Just purchased a 2004 4runner for my wife. Has the 4.7, and 140000 miles. The vehicle looks great and, unfortuneatley, the PO never did a lick of maintanance. Original plugs, timing belt, etc. Ater $2400 at the local dealership,(didn't get taken, they basically did all required maint. plus changed out a leaky tranny seal, and chased down some nasty stereo wireing the PO did, which messed up a few other things like marker lights, license plate lights ets) I have a "new" runner with 140,000 break in miles. Would there be any potential issues going to a synthetic motor oil with this many miles on the engine? I have no way of knowing what oil the PO used, could have been synthetic for all I know.
Regards, Rick