I've always used 5W30 Mobil 1.  Just this past weekend I changed to 10W30 because I can get it much cheaper at a wholesale store then the local parts store.

So I haven't noticed any difference or leaks.

I love the synthetic, I think it's worth every cent.  My motor runs smoother, cooler and more powerful.  Also, my Sidekick stays outside year round, and it when it's -40 degress C outside, that motor oil runs silky smooth.

Castrol Syntec is a few bucks cheaper and alot of Japanese race cars run on it so I say go for it!!!

This is kind of a dumb question, but is Castrol Syntec a partial synthetic, or full synthetic.  I thought that Castrol made a partial synthetic, but I can't remember.  Anybody know about this  Thanks, Dave

This is kind of a dumb question, but is Castrol Syntec a partial synthetic, or full synthetic.  I thought that Castrol made a partial synthetic, but I can't remember.  Anybody know about this  Thanks, Dave

0w30 (German Castrol) is real synthetic, the rest are not truly synthetic. Still good oil.

if you run synthetic can you go back to regulor oil?  

if you run synthetic can you go back to regulor oil?  

Yes and you can even mix if you have too. A few years ago this was not possible, but the polymers in the syn oil have come a long way.
They used to sludge up when you mixed in dino oil.

Well, thats good to know, I wasn't sure if Syntec was all synthetic, like say, Mobil one.  Thanks, for the info, Dave

It's a hydrocracked Group III. Castrol had a court battle to prove it was synthetic. They won, we lost, it's still not a true synthetic. I like Castrol products, it's their marketing that leaves something to be desired.