I realize this post is a bit old but I have the same situation. Below is a copy of the e-mail that I received from ToyotaUSA concerning the exact same question. This person stated that a 10,000 oci in a Flex-Fuel vehicle would void the warranty, regardless of type of fuel used. It's probably 100% ok to do in practice, but it does give them a reason to deny a warranty claim...bummer!
Dear Mr. Edwards,
Thank you for contacting Toyota Motor Sales, U.S.A., Inc.
We appreciate your interest in the proper maintenance of your 2012 Tundra FFV.
Toyota can only recommend that you follow the maintenance recommendations given in your vehicle's Scheduled Maintenance Guide, which can be viewed online at http://www.toyota.com/t3Portal/docu...draFFV/pdf/2012_Toyota_Tundra_FFV_WMG_LR2.pdf.
Per this resource, Toyota recommends that you replace your engine oil and filter at every 5,000 miles or every 6 months, which ever comes first. If you will be using E85 fuel more than 50% of the time, oil and oil filter changes should occur at every 2,500 miles or every 3 months, which ever comes first. No separate recommendation is given for a Tundra FFV that is driven exclusively on gasoline, and repair to any potential damage that may result from observing a 10,000 mile oil change interval will not be covered by your Toyota factory warranties.
Please observe the 5,000 mile / 6 month recommendation given in your vehicle's Scheduled Maintenance Guide. Your first four or five scheduled maintenance services are complimentary under your Toyota Care coverage, depending on whether you reach 25,000 total miles before the vehicle is 2 years old. If you would like to discuss our maintenance recommendations in greater detail, please speak with your Toyota dealer's Service Advisors. As Toyota's technical experts in your neighborhood, your Service Advisors will be happy to discuss why we cannot recommend observing a 10,000 mile interval for replacement of your Tundra's engine oil.
Thank you for choosing Toyota for your driving needs. If we can be of further assistance, please feel free to contact us at Toyota Help.
Sincerely,
Alex Tiampo
Toyota Customer Experience
Dear Mr. Edwards,
Thank you for contacting Toyota Motor Sales, U.S.A., Inc.
We appreciate your interest in the proper maintenance of your 2012 Tundra FFV.
Toyota can only recommend that you follow the maintenance recommendations given in your vehicle's Scheduled Maintenance Guide, which can be viewed online at http://www.toyota.com/t3Portal/docu...draFFV/pdf/2012_Toyota_Tundra_FFV_WMG_LR2.pdf.
Per this resource, Toyota recommends that you replace your engine oil and filter at every 5,000 miles or every 6 months, which ever comes first. If you will be using E85 fuel more than 50% of the time, oil and oil filter changes should occur at every 2,500 miles or every 3 months, which ever comes first. No separate recommendation is given for a Tundra FFV that is driven exclusively on gasoline, and repair to any potential damage that may result from observing a 10,000 mile oil change interval will not be covered by your Toyota factory warranties.
Please observe the 5,000 mile / 6 month recommendation given in your vehicle's Scheduled Maintenance Guide. Your first four or five scheduled maintenance services are complimentary under your Toyota Care coverage, depending on whether you reach 25,000 total miles before the vehicle is 2 years old. If you would like to discuss our maintenance recommendations in greater detail, please speak with your Toyota dealer's Service Advisors. As Toyota's technical experts in your neighborhood, your Service Advisors will be happy to discuss why we cannot recommend observing a 10,000 mile interval for replacement of your Tundra's engine oil.
Thank you for choosing Toyota for your driving needs. If we can be of further assistance, please feel free to contact us at Toyota Help.
Sincerely,
Alex Tiampo
Toyota Customer Experience