Sorry we're talking about a hypothetical car engine, and as an analogy to software development. I'm not an expert in designing car engines like you, but acting like this example being not fully realistic is some kind of "gotcha" for the point I'm making is really frustrating.

The point that I am making (obviously, I think) is that tradeoffs exist, even if you don't think the right decision was made, your full view into the trade space is likely incomplete, or prioritizes something different than the engineers.

Based on the replies, saying there's a hypothetical 2mpg improvement to be had was a mistake, everyone is latching on to that like there's some actual engine we're investigating.

You made a "well actually" comment in which you demonstrated your lack of knowledge on the topic, _and_ stated a truism which didn't apply to the thing you were replying to.

Yes, I'm sure most people on this website have ran into seemingly bad design choices which made sense once they knew more context. But that doesn't mean that all bad design choices are like this.

Specifically dumb oil filter placement is an example of such a case where the _only_ legitimate justification is design cost saving for the manufacturer (re-using an existing design meant for a different car).

You can maybe argue that saving on design costs (and I guess also re-tooling costs) is a saving that gets passed onto the consumer. But that consumer is unlikely to feel like they're saving much money when cars depreciate faster than ice cubes in the desert, and when their oil change is 2+ times more expensive every 6 months. Really that cost savings will only really benefit the manufacturer (well, at least until they tarnish their reputation).

No, the point is that the GP statement missed the point. Say we hear about a company laying off 10% of workers, and someone says "What if they needed to lay off those workers in order to meet their HIPAA obligations and protect user privacy?" Now clearly that would be an argument that is either bad faith, or just spectacularly uninformed. We do not then go on to discuss the relative importance of HIPAA compliance versus employment. The reason companies lay off workers is because of a decline in market demand or efforts at cost cutting. That is the reason. It's not to help the environment. It's not to protect customer data. It's not because this is the year of the Pig. Anyone who makes those arguments should get responded to in a way to clearly points out it is a specious argument.

The reason why automakers place serviceable parts in bad locations is due to either incompetence (If you are, say, Bentley) or malicious design (almost everyone else) -- e.g. they do not prioritize serviceability. Car makers really hate that ordinary people can repair their own vehicles. There were proposals in the 1960s to try to lock shut the hood so that car owners wouldn't be able to open it and service the cars on their own. Hyundai just announced that they will not allow car owners to retract their own parking brakes when they want to replace brake pads. You need a login with a website and prove that you are a professional mechanic before you can retract your own parking brakes. This is done, ostensibly, for "cyber security" reasons. But the real reason is that Hyundai does not want people to be able to service their own cars, they want you to take the car to a dealer. They also are not fans of independent mechanics, they would prefer if everyone that touched the car had a business relationship with Hyundai and was under contract with them. The fact that you can work on your car is an endless source of pain for manufacturers, and when they repeatedly make it hard to work on your car, or try to lock down parts so that you can't pull an old seat heater from the junkyard and use it to replace your own failed seat heater -- that is all part of the war on independent repair.

So what should be discussed is the environment of hostility to serviceability, everything from insisting that transmission oil is "lifetime" to forcing you to pay money to the manufacturer if you want to read the data from your sensors, or making it extremely hard to do simple things like changing a headlight or replacing a battery. All of that is part of the same issue, which is hostility to end user repair. It has nothing to do with improving gas mileage, or ending world hunger, or celebrating the Year of the Pig. These are all equally specious arguments.