Hello, New poster here. My emails to Mazda will explain below. I just brought my new 2009 Mazda 3 Value Touring 2.0L in for it's first oil change. I've been using synthetic oil since 1975 and I continue to do that. When they were done, I was surprised to see "XYZ" Mazda used Mobil 1 5-30w. I know the owners manual says to use 5-20w. The service manager told me they are now using 5-30w, both dino and synthetic in all new vehicles calling for 5-20w. He said because of the heat here in Florida they have had issues with the 5-20w. I asked if engine tolerances and warranty could be problems and he said absolutely not. Do you concur with your dealer on this issue? That was my question to Mazda, here is their answer: Thank you for your e-mail inquiry for correct oil. If your 2009 MAZDA3 has the 2.0L engine then the recommended oil would be the 5 w -20 and the manufacture would not recommend synthetic oils or a different weight oil, they have not be approved or tested. If any other oil is being used it could void warranty. If you have additional question please call me at xxx. Thank you, XXXXX Specialist, Customer Service My owners manual says nothing about NOT using synthetics. Thoughts anyone?