Lubrifiquei a corrente.

Lubrifiquei is the 1st person singular form of lubrificar in the pretérito perfeito simples.

In practical terms, it means:

• I lubricated
• I oiled / I greased (depending on context)
• a completed action in the past

So the sentence describes something the speaker finished doing.

This is a spelling change that keeps the pronunciation consistent.

The verb is lubrificar. In forms where c would come before e or i, Portuguese often changes c to qu to preserve the hard k sound.

So:

• lubrificar → lubrifiquei
• not lubrificei, because that would suggest a softer sound

The same thing happens in other verbs:

• ficar → fiquei
• explicar → expliquei

So qu here is mainly an orthographic change to keep the sound right.

Because Portuguese often omits the subject pronoun when the verb form already makes the subject clear.

Lubrifiquei already tells you the subject is I, so eu is not necessary.

You could say:

• Eu lubrifiquei a corrente.

But that usually adds emphasis, contrast, or clarity, for example:

• Eu lubrifiquei a corrente, não o Pedro.
  I lubricated the chain, not Pedro.

In neutral sentences, leaving out eu is very normal in European Portuguese.

Because a is the feminine singular definite article, meaning the.

So:

• a corrente = the chain

You use a because corrente is a feminine noun, and because the sentence refers to a specific chain rather than chains in general.

Yes, corrente is a feminine noun.

That is why you get:

• a corrente
• uma corrente
• a corrente nova

If you use adjectives or pronouns with it, they also need to agree in the feminine form.

Here, corrente means chain.

That said, corrente can mean other things in other contexts, such as:

• current (for example, electrical current)
• stream
• trend or movement

But in Lubrifiquei a corrente, the natural reading is the chain, because that is something you lubricate.

A rough European Portuguese pronunciation is:

lubrifiquei a corrente
[lubɾifiˈkej ɐ kuˈʁẽt(ɨ)]

A few useful points:

• lubrifiquei is stressed on the last syllable: lu-bri-fi-QUEI
• the a article is usually a reduced sound, roughly uh
• rr in corrente is a strong Portuguese r
• the final e in corrente is often very weak in Portugal

If you are aiming for European Portuguese, vowel reduction is one of the big features to notice.

In most everyday contexts, the best English translation is I lubricated the chain.

Portuguese pretérito perfeito simples usually refers to a finished past action.

Although English sometimes uses have lubricated, Portuguese does not match English tenses one-to-one. In European Portuguese, tenho lubrificado usually suggests something more like a repeated or ongoing action over a period of time, not just one completed action.

So for a single finished event, lubrifiquei is the normal choice.

Yes. Lubrifiquei a corrente is correct and natural, especially in a technical, mechanical, or maintenance context.

In more everyday speech, people might also say things like:

• Pus óleo na corrente.
• Oleei a corrente.

But lubrifiquei a corrente is absolutely fine and sounds clear and standard.

In standard European Portuguese, you would typically say:

Lubrifiquei-a.

Why?

• corrente is feminine singular
• so the direct object pronoun is a
• in this kind of affirmative sentence, the pronoun usually comes after the verb in European Portuguese
• it is linked with a hyphen: lubrifiquei-a

So:

• Lubrifiquei a corrente.
• Lubrifiquei-a.

This is a useful pattern to learn, even though in casual speech people sometimes repeat the noun instead.