Whereas I've always done the oil changes on my truck, my wife would usually take her car to the dealership or Quickie Lube to get an oil change. She drives an '05 Grand Am with a V6 and about 96,000 miles. I went with a 5w-30 PP and a slightly oversize Fleetguard LF3554 filter. I'm hoping the synthetic oil will help clean out the engine a little and that I'll be able to do a longer drain interval. How long a drain interval do you think I could manage safely?