Now that the weather is cooler if people are interested you can try a fun little experiment aimed at reducing underhood temperatures.

Pull the hood seals from the rear of the engine bay - on the cowl. There are two. Drive the truck around a little bit and get it warmed up, then park. Put your hand at the base of the windshield and you will feel the hot air rising out of the engine compartment. That air is being replaced by cooler air from under the truck. That same effect happens any time the truck is moving slow or not at all. At high speeds that is a high pressure zone and the airflow actually reverses and flows down the windshield and through the engine compartment, also cooling it.

Does it help ignition coil, wire loom, and the life of other plastics? Can't hurt. Been running mine like this for years. Of course it totally negates the factory cowl based cabin filter which was always a joke, but no other negative water intrusion effects assuming your cowl is intact. Does let a few more leaves in the cowl plenum that you have to clean out if you park under trees.

Happy Rovering!

 

At higher speeds does the air not flow through the rad and then out the bottom of the engine compartment? I’m not following how the air could go from the windshield down.

 

It does, but there is also a high pressure zone at the base of the windshield at speeds that will force some air down the gap in to the engine compartment. There is also likely low air pressure under the truck behind the front wheels, effectively pulling the air down. If you like experiments tape some yarn tufts taped to the base of the windshield.

 

The yarn tufts are an interesting idea. I work in aviation and yarn tufts are used in flight testing.