That's just not true. Synthetic oil can be used in ANY engine as a replacement for conventional oil. Synthetic is superior to conventional oil and will protect your engine better. Also, you CAN extend oil changed with synthetic even driving under "severe service". Going 5000 to 7500 miles on synthetic is not a problem. I've converted all my Hyundai/KIAs to synthetic at 5000 miles and change the oil every 5000 miles.

 

If you use Amsoil you can change your oil once a year or every 15,000 miles. That's what I use on my cars and it's about $10 per quart but I end up saving a ton of money as I use a lot less oil and do a lot less oil changes.