That search (e.g. `ford fiesta water pump`) is consistent for me as well, except for an "explore more" section in the middle of the results.

So it does seem to be specific searches where it gives up after the first 7-10 results (or decides to show you some more related results after 20-30 additional unrelated results).

I wonder if this is algorithmic. E.g. people searching for a specific "how to replace/fix ..." are not going to click on results from their recommended feed, so the algorithm could have learned to keep those results fixed. However, someone looking for a piece of entertainment (trailer, book review, etc.) may be more inclined to click on other unrelated content, so those searches are more inclined to show results from the user's recommended feed.