I have a '97 1.8 T and thinking of using Mobil 1 10W-30 for the upcoming cold months here in the Northeast. I'm wondering though if this is problem if I currently use conventional oil (there's 27,000 on my odometer). Also, I was using Mobil 1 15W-50 during the summer of 1998 but switched back to conventional oil since then.

After using dino oils for long periods of time then switching to synthetics, some people experienced small oil leaks. I don't know if it's a good idea to keep switching back and forth between dino and synthetic. I would pick one route and stick with it. You can mix them if you want also, that may be a solution. FWIW, I'm in the Northeast, been using synthetic since 5K (currently 14K), now using Mobil 1 10W-30.