Hi, i've seen some f150s that put a couple offroad lights behind their grills. does this rob the engine of cool air? and how hard would it be to do...or should you just put them in the opening in the front bumper.

 

I like the lights behind the grill, but they WILL affect the air flow through the radiator. Whether this is significant on your truck in your application is impossible to predict. Keep in mind that when the manufacturers make changes there, they do lots of hot weather testing to prove the design. And nowadays, no parts are over-designed.

Having said that, if you don't alter the seals and baffles, and you're not towing a horse trailer up mountains in summer, you're probably OK. Just keep an eye on your temperature gauge if you do it! If it were me, I'd also have transmission and maybe power steering temperature gauges.

PS: Filling the slots in the bumpers can also affect the air flow as much of the radiator and coolers are down there.