I would see it a bit differently than @Tim does, and say that we know that cars are devices largely made up of synthetic materials and components that do not exist in nature but which are fabricated by human beings, and they do not self assemble but only come into existence thru human manufacture. So it is unreasonable to expect they could come into existence thru natural processes.
The same does not apply to the bacterial flagellum. Obviously.
Yeh, that’s probably a better articulation of what I was groping towards. 
so let me ask you that: do you agree that according to the evidence we have there are no small steps between two biological complex systems?
so? maybe there is an unknown natural process which can produce a car? can you refute that possibility?
No.
No.
However, there is a known natural process that produces bacterial flagella. So I really don’t see where you are going with this.
if so you dont know if a car needs design.
Which, even if we accepted that, proves what exactly?
Are you serious? Or perhaps you simply do not recognize that a natural process works on nature or natural things and a car is not part of nature.
I must admit that @scd’s absurd hypotheticals are getting so far from reality that I’m having increasing trouble keeping track of ‘getting from here to there’. What’s next? A starship whose larval stage is a highway-tunnel-borer? 
Only if we pretend the absurd hypotheticals you come up are reasonable possibilities. But, otherwise, I do know that every car that is known to exist was designed…
I must say, your reasoning, such as it is, is very difficult to follow. To paraphase: “There could be some unknown natural processes that end up with a Buick Regal, so Buick Regals don’t need to be designed. However, at least some Buick Regals are designed, so we know that all bacterial flagella are designed.”
Can you help me to see the logic in that?
You are still confused. Whether the Big Bang was by design or not it was a natural process and this is what all mainstream scientists say whether they are theists or not.
From motors to PC fans, I tire at your faulty analogies and your seemingly hopeless confusion.
Fans have a primary purpose, which is to get rid of stale, warm air. They can be fitted into devices like car engines or computers. If I get the fan working, it can function as my cloth dryer, or help to cool me. Thus, the fan can be functional until it gets installed into the PC.
I found this Quora thread on things you can do with a PC fan. Although the thread is about what can be done with spare PC fans, everything still applies to PC fans meant for integration into a PC.
Why not the converse?
I did briefly consider starting a thread “Do self-replicating bad analogies exist?” They do seem to be spreading.
Even those don’t exist 
and what seems to be spreading is conscious, unintelligent bad analogies.
I was trying to keep my life-cycle reasonably analogous to that of many insects – where the larva burrows into, and feeds on, dead or living flora or fauna, before emerging to fly away as an adult. It was also somewhat of a mashup of Elon Musk’s Boring Company and the Vorlon living starships from Babylon 5. 
But if this is insufficiently absurd a hypothetical for you, then have at it it. The absurdity is only limited by your imagination. 
im not confuse at all. this depend on the definition of “natural”. if we consider anything that isnt made by design as “natural”, then a guided big bang was not natural. so this depend on the definition.
no. im talking about internal function in thhe PC. not a function that is possible with external designer like humans. this is a big difference. so do you think that we can add to a PC a fan bt small functional steps, or we need at least few parts to make it functional to the PC?
You are aware that PC fans have evolved considerably in the last few decades? Both in materials used (stiffer, to allow closer tolerances, and thus greater efficiency) and in design? These improvements have generally been by “small functional steps”. 
we are talking about a minimal fan, not how we can change an existing fan to another one. and a minimal fan need at least few parts for its minimal function.
No scd, “we” were doing nothing of the sort. You are merely unilaterally moving the goalposts yet again.
And by arbitrarily excluding external functionality and internal evolution, you have defined away any relevance the PC fan might have as an analogy to biological evolution.
So now you need to move on to try, unsuccessfully, your next bad analogy.
Again, this line of discussion seems to me to be entirely irrelevant.
Much of the evidence for evolution lies in the fact that transitional forms exist in the fossil record, and also that all forms extant and extinct can be easily fitted into a nested hierarchy. Neither of these are necessarily the case for designed entities.
So even if it is not possible for transitional forms to exist for designed objects like PC fans, that does not address the evidence for evolution in the least. As a matter of fact, it only strengthens that evidence.
TBH, I don’t think the confusion here is necessarily on your part, nor even that of @scd. Instead, I believe the confusion reflects an incoherence at the heart of the “theistic evolution/evolutionary creationism” paradigm. Under this paradigm the universe is somehow guided by a deity to produce specific outcomes (eg bipedal primates with big brains capable of moral reasoning) thru processes that are indistinguishable from those that are stochastic and unguided. Even so, the guiding hand of this deity is somehow to be discerned in these processes. It seems to me far more parsimonious to posit that those processes appear so convincingly to be unguided because they are unguided.