We'll have to put out a "how to search" sticky. It took about 30s to find Stephen's thread. The technique that needed to be used in this case was that you knew what the general title of the thread was "cat 30 valves". If you put those double quotation marks around your search term, then it will look for that specific phrase. If you type it without the quotation marks surrounding the phrase, then it searches for threads containing any of those terms, so it will find threads containing cat, or containing 30, or containing valves. That covers just about every thread on the forum.....
It's not that search is broken; it's that it's different. I can't remember if on the old forum quotation marks were needed to search for the specific phrase. It could have been the case that the default behavior in that search engine was something like "first look for threads that has that specific phrase, then look for threads that have a subset of that phrase (in the same order), then look for threads that have any of the words in that search term" - what seems to be the case with the current search engine is that it appears to search for each individual word in the search term. We'll ask IT if that behavior can be modified.
But in the meantime, if you know the phrase, put it in double quotation marks. If you use "cat" you will indeed get just about every thread because just about every thread has that word in it.

By the way, the actual thread was called "cat thirty valves" using the word, not the number. It appeared second in the result because the search engine also appears to sort the results placing the threads with the most recent use of that phrase first, and older threads later. Go ahead and type that search term in the search bar above including double quotation marks then hit enter. You will get this thread first, then you will get Stephen's thread second.__PRESENT