Водитель проверил двигатель.

Двигатель is the direct object, so it is in the accusative case.

However, for many masculine inanimate nouns, the accusative singular looks exactly the same as the nominative singular. So:

• nominative: двигатель
• accusative: двигатель

That is why you do not see a new ending here.

That is a very common question. In this sentence, you mostly know from:

1. Normal word order: Russian often uses subject + verb + object as the neutral order.
2. Meaning/context: a driver checking an engine is more natural than an engine checking a driver.

So Водитель проверил двигатель is understood as The driver checked the engine.

This is one of those cases where Russian relies on more than just endings.

Проверил is the perfective past tense form of проверить. It presents the action as completed: the checking was done.

• проверил = checked, finished checking
• проверял = was checking / checked repeatedly / used to check

So this sentence describes one completed check.

It is the masculine singular past tense form of проверить.

Russian past tense is built from the verb stem plus forms based on -л:

• masculine: проверил
• feminine: проверила
• neuter: проверило
• plural: проверили

Because водитель is masculine singular, the verb is проверил.

In Russian, a final ь does not automatically mean a noun is feminine.

Both водитель and двигатель belong to a common masculine noun pattern ending in -тель. So they are masculine even though they end in a soft sign.

Other masculine nouns of this type include:

• учитель
• писатель
• строитель

So -ь here is just part of the noun’s ending pattern.

The stress is:

• води́тель
• прове́рил
• дви́гатель

So the full sentence is:

Води́тель прове́рил дви́гатель.

Stress matters in Russian, so it is good to learn words together with their stress.

Russian has no articles. There is no direct equivalent of the or a/an in ordinary sentences.

So Водитель проверил двигатель can mean:

• The driver checked the engine
• A driver checked an engine

Which one sounds best depends on context. English must choose; Russian usually does not.

Yes. Russian word order is more flexible than English, but changing it often changes the emphasis.

Neutral order:

• Водитель проверил двигатель.

Possible alternative:

• Двигатель водитель проверил.
  This puts extra focus on engine.

Another:

• Водитель двигатель проверил.
  This can emphasize that it was the engine that was checked.

So the basic meaning can stay similar, but the information focus changes.

The dictionary forms are:

• водитель — noun
• проверить — verb, perfective
• двигатель — noun

It is also useful to know the imperfective partner of the verb:

• проверять — imperfective
• проверить — perfective

Russian verbs are often learned in these aspect pairs.