I've had luck including 3 letter words in phrases and putting the phrase in quotes:
"air filter"
"oil change"
Has any admin tried reducing the minimum to 3 and monitored the results? I run another forum and we had the same problem, including the well deserved complaints! ;) The default was 4 I believe. We set it down to a 3 letter word minimum and have had no problems. This was within the forum search, no Google required. There should be a setting for this without needing Google Search.