Nie trzeba było tankować rano, bo było jeszcze paliwo.

Trzeba is an impersonal word meaning it is necessary / one must / there is a need to.
In the past, Polish often says trzeba było + infinitive to mean it was necessary to... or, with nie, it wasn’t necessary to...

So:

• Trzeba było tankować = It was necessary to refuel
• Nie trzeba było tankować = It wasn’t necessary to refuel

This construction does not say who exactly didn’t need to do it. The person is understood from context, or it stays general.

By contrast:

• Nie musiałem tankować = I didn’t have to refuel
• Nie musieliśmy tankować = We didn’t have to refuel

Those forms clearly name the subject.

Here było puts the idea of necessity into the past.

• Trzeba tankować = It is necessary to refuel
• Trzeba było tankować = It was necessary to refuel
• Nie trzeba było tankować = It was not necessary to refuel

So było is not the main meaning by itself here; it helps express past time with the impersonal expression trzeba.

After trzeba and trzeba było, Polish normally uses the infinitive.

Examples:

• Trzeba iść = One must go
• Trzeba było czekać = It was necessary to wait
• Nie trzeba było tankować = It wasn’t necessary to refuel

So tankować stays in the infinitive because it depends on trzeba było.

Because the two było forms are doing two different jobs:

1. Nie trzeba było tankować rano
   Here było is part of the past expression trzeba było = it was necessary

2. bo było jeszcze paliwo
   Here było simply means there was / there still was

So even though the word is the same, the function is different in each part.

Bo means because.

It is very common in everyday spoken and written Polish. It sounds natural and conversational.

You could also use:

• ponieważ = because / since
• gdyż = because, more formal or bookish

So:

• Nie trzeba było tankować rano, bo było jeszcze paliwo.
  very natural, everyday Polish

• Nie trzeba było tankować rano, ponieważ było jeszcze paliwo.
  also correct, a bit more formal

Rano is an adverb meaning in the morning / this morning / in the morning time, depending on context.

Polish often uses simple adverbs of time without a preposition:

• rano = in the morning
• wieczorem = in the evening
• nocą = at night
• dzisiaj = today

So:

• tankować rano = to refuel in the morning

You would not say w rano here.

Here jeszcze means still.

So było jeszcze paliwo means there was still fuel or there was fuel left.

It adds the idea that the fuel had not run out yet.

Compare:

• Było paliwo = There was fuel
• Było jeszcze paliwo = There was still fuel / there was fuel left

That small word gives the second clause a more natural reason for the first one.

Paliwo is in the nominative singular here.

In the clause było jeszcze paliwo, the meaning is existential: there was still fuel.
Polish often uses the nominative in this kind of statement.

Also, paliwo is a neuter noun, so the past tense form is było to match that neuter singular idea.

Because paliwo is a neuter singular noun.

Past tense to be agrees in gender and number:

• był = masculine singular
• była = feminine singular
• było = neuter singular
• byli / były = plural

Since paliwo is neuter singular, the correct form is było.

Both are possible, but they give slightly different shades of meaning.

• tankować is imperfective
• zatankować is perfective

In this sentence, tankować sounds natural because the statement is about whether refueling was necessary at all.

• Nie trzeba było tankować rano = It wasn’t necessary to refuel in the morning

If you say:

• Nie trzeba było zatankować rano

it may sound less natural to many learners at first, though it can appear in some contexts. In everyday usage, trzeba było + imperfective infinitive is very common when talking about general necessity.

So for a learner, tankować is the safer and more natural choice here.

The subject is left unspecified.

That is normal with trzeba było. Polish often uses this structure when the doer is obvious from context or not important.

Depending on the situation, it could mean:

• I didn’t need to refuel
• we didn’t need to refuel
• you didn’t need to refuel
• it wasn’t necessary to refuel

The sentence itself does not force one specific subject. Context decides.

Yes. Polish word order is fairly flexible, although the original version sounds very natural.

Original:

• Nie trzeba było tankować rano, bo było jeszcze paliwo.

Possible variations:

• Bo było jeszcze paliwo, nie trzeba było tankować rano.
• Nie trzeba było rano tankować, bo było jeszcze paliwo.
• Rano nie trzeba było tankować, bo było jeszcze paliwo.

These all keep basically the same meaning, but the emphasis changes:

• putting rano earlier highlights the time
• putting the bo clause first highlights the reason

The original order is probably the most neutral.

Because Polish has no articles like a, an, or the.

So paliwo can mean:

• fuel
• the fuel
• some fuel

The exact meaning depends on context.

In było jeszcze paliwo, English naturally translates it as there was still fuel or there was still some fuel left, even though Polish does not explicitly mark that with an article.