On a Toyota forum, I found what is supposedly an official response from Toyota Corporate to an owner who questioned them about using synthetic oil. Their response, which is basically a canned company-policy reply, did not surprise me.
However, they do make a statement about once you begin using a syn oil, you should not switch back and forth with dino. Is there any merit at all to this view?
Here is the reply:
Thank you for contacting Toyota Motor Sales, U.S.A., Inc.
We appreciate your inquiry regarding the us of synthetic oil in your 4Runner.
All Toyota vehicles come from the factory with natural petroleum-based engine oil. Toyota is currently recommending American Petroleum Institute (API) grade SJ petroleum-based engine oil. In moderate climates, this oil should have a Society of Automotive Engineers (SAE) viscosity rating of 5W-30. In our high mileage tests with preventative maintenance performed at the recommended intervals, the recommended natural petroleum-based oil has provided excellent service.
If you decide to use synthetic oil for the engine, it would be best not to switch until the first scheduled oil change. Synthetic oil should meet or exceed the above specifications. Even if synthetic oil is used, we do not recommend a longer oil change interval. Also, once synthetic oil is used, you should keep using it and not switch back and forth with natural petroleum-based oil.
If the engine oil that you use, whether natural or synthetic, does not meet the above specifications or is defective, any resulting damage to the engine will not be covered by the Toyota New Vehicle Limited Warranty. You can protect yourself against this possibility by having your maintenance services performed by a factory-authorized Toyota dealer.
The Scheduled Maintenance Guide cites the minimum recommended services under what is assumed to be a standard, or typical set of driving conditions. In terms of maintaining the integrity of your warranty, our recommendation is adherence to the Scheduled Maintenance guide, which recommends service intervals of every 5000 miles, or 6 months, whichever comes first.
According to our records, the 4Runner we have on file for your is V8 4.7 4WD . The oil capacity for that engine, with a filter, is 6.5 quarts.
Your email has been documented at our National Headquarters under file #200412021090. If we can be of further assistance, please feel free to contact us.
National Customer Relations