I guess I will ask the question here that nobody has, Why? No oil manufacture is recommending 75,000 mile changes. The longest is Amsoil at 30,000 miles, but for your conditions with a great deal of idling, they cut it to 15,000 miles. Why not keep the engine in good condition and sell that crate motor when you retire?
I think most people here are interested in how long they can extend their change intervals with no ill effects. Running an oil 75,000 miles does not do anything toward this cause. I have an idea, how about you run, Mobil 1 for 20,000 miles, no sampling and a filter change at 10,000 miles, drop it and replace with another synthetic, and do a UOA on the oil. Repeat this every 20,000 miles with a different synthetic. This would provide better information than the group than doing what amounts to abusing your vehicle.
Personally, I vote for Mobil 1 0w-40, and oil designed for extended changes in European cars. Second would be the Sweet Gummy bear stuff.
I think most people here are interested in how long they can extend their change intervals with no ill effects. Running an oil 75,000 miles does not do anything toward this cause. I have an idea, how about you run, Mobil 1 for 20,000 miles, no sampling and a filter change at 10,000 miles, drop it and replace with another synthetic, and do a UOA on the oil. Repeat this every 20,000 miles with a different synthetic. This would provide better information than the group than doing what amounts to abusing your vehicle.
Personally, I vote for Mobil 1 0w-40, and oil designed for extended changes in European cars. Second would be the Sweet Gummy bear stuff.