How's this for an oil change interval - two years now, and counting on Amsoil........I just changed my full flow and bypass filter. This is on my truck, not the 4-runner, by the way. My last oil analysis says it's still good, will probably need to be changed the the 2 1/2 year mark, but I will do it this spring when I service the wife's ride. I pulled the dipstick the other day while filling up and the oil is still a dark honey color.
I was also wondering about the owners who had claims of sludge running Amsoil at extended drain intervals. I've never seen or heard of sludge running full synthetic. In fact, not getting sludge is one of the main benefits of running synthetic oil. My truck has almost 100,000 miles racked up, with only 3 oil changes in it's life, and when I had the pan and heads off (for mods mind you, not repairs), I couldn't find even a trace of sludge. And this is on a BOMBed diesel. If you know anything about diesel, There is an inheirent amount of soot that comes with the combustion process, and the oil is subjected heavily to the effects of the combustion byproducts. Good quality synthetic oil is built with addative packages designed to handle this contamination until it can rid itself of it during filtration. Same goes for what are normally sludge causing contaminants found in both diesel and gas engines. Amsoil's drain interval of 1yr./25,000 miles is based on normal service, ie., mainly highway miles. For severe service, such as stop and go city driving, they recommend a 15, 000 mile drain interval. I'm guessing if sludge was formed in an engine full of synthetic Amsoil, that it was driven past it's ability to handle contaminants any longer, and at that point, Amsoil is within it's right to deny any such warranty coverage. In my opinion, if you are going to push past the severe service interval, you should have an oil analysis done at that point to make sure you can do so without harm.