Lyric discussion by SMUSER17375456 

Cover art for Gasoline lyrics by Dead Weather, The

This song seems to be about a relationship moving too fast. She's afraid of getting in too deep, she would rather keep being afraid of love than surrender to it, so the "cool your engines" line.

"I don't want a sweetheart. I want a machine" is pretty obvious. She doesn't want love, but something simple, automatic, and guaranteed - something that isn't going to fail. Love usually ends in heartbreak, so she'd rather just have a machine.

"To be soft is too easy. Don't get soft on me." It would be easy to fall in love, but don't. Maybe a sexual reference, as well.

Then she says "I love you the most, I do" ... but then "when you're so close to me, I can smell the gasoline", so assuming this is because a machine uses gasoline, she loves him as a machine. She loves what he can do for her (sexually or otherwise), maybe? Rather than how he makes her feel.

I can also take this as, we've already fucked up and fallen in love, but we're not going to fall into the marriage trap - with kids, a house, etc. so let's just slow down and keep things the way they are.