Keep in mind, the dealer uses whatever they get a good deal on. My mechanic is a 20 years Toyota Master and told me this. He's been in many dealerships.What would be considered too late to switch to synthetic. I was under the impression that the ISF used synthetic from the factory, but when I had the dealer do my 10,000 mile service yesterday, they put in conventional. Would switching to synthetic at my 15,000 mile oil change be too late? Thanks in advance.