Dealers are plenty stupid. I had an Acura that called for 0W-20 (full synthetic and a little pricey). Manual said 5W-20 (semi-synthetic that is a lot cheaper) was ok as an interim oil if 0W-20 was not available but that you had to go back to 0W-20 on the next oil change.
Caught the dealer in a lie about the oil weight they use. They were doing 5W-20 on every oil change and charging the 0W-20 price. I was pretty sure this was the case, and I got photo evidence of it. Service manager was still a dìck about it - instead of acknowledging my complaint he told me I shouldn't have been back there
