I see the new statement from Toyota Customer Service about using synthetic oil still states if you switch to synthetic oil, you should not switch back. I have tried repeatedly to get Toyota to say why this is recommended in their vehicles. I want to use Mobil 1 in my 2004 Sienna because I change my own oil most of the time. However, for those times I need an oil change and have to go to the dealer, they will most likely only use their conventional oil. I sure would like to know what the problem would be if I did this. Mobil 1 has long said their oil is compatible with all other conventional oils, and you can use both from time to time. Charles Ranheim
- posted
18 years ago