[MindBomber]

I'm sure the manager is quite aware the 370z is spec'd for a full-syn or a syn blend, but had over riding reasons to want it changed with dino and doesn't feel the need to explain them to an apprentice. My guess would be the profit margin on dino oil is higher and therefore using it in a car built by another manufacturer is preferable. It's not really a big deal, running dino in most cars spec'd for syn isn't going to result in catastrophic failure. It's just like how someone mentioned Dueck GM uses 87 octane in every car on its lot, even if it's spec'd for 91 octane.

Speaking as someone who managed a group of trades apprentices your age for years;

in this scenario, I would have had the identical reaction;
if you brought it up again, I'd probably fire you (ie. spec sheet from Nissan);
if you brought it up to my boss, he'd say your responsibility is to listen to me and you'd be on thin ice with him too.

Enthusiasm, wanting to learn, a willingness to take on added responsibility; those are good qualities to demonstrate when you're at the bottom of the ladder. Asking a question is a good way to demonstrate those qualities. Contradicting your boss and allowing a customer to witness that to some degree (which sounds like what happened), is the worst thing you could possibly do short of theft.