Ο κινητήρας λειτουργεί καλά.

Ο is the masculine singular definite article, so it means the.

In Ο κινητήρας λειτουργεί καλά, it goes with κινητήρας and shows that the noun is definite: the engine.

A few useful article forms to compare:

• ο = the for masculine singular nouns
• η = the for feminine singular nouns
• το = the for neuter singular nouns

So ο κινητήρας = the engine.

Κινητήρας is a masculine singular noun, and -ας is a very common ending for masculine nouns in Greek.

In this sentence, κινητήρας is the subject, so it appears in the nominative singular form:

• ο κινητήρας = the engine

If you keep studying Greek, you will see that nouns change form depending on their role in the sentence. For example, masculine nouns in -ας often have different endings in other cases.

It is pronounced roughly like:

kee-nee-TEE-ras

The stress is on τή.

Breaking it up:

• κι = kee
• νη = nee
• τή = TEE
• ρας = ras

A more precise pronunciation is approximately /ciniˈtiras/ in Modern Greek.

Λειτουργεί comes from the verb λειτουργώ, which means things like:

• to function
• to operate
• to work

So in this sentence, λειτουργεί means works / functions / operates.

With a machine like an engine, English might naturally say:

• The engine works well
• The engine is functioning well
• The engine runs well

All of those fit the Greek sentence pretty well, depending on context.

Because it is the 3rd person singular present tense form of λειτουργώ.

That means it matches a subject like:

• he
• she
• it
• or a singular noun such as ο κινητήρας

So:

• λειτουργώ = I function / I work
• λειτουργείς = you function / you work
• λειτουργεί = he/she/it functions / works

Since ο κινητήρας is singular, Greek uses λειτουργεί.

Because Greek often does not need subject pronouns when the verb ending already tells you who or what the subject is.

In English, you must say:

• It works well

In Greek, the verb ending often gives enough information, so Greek commonly says simply:

• Λειτουργεί καλά = It works well / It functions well

In your full sentence, the subject is stated explicitly:

• Ο κινητήρας λειτουργεί καλά

So there is no need for a separate word meaning it.

Καλά is an adverb, and here it means well.

It describes how the engine functions:

• λειτουργεί καλά = works well

This is important because learners often compare it with καλός / καλή / καλό, which are adjectives meaning good.

Compare:

• καλός κινητήρας = a good engine
  (καλός describes the noun)
• Ο κινητήρας λειτουργεί καλά = The engine works well
  (καλά describes the verb)

So καλά is used because you are modifying λειτουργεί, not κινητήρας.

Because the sentence needs an adverb, not an adjective.

• Adjective = describes a noun
• Adverb = describes a verb

Here, the noun is κινητήρας and the verb is λειτουργεί.

You are not saying:

• The engine is good

You are saying:

• The engine works well

So Greek uses καλά.

A useful comparison:

• Ο κινητήρας είναι καλός. = The engine is good.
• Ο κινητήρας λειτουργεί καλά. = The engine works well.

Greek word order is more flexible than English, but this sentence uses the most neutral, natural order:

• Ο κινητήρας λειτουργεί καλά.

That is the standard way to say it.

You may sometimes see different orders for emphasis, but not all of them sound equally natural in every context. For a learner, the safest version is the original one.

For example:

• Ο κινητήρας λειτουργεί καλά. = neutral
• Καλά λειτουργεί ο κινητήρας. = possible, but gives more emphasis to well
• Λειτουργεί καλά ο κινητήρας. = also possible in context

So yes, Greek allows movement, but the original order is the best default choice.

Yes, stress matters a lot in Greek. You should pay attention to the accent marks.

In this sentence:

• Ο → no written accent
• κινητήρας → stress on τή
• λειτουργεί → stress on the final εί
• καλά → stress on the final λά

So the sentence sounds roughly like:

o kee-nee-TEE-ras lee-tour-GHEE ka-LA

If you put the stress in the wrong place, Greek may sound unnatural, and sometimes it can even create confusion.

Λειτουργεί is completely correct and natural, especially when talking about whether a machine or system is functioning properly.

However, in everyday speech, Greek may also use δουλεύει:

• Ο κινητήρας δουλεύει καλά.

That also means The engine works well.

A rough difference:

• λειτουργεί = a bit more neutral, technical, or formal
• δουλεύει = very common in everyday speech

Both are useful to know.

You add δεν before the verb:

• Ο κινητήρας δεν λειτουργεί καλά.

That means:

• The engine doesn’t work well
• or The engine is not functioning well

So the pattern is:

• λειτουργεί = works / functions
• δεν λειτουργεί = doesn’t work / isn’t functioning

Yes. Greek λειτουργεί καλά is broad and can fit several natural English translations depending on context:

• works well
• functions well
• operates well
• sometimes runs well for machines like engines

The exact English choice depends on what sounds most natural in the situation, but the Greek itself is straightforward and idiomatic.

It is neutral.

It sounds perfectly normal in standard Greek and would fit:

• everyday conversation
• written explanations
• technical discussion
• general statements

It is not especially formal, but it is a little more precise than a very colloquial version with δουλεύει.

So it is a very good sentence for learners to know.