In my 66 I use Kendall GT-1 straight 40, in my Z06 I use Mobil 1 10w30, and in wifes Envoy I use Mobil 1 10w30.
I have always felt that changing your oil is an inexpensive way to prolong and take care of the heart of any car. After working at dealerships for 30 plus years I have seen the results from changing and not changing your oil on a regular basis. With Toyota V-6 engines it is extremely critical that the motor oil is changed frequently because for some reason the seem to be prone to sludge buildup. I recall one customer who never changed his oil in 20,000 miles on a V-6 Camry and he took a trip to North Carolina from Mass. He used 17 quarts of oil in his roundtrip and when the car came in the crankcase was almost empty. The car had the original oil filter on it and when we removed it it must have weighed 2 pounds. We pulled the valve covers and the burnt sledge was like nothing I have ever witnessed. Even the block webbing for the crank was brown where the oil had been burnt in. Toyota wouldn't warranty the motor, the only time I ever saw them refuse to do so.
As far as Mobil 5000 and 7500 oil goes I believe the 5000 is a conventional oil not a synthetic, and the 7500 is a mixture of synthetic and conventional, neither is the same as Mobil 1, a pure synthetic. Mobil 1 Extended is suppose to be good for up to 15,000 miles between changes. To be honest I have always been skeptical of any product that is new and improved especially when they give some kind of special guarantee. I have never heard of anyone taking an oil company to task to make good on their special guarantees, I think that all that mumbo jumbo is designed to target people who are not so savvy when it comes to vehicle maintainance, it's just a new spin to entice people to buy their new redesigned product.
Some people say that when you get a new car it is not necessary to change your oil early. I disagree. A new engine is very tight as far a clearances go as opposed to an engine that has lets say 10,000 miles on it. Tighter clearances mean more friction, more friction means more heat, more heat means the oil breaks down faster. Also a new engine creates filings in the oil from breakin. The longer you run the breakin oil the more those filings are being washed thru your main, rod and cam bearings. Most high performance cam manufactures recommend that when you install a new cam and lifters in your motor that upon first startup you run the motor for 20 minutes at about 2000 rpm to break in the new cam and lifters, then change the oil and filter to get rid of any filings. When I got my Z06 I picked it up in New Jersey and drove it back to Mass, 472 miles. Next morning I changed the oil and filter. When I emptied the drain pan before it was completely empty I took my finger and dipped it in the oil and let the sun shine on my fingertip, sure enough there were plenty of tiny tiny filings glistening in the sun on my fingertip. I changed the oil again at 1000 miles. Some people even suggest that Mobil 1 is to slippery for a new engine to break in properly and recommend draining it and replacing it with conventional for the break in period. Any good engine builder will tell you the importance of changing your oil. Hell when I bought my John Deer tractor I changed the oil after the first use and after 10 hours I switched to Mobil one. Sure if your going to keep the car for a year or two why bother, but if your in for the long haul oil changes will definitely prolong the life of your engine.
Moral of this long winded reply is this, oil is cheap, six quarts at Costco is $27.00, $6.00 for a filter and hell it's fun to do. I change the oil on all three of my vehicles and use GM brand oil filters, and in 35 years of street racing, racing on dragstrips, hundreds of thousands of miles driving, knock on wood I have never experienced and engine or tranny failure. Even when I worked at dealerships, having hundreds of demos, when the salesman would call up the maintenance records for the potential buyers, my demos would always have been serviced regularly, especially oil changes. It just makes sense.
