This is so simple.
Step 1. Post from your mobile device.
Facebook likes mobile. In fact, they love it. They're all about mobile usage, mobile interaction and most important - for shareholders - mobile revenue. So, their EdgeRank formula is even giving some extra preference to a brand's post made from mobile devices. Posting from your phones can provide up to 39% more interaction. (Another thought could be that most mobile posts contain more images & videos, which help create more engagement.)
Facebook also notes that mobile posts doesn't mean grreater reach.
I would get into the habit of posting to your dealership pages from your phones all the time to take advantage of this opportunity. Plus, there's a better chance you'll capture something that's more engaging, personal and spontaneous when you're posting from your phone. (Besides being more efficient)
Read more about mobile vs. non-mobile post results here.