If it has about 100k or less, I say run fully synthetic. I've been using Mobil 1 for years, but thinking of switching to Penzoil fully synthetic cause Mobil is a dirty oil. I've found if the engine hasn't been maintained or has high miles and has always had conventional oil run in it, changing it to synthetic may actually damage it. And if you were running synthetic and switch back to conventional, it may ruin the motor. Happened with my neighbor cause his buddy didn't tell him he ran synthetic.
