Visa free travel to Shanghai

Hello - I am an American passport holder currently in China on a 90 day, double entry tourist visa. My entry into China counted as one entry and my trip to and from Hong Kong counted as another.  I want to travel to Thailand and back to China to catch my return trip back to the US 1 day later.  

I have an electronic ticket.  Can I show my print out from the airline at PVG immigration?

Also, I won't have a valid visa when I check-in at BKK. Usually they check to make sure I have a proper visa.  What happens in BKK?

Citizens of some countries can stay in Shanghai for up to 48 hours if they're transiting through the Pudong Airport or Hongqiao Airport to to move on to a third country. As an U.S. citizen you should be able to do this. You still need to go through immigration checkpoint and they'll put a special stamp on your passport. Make sure you have your itinerary, valid passport and your plane ticket for flying out. You still need to fill out a form (arrival? departure? not sure which one); bring the form/forms with you to the counter, otherwise you'll have to leave to leave the line to get one.

People reported in the past that, with an electronic tickets, they needed to present their invoices that show additional information about your tickets - they were paid for, how payments were made, etc.

As for Thailand, U.S. citizens can stay in the country for up to 30 days with no visa (if they arrive by air; 15 days if they arrive by land). The visa-free stay cannot exceed 90s within a period of six months (you kow, get in and out and in again). And passort must be valid for six months beyond arrival date.

Some travelers in the past reported that they had to do some talking to convince their air carrier to let them board plane going to China without a visa. One'd think that nowadays most airlines know about China's Shanghai transit policy.