000 mile double oil filter. I tried both and at around 5400 miles my oil pressure dropped off by 50% at idle. I tried it again and met with the same results. One or both of them were giving up.

I have a friend who use to drain the synthetic oil out of his race car and put in in his 4 cylinder S 10 pickup. He drove that S10 over 300,000 miles and claims he never changed the oil more than 10 times. He would however, change the filter from time to time.

Mobil 1 has recently started advertising their 5000 mile synthetic oil. I have beeen using the old mobil 1 and the Purolator,pure one oil filter for years and running 5000 miles on the oil change . My Camry LE has 57000 miles and looks and runs like new . My 92 GMC pickup has 168000 miles, runs perfect, burns no oil,and gets 19 MPG.

I believe there have been test to prove that some of these synthetics loose absolutely no lubricating qualities at 3000 miles.

The oil companies dont want you to know that. They want to sell oil.