I have a Suzuki c90t/1500.  It has 6000 miles.  I am about to get ready for the winter, and do the last oil change of the year.  I have two important questions:

1) can I start using synthetic?  If so, Which one?
2) does it really matter if I use motorcycle or car oil?  Is there a difference?

THANK YOU!  

HI; I have a C50T with 20,000 miles. I have used Mobil 1 sence the 600 mile service. I have had no problems. I was told that the automotive oil would affect the clutch. I have had no such problem. I just changed the oil it looked fine no shinny parts. I have adjusted the valves once at about 15K. The bike runs great.
I use mobil 1 cause that is what the parts store I do buisness with carries. The difference is with air cooled vers liquid cooled engines. The air cooled  oil uses different additives than the liquid cooled.
 I have not had any oil related trouble. The bike runs and gets good milage 45-50 mpg. Have a good day ... scruffy  

The common advice is to avoid oils that have "friction modifiers" or say "energy conserving" in the circular symbol. Supposedly, they can contribute to clutch slippage. I've never used used them in a bike, so I can't say if thats fact or fiction. For the most part, those oils are multigrade oils of 30W or lighter (??W30 or ??W20). I haven't yet seen a ??W40 that was labeled "energy conserving".

As for the breakin wear... At 6,000 miles, you've already worn off any high spots in the cylinders and bearing journals. It won't hurt the bike to go ahead and change to a synthetic, now.

Which synthetic or synthetic blend to use? That's a matter of personal preference. There are long arguements on many forums over which oil is better or worse than which other oil. I've never seen anything conclusive on the subject.

You *may* find that some synthetic oils will keep the oil galleries cleaner over the long run than some synthetic blends do. That's been argued too. If you're not planning on doing your own engine rebuilds, I doubt you'll see any practical difference.

I have never read of an engine failure that could be blamed on using the wrong brand of oil or using synthetic oil. Using the wrong weight of oil can cause problems.

regards,
Joe  

Yes, you can start using full synthetic pretty much right after your break in oil change. Any full synthetic is fine, I personally have used Mobil 1 and Amsoil with no problems.  If you plan on riding and using your bike during the winter, you're most likely going to want to use a 5w or 10w depending on how cold it is where you live. The colder, the lower the weight. Oil weight issues only arise when you use too thick of an oil at too low of a temp or vice versa.

DO NOT use car oil in your bike.  Car oil has friction modifiers which will cause your clutch to slip.