I want to share something I discovered about the oil viscosity in the 1.33-litre engine in my Toyota Yaris. I bought the car new from Hills of Woodford, along with some Toyota top-up oil, which was 5W-30 fully-synthetic. After the first service, I queried why it had been serviced with Toyota 0W-20 fully-synthetic rather than the 5W-30 that had been recommended when I bought the car a year before. All I was told was that Toyota had changed the specification.
Last year, I took over servicing the car myself and went to another Toyota dealer for engine oil, only to be supplied with Toyota 5W-30, which I queried with the dealer. A passing Toyota mechanic overheard my query and asked what I had been using. I said Toyota 0W-20 and he confirmed that it was the correct oil for that engine. I queried why it had changed and he said that it was because Toyota mechanics had been having to change the pistons regularly on engines run on 5W-30 due to excessive carbon build-up. Ian Wallace