GM-GMC: OIL, mobile 1 synthetic oil, toyota camry

Question
Hi,

  I bought a used 2002 GMC truck. It's a 4x4 with extra cab 4 door with the 4.8 litre engine.
It runs fine and I'm very happy with it.
I'm thinking about useing Mobile 1 synthetic oil.
Is this a good idea? A friend of mine told me once you use this kind of oil, you should never go back to regular oil.

Also, My girlfriend has a 1999 toyota camry.  It has high miles and is starting to burn a little smoke at start up. I also was thinking about useing Mobil 1 in her car but I'm a little scared
after what my friend told me.

Is it safe to use this oil in both our cars? and, will it hurt if I change back to regular oil?

Thanks for any help you can give...
Jim
Jjasmin63@aol.com

Answer
Early on, Mobil 1 and other synthetics could cause seal problems and leaks.

If your engine is not leaking oil, Mobil 1 is a very good choice for ultimate protection and economy.  I use Mobil 1 10W-30 in two 1985 Toyota MR2s that I own.  Both have more than 150,000 miles on them.

You can switch back to regular oil without any issues, should you choose to do so.  However, do not mix synthetic and non-synthetic oils.

You will notice engine performance improvements if you switch to synthetic oil but the best reason is that the synthetics can handle the high engine temperatures of today's engines better than regular oil.