Mechanik mówi, że silnik działa dobrze.

Mechanik is in the nominative case because it is the subject of the sentence — the person doing the action of speaking.

• mechanik = the mechanic
• In this sentence, the mechanic is the one who mówi (says / is saying)

So the basic structure is:

• Mechanik = subject
• mówi = verb
• że silnik działa dobrze = what he says

Mówi can mean says, is saying, or speaks, depending on context.

In this sentence, Mechanik mówi, że... is most naturally:

• The mechanic says that...

Why? Because it introduces reported speech: someone is stating something.

Compare:

• Mechanik mówi po polsku. = The mechanic speaks Polish.
• Mechanik mówi, że silnik działa dobrze. = The mechanic says that the engine is working well.

So here, mówi is best understood as says.

In Polish, a comma is normally used before że when it introduces a subordinate clause.

So:

• Mechanik mówi, że silnik działa dobrze.

This is standard punctuation.

The part after że is a clause meaning something like that the engine works well.

This is one of the most useful comma rules in Polish:

• comma before że
• also often before words like bo, który, gdy, etc., depending on structure

Że usually means that.

In this sentence:

• Mechanik mówi, że silnik działa dobrze.
• The mechanic says that the engine works well.

It introduces the content of what someone says, thinks, knows, etc.

Very common patterns:

• Mówię, że... = I say that...
• Myślę, że... = I think that...
• Wiem, że... = I know that...

So że is a very common connector in Polish.

Because silnik is the subject of the second clause:

• że silnik działa dobrze
• that the engine works well

Here, the engine is the thing doing the action of działa (works / runs / functions), so it stays in the nominative:

• silnik = engine

You would see silnika in other roles, for example:

• Nie ma silnika. = There is no engine. / It doesn’t have an engine.
• Słucham silnika. = I’m listening to the engine.

But here, it is simply the subject, so silnik is correct.

Działa literally means works, is working, or functions.

In the case of a machine or engine, English may translate it in a few natural ways:

• The engine works well
• The engine is working well
• The engine runs well

All of these are possible depending on context.

Polish działać is quite broad and is often used for:

• machines
• devices
• systems
• software
• engines

Examples:

• Telefon działa. = The phone works.
• To nie działa. = This doesn’t work.
• Silnik działa dobrze. = The engine is working well / runs well.

Sometimes yes, but działa is the more neutral and common choice for functions/works properly.

Compare the feel:

• silnik działa dobrze = the engine works/functions well
• silnik pracuje dobrze = the engine is running well / operating well

With engines, pracować can also be used, especially in technical or mechanical contexts, but działać is very common and natural.

So a learner should understand:

• działać = to function, work
• pracować = to work, operate, be running

In this sentence, działa dobrze sounds very normal.

Because dobrze is an adverb, while dobry is an adjective.

Here, dobrze describes how the engine works:

• działa dobrze = works well

You need an adverb because it modifies the verb działa.

Compare:

• dobry silnik = a good engine
  
  • here dobry describes the noun silnik
• silnik działa dobrze = the engine works well
  
  • here dobrze describes the verb działa

This is similar to English:

• good engine
• works well

Yes, Polish word order is more flexible than English, although the original sentence is the most neutral.

Standard neutral order:

• Mechanik mówi, że silnik działa dobrze.

Possible alternatives:

• Że silnik działa dobrze, mówi mechanik.
• Mechanik mówi, że dobrze działa silnik.
• Silnik działa dobrze, mówi mechanik.

But these alternatives change the emphasis or sound more literary, marked, or context-dependent.

For a learner, the safest default is:

• subject + verb + że-clause

So the original sentence is the best basic model.

No. In Polish, subject pronouns are often omitted because the verb form already shows the person.

• mówi = he/she/it says
• Since mechanik is already present, there is no need to add on

So:

• Mechanik mówi... = perfectly natural
• On mówi... = He says...
• Mechanik on mówi... = usually unnecessary or awkward unless very emphatic

Polish often leaves out pronouns where English would use them.

A simple English-friendly guide:

• że sounds roughly like zhe
  • the ż is like the s in measure or the g in genre
• działa sounds roughly like JWAH-wa or DZHWA-wa, depending on how carefully you analyze the first sound cluster

A slightly more detailed breakdown:

• dz = a sound like ds or dz
• ia after ł-type surroundings can create a glide
• ł sounds like English w
• so działa is approximately DYAH-wa / JWAH-wa to an English ear

Also:

• mówi ≈ MOO-vee
• silnik ≈ SEEL-neek
• mechanik ≈ meh-HA-neek

The stress in Polish is usually on the second-to-last syllable:

• mechanik
• mówi
• silnik
• działa
• dobrze

Yes, mówić is imperfective.

That matters because it often suggests:

• a general statement
• an ongoing act of speaking
• habitual or repeated speech
• neutral present-tense reporting

So Mechanik mówi, że... means something like:

• The mechanic says that...
• The mechanic is saying that...

If you wanted a completed one-time action in the past, you would often use the perfective verb powiedzieć:

• Mechanik powiedział, że silnik działa dobrze.
• The mechanic said that the engine works / was working well.

For this sentence, mówi is completely natural in the present.

Usually no, not in normal standard Polish.

In English, you can say:

• The mechanic says the engine works well.

But in Polish, you normally need że:

• Mechanik mówi, że silnik działa dobrze.

Without że, the sentence would usually sound wrong or unnatural in standard Polish.

So unlike English, Polish generally keeps the equivalent of that in this structure.

It is reported speech.

• Mechanik mówi, że silnik działa dobrze.
• The mechanic says that the engine works well.

It reports the content of what the mechanic says, rather than quoting his exact words.

A direct quote would look like this:

• Mechanik mówi: Silnik działa dobrze.
• The mechanic says: The engine works well.

So:

• with że = reported speech
• with a colon or quotation marks = direct speech

A very useful pattern is:

• [person] mówi, że [clause]
• [person] says that [clause]

Examples:

• Anna mówi, że jest zmęczona. = Anna says that she is tired.
• Nauczyciel mówi, że to ważne. = The teacher says that this is important.
• Mechanik mówi, że silnik działa dobrze. = The mechanic says that the engine works well.

This is a high-frequency Polish sentence pattern, so it is worth memorizing as a whole structure.