I stopped by the local Toyota dealer to ask the service manager if my warranty would be intact if a ran 5w20 synthetic instead of the 0w20 recommended in the manual. He told me no that only 5w20 dino oil can used and if I switched to synthetic I would have to use 0w20. I really cannot find a reason as to why I must use 0w20 especially considering the climate I live in.

 

look on the oil cap on mine it says to use 0w20 or 5w20, i use 0w-20 during the winter and 5w-20 on the summer

edit: also if you have high mileage on your engine don't switch to synthetic

 

The synthetic vs non isn't really an issue, but if it recommends 0w20 they can deny a warranty claim if they can prove that the "incorrect" oil blend caused a problem.

 

Toyota Dealer Oil that they use
5W20 Dino
0W20 Synthetic

From factory in the car
0W20 Synthetic

Note: Only once may 5W20 dino oil be used before switching back to 0W20 for the next oil change.

Your question is, if you provide your own synthetic 5W20 and do your own oil change will it violate the warranty? Not really with proof of purchase and proper oil change and filter use; but the recommendation is 0W20 Synthetic and it is more efficient in the engine for performance, consumption, and MPG.

So just use the 0W20. If you go to the dealer for the oil change 0W20 synth is what they will be using.

 

I just got a recent oil change from the dealer (had to pull some oil out again) and for my 09 they put in the dino 5W20.

I will be switching to Synthetic next oil change and debating i will probably put in 5W20 as well.

 

You can use either 0w-20 or 5w-20. 0w only comes as a synthetic. They recommend it due to the CAFE issues and supposedly better mileage. However, the cap says both and both are fine. If using 5w-20 then you can choose synthetic or dino or blend and there are entire websites debating the relative merits.

 

That's ridiculous. You can use synth oil in any of the recommended weights. They are totally compatible with dino oil. Even switching between synth and dino is not a problem with seals anymore. As long as you follow the recommended change intervals, your warranty is intact.
I have an 09 and I just changed the oil today to Synth.
Will follow the 2010 recommendation for oil changes every 10K miles.

 

Just use 5w20 synthetic and you'll be fine. 0w20 is hard to find and expensive. $7 a quart vs. $20 for a 5quart jug. Dealers are suppose to be going to full synthetic oil changes next year, and the price is going to be skyrocketing to $70 to get it done.