I really would be careful about the Amsoil 25K marketing hype, as they have provided no real evidence that their oil lasts any longer than other major brand fully synthetics and if you blow your engine up due to too long an OCI, I bet the fine print in the terms and conditions means they are not liable.
In general terms a fully synthetic oil might be OK for a 50% extension to the OCI of a dino oil, but contamination still effects both oil types, so the idea that Amsoil have of encouraging a 25K OCI is nuts, particularly for an older engine or one in severe service type use.
Extending a normal OCI is only safe if you are doing UOA at regular intervals to see what is happening.
Originally Posted By: Donald
I think the best oil for the money is PP at Walmart. Easy to get, decent price, excellent oil.
If you wanted to do 25K mile oil changes, then Amsoil is the only one.
As far as gear oil or ATF, I think Amsoil is the best and worth the expense of ordering it online and paying for shipping. While many people change their own oil, few change their own ATF or gear oil as evidence of what is on the Walmart shelf. Tons of motor oil and only a little ATF and gear oil.