crawfjh...That was my concern also, living in Arizona where the temps in July and August are normally between 105-112 degress, plus I pull a 3000lbs boat or a 5000lbs travel trailer. I spoke with a rep from Toyota this past weekend, plus a Toyota mechanic who just returned from a class on the 5.7, and they both said use only the oil recommended in the Owners Manual. I also sent an E-mail to Toyota asking the same question...here is their answer:
Subject
5.7L V8 Oil Viscosity
Discussion Thread
Response (Jonathan) 04/16/2007 01:44 PM
Thank you for contacting Toyota Motor Sales, U.S.A., Inc.
We appreciate the opportunity to address your inquiry.
All Toyota vehicles come from the factory with natural petroleum-based engine oil. Toyota is currently recommending for the 2007 Tundra with the 5.7 Liter engine, 5W-20 or 0W-20. With preventative maintenance performed at the recommended intervals, the recommended natural petroleum-based oil has provided excellent service under the conditions you have inquired about.
We do not recommend deviating from the recommended oil viscosity for this vehicle.
Your email has been documented at our National Headquarters under file #200704161293. If we can be of further assistance, please feel free to contact us.
Jonathan Paez Toyota Customer Experience
Customer 04/13/2007 11:06 AM
I am researching the Toyota Tundra, 5.7L, SR-5. From the information I have gathered from the Toyota.com website, it seems the Owners Manual recommends either a Ow-20w or 5w-20w oil for that engine. The viscosity seems very low. I live in Arizona where the summer temps often reach 115-120 degrees. Is the 5w-20w oil still recommended for those temps, even when pulling a 5000lbs trailer?? Thanks!