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Wish I'd found this thread sooner. Like 2 years sooner.
@chillsworld
I have encountered a couple of the issues highlighted in this thread. My quest began when I traded a 2004 Ford Taurus on a 2007 Dodge Ram 1500. I started with a partial radiator/grill block, and a partial belly panel. I then put fairings in front of the front wheels, and added wheel covers. Later came weather stripping to fill the gap between the hood and the fenders. About then I increased the area of the engine belly panel to 90% or so (had a couple gaps), and extended the belly panel about 6 feet down the length of the truck. Last, I modified the Ford Taurus radiator shroud I was using with my Taurus e-fan, so it stretched across the entire radiator. I thought that’d be even better. Not so, I soon learned.
At this time, i was living in San Antonio, and noticed that coolant temps stayed about 200*F. The T-stat opens at 193, but I didn’t like seeing it sit so high. My electric fan was running more frequently than I thought it should. And, highway mileage wasn’t as good as I thought it should be, given the aerodynamics work I’d completed.
It didn’t help either, that I added a crankshaft under drive pulley (25% reduction, the only one available). It did increase the fun factor though.
At my next oil change, I pulled the belly panels off that were past the engine bay. In this instance, I delayed reinstalling the panels a couple weeks. Oddly enough, that seemed to help highway mpg a bit. Which made me think (to your point, I think) I had sealed the engine bay up such that I was actually preventing or restricting airflow through the radiator. It also occurred to me that mpgs (and temps) were better prior to me stretching the radiator shroud. I also checked my logbook and confirmed this. Nothing enormous, but enough to bother me.
So, I cut out the radiator shroud extensions and put it back to covering only 2/3s of the radiator. I also changed how the second belly panel mounted. Specifically, I left a one-inch height gap between it and the trailing edge of the engine bay panel, with the engine bay panel being the lower of the two. They also overlap about 2 inches in length. Why the change? So I could use the passing airstream to pull hotter engine bay air out of the engine bay, like aircraft engine cowl flaps do. I did the same thing where the second and third panels meet; added a one-inch height gap, with the second panel being the lower of the two.
I also modified (and based on what I read here about pressures on/near the hood, need to do more of) the weather stripping between the hood and fender. I added a couple venting gaps close to the hinged part of the hood. Now, I think I will put these about every 4-6 inches, to help vent the engine bay more. I’m not planning to cut vents in the hood, but if I can tweak a few more things I think I’ll rest easier. Engine temps are better now; hovering at 195-197*F in the summer. And the fan runs less.
One to-do item is adding a small (8-10 inch diameter) fan somewhere between the frame rails, to pull air from the engine bay and out the back. Just need to keep it clear of the driveshaft. This may mean adding a duct in order to get the airflow I am looking for. Or I may need to mount it at the end of the tranny, so I can seal off the passage and vent the engine bay that way…
@gumby79, that is an interesting thought to vent the engine bay out behind the front wheels. In the purple area. Maybe a small fan ducted/mounted behind the front wheels?
Almost forgot. A benefit most may not realize with belly panels. In my truck, they reduce road noise on the highway. And keep the underbelly cleaner. Not to mention reducing fuel burn.
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