I like the looks of the piping for grill block on your truck. I think it would be a lot of trial and error to get the spring rates to work out, that would be the only problem I see. but you could set up a camera to see when they close and open. For me I think that a temperature controlled opening would be easier to fabricate. Or you could still use the piping and and use a vacuum diaphragm that you could salvage off an old furnace. That way under heavy load the block could open? I am mostly just thinking as I am typing
but that is how brainstorming works right?