Count custom posts type and filter by tag

wp_count_posts is not affect your custom query. You can use found_posts to return the number of posts from the custom query. So try to change the code after your loop query as follows. Hope it helps.

if ($loop->have_posts()) :
    $count_posts = $loop->found_posts;
    echo "<p>Total:  $count_posts cars</p>";
else :
    echo "<p>No cars available.</p>";
endif;
wp_reset_query();