Expired cache files are not cleared

Hi,

I have a problem, expired cache files are not cleared.

Saving cache like (this for example) version CI 4.1.1

PHP Code:

if (! $foo = cache('foo'))
{
    echo 'Saving to the cache!<br />';
    $foo = 'foobarbaz!';

    // Save into the cache for 5 minutes
    cache()->save('foo', $foo, 300);
}

echo $foo; 


Files are supposed to delete themselves, right?

Or do I have to do something manually to delete them?

Thank you

Ángel