Eu preciso tirar o casaco porque está muito quente.

Yes. Tirar has a broad meaning: to remove, take out, take away, take off.

With clothes, tirar is the normal verb for taking something off:

• tirar o casaco = take off the coat/jacket
• tirar a camisa = take off the shirt
• tirar os sapatos = take off the shoes

So in this sentence, tirar o casaco is exactly the natural way to say take off the coat.

In Brazilian Portuguese, the usual pattern is precisar + infinitive when another verb follows:

• Preciso sair = I need to leave
• Preciso estudar = I need to study
• Preciso tirar o casaco = I need to take off my coat

When precisar is followed by a noun, de is very common:

• Preciso de ajuda = I need help
• Preciso de dinheiro = I need money

So here, because tirar is a verb, preciso tirar is the expected structure.

Yes. Very often, you can simply say:

• Preciso tirar o casaco porque está muito quente.

That sounds completely natural.

Portuguese often drops subject pronouns when the verb form already makes the subject clear. Preciso clearly means I need, so eu is optional.

You might keep eu for:

• emphasis
• contrast
• clarity

For example:

• Eu preciso tirar o casaco, mas ele não. = I need to take off my coat, but he doesn’t.

Because in Portuguese, when the possession is obvious, people often use the definite article instead of a possessive.

So:

• tirar o casaco
• tirar meu casaco

can both mean take off my coat, depending on context.

Using o casaco sounds very natural if everyone already knows it is your coat. Portuguese does this a lot with clothing, body parts, and personal items.

Examples:

• Lavei as mãos. = I washed my hands
• Vou calçar os sapatos. = I’m going to put on my shoes

Using meu is still possible, but it adds a little more emphasis to ownership.

Here, está muito quente means it is very hot.

Portuguese often does not need an explicit subject where English uses it. The idea is understood from context: the room, the weather, the environment, the situation, and so on.

So:

• Está muito quente. = It’s very hot.

There is no need to say a word for it.

This is very common with weather and general conditions:

• Está frio. = It’s cold.
• Está escuro. = It’s dark.
• Está barulhento aqui. = It’s noisy here.

Because estou muito quente usually does not mean I feel hot in the normal everyday sense.

If you want to say I’m hot because of the temperature, the natural expression is:

• Estou com calor.

So a Brazilian would usually say:

• Preciso tirar o casaco porque estou com calor.
• Preciso tirar o casaco porque está muito quente.

These are both natural, but they mean slightly different things:

• está muito quente = the environment is very hot
• estou com calor = I personally feel hot

Also, estou quente can sound odd, and in some contexts it can sound sensual or sexual, so learners are usually told to avoid it for this meaning.

It can mean either hot or warm, depending on context.

Examples:

• café quente = hot coffee
• água morna = lukewarm water
• roupa quente = warm clothing

In this sentence, because of muito and the idea of taking off a coat, quente is best understood as very hot.

One important note: quente is about temperature, not spiciness. For spicy food, Portuguese usually uses words like:

• picante
• apimentado

So comida quente means hot food in temperature, not spicy food.

Because here muito is an adverb, and adverbs do not change for gender or number.

It modifies the adjective quente:

• muito quente = very hot

When muito means very, it stays muito:

• muito frio = very cold
• muito bonita = very beautiful
• muito rápido = very fast

But when muito is an adjective meaning much/many/a lot of, it does change:

• muito dinheiro = a lot of money
• muita água = a lot of water
• muitos livros = many books
• muitas pessoas = many people

So in your sentence, muito means very, not much, so it stays muito.

Here, porque means because:

• ...porque está muito quente. = ...because it’s very hot.

Portuguese has four similar forms, which often confuse learners:

• porque = because
• por que = why / for what reason
• por quê = why, but usually at the end of a clause
• porquê = the reason

Examples:

• Por que você saiu? = Why did you leave?
• Você saiu por quê? = You left why?
• Saí porque estava cansado. = I left because I was tired.
• Não entendi o porquê. = I didn’t understand the reason.

In your sentence, the cause is being introduced, so porque is the correct form.

It can mean either, depending on context.

In Brazilian Portuguese, casaco is a general word for an outer layer of clothing worn because of cold weather. In English, that could be:

• coat
• jacket
• cardigan
• outer layer

If you want to be more specific, other words may be used:

• jaqueta = jacket
• blusa de frio = sweatshirt / warm top / light jacket, depending on context
• sobretudo = overcoat

So casaco is a good general word, and in your sentence coat is a perfectly good translation.

Yes. In everyday Brazilian speech, people often shorten está to tá:

• Eu preciso tirar o casaco porque tá muito quente.
• Preciso tirar o casaco porque tá muito quente.

That sounds very natural in conversation.

Another very common way to express the idea would be:

• Tô com calor, preciso tirar o casaco.

Here:

• tô = spoken short form of estou
• com calor = feeling hot

Your original sentence is fully correct and natural, especially in standard speech or writing.

A rough Brazilian Portuguese pronunciation would be:

eu preh-SEE-zoo chee-RAHR oo kah-ZAH-koo por-KEH es-TAH MOO-ee-too KEN-chee

A few useful notes:

• preciso has stress on si: preh-SEE-zoo
• tirar often sounds like chee-RAHR in many Brazilian accents, though some speakers are closer to tee-RAHR
• porque has stress on the last syllable: por-KEH
• está has stress on the last syllable: es-TAH
• quente often sounds like KEN-chee in many Brazilian accents
• in casual speech, está often becomes tá

So in very natural everyday speech, you may hear something close to:

Preciso tirar o casaco porque tá muito quente.