Thợ máy thay dầu.

• thợ = worker, craftsperson, tradesperson
• máy = machine
• thợ máy = mechanic
• thay = change, replace
• dầu = oil

So the sentence is literally something like mechanic change oil.

Because Vietnamese spelling usually separates syllables with spaces, even when those syllables form one lexical word or fixed expression.

So thợ máy is best learned as one compound noun meaning mechanic, not as two separate English-style words in the sentence.

This is very common in Vietnamese:

• xe máy = motorbike
• bệnh viện = hospital
• học sinh = student

It follows the basic Vietnamese pattern:

• Subject: thợ máy
• Verb: thay
• Object: dầu

So it is:

Thợ máy + thay + dầu
= The mechanic changes oil / changes the oil

In this sentence, the word order is basically the same as English: subject + verb + object.

Vietnamese does not use articles the way English does.

So thợ máy can mean:

• a mechanic
• the mechanic
• mechanics in a general sense

And dầu can mean:

• oil
• the oil

You understand which one is meant from context.

That means Thợ máy thay dầu could be interpreted as:

• A mechanic changes oil
• The mechanic changes the oil
• Mechanics change oil

You usually do not know from the noun alone. Vietnamese nouns are often neutral about number unless something in the sentence makes it clear.

If you want to make it explicit, you can add words like:

• một thợ máy = one mechanic, a mechanic
• các thợ máy = mechanics
• những thợ máy = mechanics, some mechanics

So in the original sentence, thợ máy is number-neutral.

It can mean both, and in everyday usage it is the normal way to say change the oil.

In maintenance contexts, thay dầu is a very common collocation. It usually means replacing old oil with new oil, such as engine oil.

So an English speaker can safely understand it as:

• change the oil
• do an oil change

No. After a transitive verb like thay, the object can come directly after it.

So:

• thay dầu = change oil

You do not need a preposition like for or the here.

And you do not need a classifier in this sentence either. Classifiers are usually used when you are counting or specifying nouns, especially concrete countable things. Dầu is a mass noun, so a classifier is not expected here.

Vietnamese verbs do not change form for tense the way English verbs do.

The bare sentence Thợ máy thay dầu is tense-neutral. Depending on context, it could mean:

• The mechanic changes oil
• The mechanic is changing the oil
• The mechanic changed the oil

If you want to make time clearer, Vietnamese often adds time words or aspect markers:

• Thợ máy đang thay dầu. = The mechanic is changing the oil.
• Thợ máy đã thay dầu. = The mechanic changed / has changed the oil.
• Thợ máy sẽ thay dầu. = The mechanic will change the oil.

A rough guide:

• thợ: sounds somewhat like t-huh with a short, clipped, low tone
• máy: roughly like my with a rising tone
• thay: roughly like tie or thai, level tone
• dầu: roughly like zow in northern Vietnamese, with a falling tone

A few useful notes:

• th in Vietnamese is an aspirated t, not like English th
• d in northern Vietnamese sounds like English z
• tones matter, so copying the pitch pattern is important

If you are learning pronunciation, it is best to hear a native speaker say the whole phrase rather than rely only on English approximations.

It often means mechanic in a general sense, especially someone who works with machines or engines. In context, it can certainly refer to an auto mechanic.

Because the sentence mentions thay dầu, many learners will naturally understand it as an automotive or engine-maintenance context.

If you want to be more specific, Vietnamese can say things like:

• thợ sửa xe = vehicle mechanic / repairer
• thợ sửa ô tô = car mechanic
• thợ sửa xe máy = motorbike mechanic

But thợ máy by itself is perfectly natural.

Yes, you could, but it is usually not necessary.

• thợ máy already means mechanic
• người thợ máy is more like the mechanic / the mechanic person / the worker who is a mechanic

Adding người can sound a bit more explicit or descriptive, but in a simple sentence like this, Thợ máy thay dầu is more direct and natural.

It can be either, depending on context.

Without extra markers, Vietnamese bare sentences are flexible. So Thợ máy thay dầu may mean:

• a general statement: Mechanics change oil
• a description of a current or specific situation: The mechanic changes/is changing the oil
• a caption or note: Mechanic changing oil

Context tells you which reading is intended. This flexibility is very normal in Vietnamese.