My cat used to do this when we would let her out in our garage! she would climb up into the engine of my truck. There was a few times we would go to leave and she would be in there and we would have to pop open the hood and make her get out. so it became a habit to look before we even finished getting ready to leave. it was part of our routine. it's not a way of keeping them out but it's the best way to make sure they are safe! and it might even help you remeber to some routine fluid checks
it's worth a shot!